Sources by Feel — All the Feels

Introduction

People who can’t feel pain tend to die in childhood.Nagasako et al. (2003) write that “the observation that these people [individuals with congenital insensitivity and indifference to pain] often die in childhood because they fail to notice injuries and illnesses has been viewed as compelling evidence that the ability to perceive pain has great survival value” (p. 213). Please note that here in the endnotes, I provide page numbers for quoted material when possible but in some cases I have not. For example, some journals and online sources are not paginated. Apologies for any inconvenience.

It extends to all our sensations, from the urge to breathe to our sense of beauty to awe and even love.See the work on Darwinian aesthetics, such as Dissanayake (2000).

INTRODUCTION “It is not easy to deal scientifically with feelings,” wrote Sigmund Freud,This appears in Sigmund Freud’s Civilization and Its Discontents.

…psychiatry, noted that “trying to test evolutionary hypotheses about emotional states is a devil of a business, one in which it is hard to even pin down exactly what we are trying to explain.”Nesse (2000a) writes this in his review of a book by John Archer. See p. 61.

…emotions are very poorly understood even though there is a long venerable tradition of research pertaining to them, going all the way back to Darwin’s The Expression of the Emotions in Man and Animals.”Ramachandran and Jalal (2017), p. 1. Please note I have rendered the title of Darwin’s book correctly here, instead of quoting the authors exactly because it is clear what they intended.

This issue is called the “hard problem” of consciousness for good reason, so I’ll leave that to wiser heads than my own.Dan Dennett’s Consciousness Explained remains one of my favorites. See also David Chalmers’ The Conscious Mind, Antonio Damasio’s Self Comes to Mind, Mike Gazzaniga’s The Consciousness Instinct, and Stanislas Dehaene’s Consciousness and the Brain for good accounts.

And it’s about time someone organized them.I mean, there have been attempts to organize them. I mention some in later endnotes in this chapter.

Given that it can only do one thing at a time, we need some way to choose among potentially competing—and incompatible—motivations.See p. 116 of Tooby and Cosmides (2008). The model I advance here is very similar to the sketch of emotions in this classic chapter.

This pandemonium of measurements and motivations is, more or less, what we call “consciousness.”This view of consciousness appears, among other places, in Tooby and Cosmides (2008). They write: “In this view, the richly textured representations we experience as feelings constitute our conscious access to a high-bandwidth system of computational devices and program interfaces that amalgamate valuation information with other representations to guide decision-making and to recalibrate decisions…” (pp. 124–125) See also, for example, Panksepp (2005), p. 35: “I assume that the evolution of consciousness was based on the ability of neural tissues to encode biological values.” Values, variables, and measurements are all capturing a similar idea. To my mind, of these, “measurement” is the simplest way to render this.

Throughout the catalog of feels, I’ll propose that we have systems that measure many different aspects of the world that would have been present—and relevant—during our species’ evolutionary history.Tooby and Cosmides (2008) refer to this as a “situation detector.”

Motivating Solutions Often upon measurement—and having the associated feeling—we are motivated to bring about some particular goal because of that feeling.For a similar view, see, for example, Damasio and Carvalho (2013), who write, “Descriptions of feelings tend to reference states of the body. The repertoire of feelings includes thirst, food and air hunger (the urge to breathe), different kinds of pleasure and pain, disgust, fear, sadness and joy, as well as complex social responses such as contempt, shame, compassion and admiration. By contrast, experiences related to exteroceptive senses (vision, hearing, touch, taste and smell) commonly cause emotions…” They distinguish feelings from emotions. I’m lumping them together in the general basket of phenomenological experiences. My account is not too dissimilar from theirs otherwise, though they add the neurophysiological perspective.

Many of these facial expressions are, our anthropologist friends tell us, more or less universal.See Cowen et al. (2021) for excellent recent work on this topic using an intriguing method. They report support for 16 universal expressions, including amusement, anger, awe, contempt, sadness, surprise, and triumph, all of which are addressed here.

Expressions of some—but by no means all—emotions are shared by people around the world.See, for example, Ekman (1992) and Ekman and Friesen (1971) for classic work. More recently, see, for example, Matsumoto and Willingham (2009).

When something negatively related to survival and reproduction happens, the feel is going to be unpleasant.Others have of course made this point. For example, Diener, Kanazawa, et al. (2015) write, “Opportunities (e.g., sexual intercourse) produce pleasure and other positive emotions so that the organism will be motivated to engage in them, whereas threats produce fear and other negative emotions so that the organism will be motivated to avoid them in the future” (p. 235). They cite a 2009 paper by Randolph Nesse and Phoebe Ellsworth for this idea, showing that there is a thread of this concept with some time depth.

…this: To prevent this enterprise from feeling like a reference book, which it definitely is not, I’ll start most feels with a little vignette or observation, many of which are drawn from Greek mythology.I made the decision to work on this book during a lengthy holiday in Greece. While there, I also read Stephen Fry’s books on Greek gods and myths. It seemed to me that the myths illustrated a wonderful array of human feelings and emotions. So the many myths I recount are an homage to Fry, that trip, and, of course, the heroes of yore.

The main reason is that prior approaches, while they might not have been completely devoid of evolutionary theory—I mean, Darwin wrote an entire book about emotionsThe Expression of the Emotions in Man and Animals.

I put some landmarks in this literature in a lengthy endnote.Space constraints prevent me from fully recognizing the extensive and excellent work done by scholars in this area with a thorough review of the literature, which would necessarily take many thousands of extra words. This endnote is therefore a brief acknowledgment of the prior approaches upon which this manuscript builds, though it is necessarily far from encyclopedic. My apologies to those unnamed who have gone before. Here are just a few of the shoulders that the present work tries to stand on.Richard Lazarus’s cognitive appraisal theory argues that emotional responses result from how individuals cognitively evaluate the personal significance of events. According to Lazarus, it is our appraisal of a situation—not the situation itself—that triggers specific emotions, emphasizing cognition as central to emotional experiences. Paul Ekman followed Darwin in focusing on facial expressions to identify basic emotions such as happiness, sadness, anger, fear, disgust, and surprise. Ekman’s work supports the notion that these emotions are biologically innate and recognized across cultures, providing compelling evidence for emotional universality.Robert Plutchik’s psychoevolutionary theory of emotion aligns closely with mine. Plutchik proposed that emotions evolved as adaptive responses. His well-known “wheel of emotions” is a similar attempt at categorization, although Plutchik’s model uses primary emotional categories combined into more complex emotions, without explicitly invoking functional categories as I do here.The “measurement” part of the approach here resonates with ideas developed by Gerald Clore, Norbert Schwarz, and their colleagues, including the “mood as information” model and, subsequently, the “feelings as information” model. Antonio Damasio integrates neuroscience with psychology, emphasizing the critical role of emotions in decision-making and consciousness. His “somatic marker hypothesis” proposes that bodily states associated with emotions guide behavior and reasoning, highlighting emotions as fundamental to rational thought rather than opposed to it.Finally, this manuscript aligns closely with the evolutionary perspectives of Randolph Nesse and even more closely with the views of my former mentors John Tooby and Leda Cosmides. Nesse, while deeply influential, explicitly argues against the strict one-feeling-one-function view I adopt here, whereas my approach directly builds upon Tooby and Cosmides’ foundational evolutionary framework. See Nesse (2004), Figure 2, for a system that starts to get at the sort of system I’m embracing here. His tree structure is not unlike the taxonomic structure I adopt, though he chooses different cuts. Finally, recently Abatista and Cova used a technique called principal component analysis to get at this topic, how to categorize emotions, and came up with three main categories for their concern, the positive emotions. These categories, identified empirically, were hedonic states, social states, and epistemic states. This result is appealing because it roughly recovers the Kingdom structure, though for me, hedonic states has a further cut into Kingdoms 1 and 2. Some relevant citations, which can be found in the reference list, include the following: Abatista and Cova (2023), Damasio (1994), Ekman (1999), Lazarus (1991), Nesse (2019a), Nesse (2019b), Plutchik (1980a), Stein and Nesse (2025), Cosmides and Tooby (2000b).

However, they can be grouped meaningfully by using the central idea of evolutionary analysis: function.See Randy Nesse’s work for a similar way to think about emotions, especially Nesse (1990), Nesse (2005b), Nesse and Ellsworth (2009), and his book Good Reasons for Bad Feelings (Nesse, 2019a).

Feel 1: The Need to Breathe

As carbon dioxide levels increase, the pH of the surrounding fluid declines, which can be detected by chemoreceptors designed for exactly this function.There is some redundancy in this system: Some cells do respond to reduced levels of oxygen in the blood, but this pathway operates only under particular circumstances. The usual pathway is that as CO2 levels increase in the blood, carbonic acid (H₂CO₃) is formed—you’ll see in the formula that you have H2O (water) plus CO2—which then dissociates into hydrogen ions (H⁺) and bicarbonate ions (HCO₃⁻). For this reason, small increases in CO₂ lead to all those hydrogen ions and, in turn, changes in blood pH which—voilà—can be detected. While the primary driver of breathing is CO₂ (via central chemoreceptors in the medulla), peripheral chemoreceptors measure oxygen levels directly and trigger urgent breathing responses during severe hypoxia.

In that situation, your cells continue to produce carbon dioxide while you are also exhaling it, resulting in the level of carbon dioxide in the blood remaining relatively stable.I intend the word relatively to be doing a lot of work here. It obviously won’t stay stable forever, and the rate depends on factors such as the person’s metabolic rate.

Feel 2: Hungry

This view predicted that as we got fatter, we would eat less—a prediction that the obesity epidemic powerfully undermines.Blundell et al. (2015) write that “Fat mass (FM) is weakly, or mildly negatively associated with food intake…”

…not that long ago that prominent scholars in the field remarked quite the opposite, that “little is known, however, as to how the body’s energy needs are sensed, integrated and translated into eating behaviors.”Dulloo et al. (2017), p. 354. Graybeal et al. (2022) write that “the underlying biological mechanisms that explain the role of FFM in tonic/episodic appetite regulation remain unclear” (p. 1).

There is still a lot we don’t understand about hunger.Recently, Beaulieu and Blundell (2021) wrote, “From an evolutionary perspective, there is good reason to propose that the drive to eat should arise from the need to replace the energy used by the body, and should be directed to materials in the environment that supply energy and other nutrients (namely foods). Surprisingly, this concept has been slow to become accepted in biology” (p. 569). I’m not saying that the allergy to evolutionary views inhibited research in appetite and hunger. But it may be worth thinking about why evolutionary ideas are “slow to be accepted” in an area that seems so obviously ripe for functional analysis.

Research has, indeed, demonstrated a reasonably strong relationship between how much energy is used by our fat-free mass and our food—or caloric—intake.Blundell et al. (2012). This relationship is mediated by metabolism. Fat-free mass (e.g., muscle) increases resting metabolic rate, which in turn raises caloric needs and motivates higher food intake.

And much like our rodent relatives, research shows that humans who have their food intake restricted for a significant amount of time respond by bringing more food into the house.See Garretson and Bartness (2014): “Contrary to popular belief, humans exhibit essentially no or little post fast/food restriction-induced increases in eating. Rather, hungry humans ‘overhoard’ by bringing home more food even after mild periods of no food versus their fed counterparts” (p. 2, citations omitted).

…view of the role of ghrelin, finding that in species that go for very long times between meals, such as snakes and chameleons, the genes associated with producing ghrelin are reduced or absent altogether.Pinto et al. (2026).

The hunger system has many components and redundancies.As a team of researchers recently put it, “Given the multiple redundant pathways known to promote satiety, it seems unlikely that a regulatory system would evolve to rely solely on one hormone to promote feeding.” Hopkins et al. (2017, pp. 406–407). So look for more developments on the hunger–hormone front.

For example, when you exercise, your muscles secrete chemicals that start a cascade of reactions, resulting in the upregulation of appetite.Graybeal et al. (2022). I note that this is an active research area, and future evidence might well qualify this pathway.

Feel 3: Full

Recent estimates suggest that as body mass increases, the risks of type 2 diabetes, cardiovascular disease, and kidney disease all increase—in some cases dramatically.Abdelaal et al. (2017).

While damage to this area also results in obesity in humans,Guyenet (2017), pp. 115–117.

These findings hinted at the idea that the body has systems that push one’s motivation to eat so that it returns to a kind of “set point.”Guyenet (2017), pp. 121–124. Note that scholarly debate remains about how to conceptualize a fixed “set point.” See Müller et al. (2010).

Not only that, but they lose fat—not muscle.Guyenet (2017), p. 126.

People born with a leptin deficiency are plagued with constant hunger and often become obsessed with food, nearly to the exclusion of all other interests—a phenomenon also seen, not coincidentally, in cases of starvation.Guyenet (2017), p. 127.

But for those with normal amounts of the hormone, adding more has only small to modest effects.Chrysafi et al. (2020); Mantzoros and Flier (2000).

For this reason, people with more body fat need to eat more to feel the same amount of satiety as someone with less fat.Many messengers play a role in satiety. For instance, a protein called neuropeptide Y causes rats to overeat when injected into their brains. Both insulin and leptin suppress neuropeptide Y, reducing appetite. Subsequent research implicated yet more messengers. Leptin causes increased production of another set of proteins, called melanocortins, which reduce eating in mice. Cone (2005), Schwartz et al. (1996), Stanley and Leibowitz (1985).

Feel 4: Thirsty

According to reports, one of the contestants, a young woman named Jennifer Strange, drank around two gallons of water.CBS News, “Ten Fired After Radio Contest Tragedy,” January 17, 2007. Retrieved from https://www.cbsnews.com/news/ten-fired-after-radio-contest-tragedy/.

For others, it was as much as six liters of water (about 200 ounces).Yamada et al. (2022).

On its website, the Mayo Clinic, vindicating the natural measurement system, summarizes the winner of the debate this way: “drink to thirst.”In some cases, there is an advantage to hydrating past thirst if one is about to have large needs or use a ton of water without nearby supplies, such as at the start of a race in the desert. See, for example, the following page for the advice from the Mayo Clinic: https://newsnetwork.mayoclinic.org/discussion/mayo-clinic-minute-drink-to-thirst/

Feel 5: Gassy (Taking Out the Gas Trash)

There has been increasing interest in this area because recent findings suggest that the microbes in our digestive system play a more important role in health—especially immune function—than previously thought.Belkaid and Hand (2014).

The fact that microbes are critically important might not be all that surprising given how many of these little guys there are: Estimates suggest that each of us hosts tens of trillions of them.Sender et al. (2016).

Only about a quarter of the gas in our gut has to be expelled through the end of the digestive tract.Mego et al. (2017).

In one study, during the first week that a group of healthy subjects was fed a diet with an increased amount of pinto beans, roughly 50% reported increased flatulence.Winham and Hutchins (2011).

These nondigestible bits are fermented by gut microorganisms, producing gas as a byproduct.See Table 3 in Mutuyemungu et al. (2023).

Feel 6: The Need to Poop (Taking Out the Solid Trash)

If material in the intestines is not expelled—leading to constipation—one can experience a number of unpleasant consequences, ranging from discomfort to bleeding to, in rare cases, death.See Heitmann et al. (2021) for this claim and for excellent overall coverage of the topic in this chapter.

One way to study exactly how much pressure people can detect is to insert what is called a barostat balloon into the anal canal of a (well-compensated, one hopes) experimental subject.Thewissen et al. (2000).

Such research allows measurement of exactly how much pressure is needed to give rise to a conscious sensation associated with the need to poop, which turns out to be roughly 8.8 millimeters of mercury.Thewissen et al. (2000).

It’s not a simple matter of releasing the neck of the balloon—muscle contractions add a squish, helping what is inside to get out.Heitmann et al. (2021).

Debate remains about the reason, but one hypothesis is that the practice marks a group’s territory.Dröscher and Kappeler (2014).

This is a stop signal, indicating that some task—here, pooping—has been successfully completed and that other matters can now take priority.Current thinking actually divides the process into four phases: basal, pre-expulsive, expulsive, and—appropriately—end (Heitmann et al. 2021).

Feel 7: The Need to Pee (Taking Out the Liquid Trash)

No source notes for this Feel — the claims in this chapter are basic physiology that needs no citing.

Feel 8: Sleepy (Taking Out Neuronal Trash)

…addition, the state installed slats on one side of the bridge to help withstand high winds, which is why the bridge started “singing” under violent gusts—some say it sounded a bit like a didgeridoo.From the CNN story: https://www.cnn.com/2020/06/06/us/golden-gate-bridge-noises-trnd/index.html

The hunt for the function of sleep was so vexing because, like the Golden Gate Bridge, repairs and maintenance projects occur simultaneously.See, for example, Rechtschaffen (1998), which gives a nice perspective on the state of the art at the time of the publication of that piece. He writes (p. 360), “Given the apparent importance of sleep and its accessibility to scientific study, one would think that its function would long since have been resolved, but this has not been the case. Many theories have been proposed as explanations for limited features of sleep, but to date no theory has explained the diverse data of sleep so parsimoniously as to inspire confidence that the essence of sleep function has been captured.” More recently, Hauglund et al. (2020) wrote, “A broadly accepted theory for the purpose of sleep has yet to be defined” (p. 1).

Pretty much any species with significant amounts of nervous tissue seems to sleep.Bringmann (2018); Lakhiani et al. (2023).

In humans, less sleep has been linked to profound effects on memory and cognition, emotional regulation, and—over the long term—diseases such as Alzheimer’s and cancer.Krause et al. (2017); Ju et al. (2014); Spiegel et al. (1999).

This job is done by the relatively recently discovered glymphatic system,Jessen et al. (2015).

This job is done by the relatively recently discovered glymphatic system, which is responsible for clearing out the waste products your brain producesNote that this is based on early work in mice.

This job is done by the relatively recently discovered glymphatic system, which is responsible for clearing out the waste products your brain produces during wakefulness—waste that could become harmful at high concentrations.Jessen et al. (2015).

At the same time, the system distributes nutrients throughout the brain, including glucose and other critical compounds, helping to keep the brain functioning optimally.This line of thinking is relatively new, and debate continues. A recent review by Chong et al. (2022) concluded, “Overall, the studies reviewed demonstrate a robust relationship between sleep and several CSF indices that represent CSF circulation and approximate glymphatic system exchange” (p. 12).

Getting sufficient sleep improves memory, increases creativity, improves immune function, boosts mood, reduces the risk of injury, and reduces the risk of life-threatening diseases.See Walker (2017) for a thorough account.

This neural timekeeper generates its own rhythmHuman DNA contains a set of genes, including one called CLOCK, that produces proteins over time. As these proteins are produced, they suppress further production of these proteins, making a nifty little negative feedback loop. This loop takes about twenty-four hours to cycle and—voilà—the brain knows, by the buildup of proteins, roughly what time it is. Generally, when the proteins are at their highest concentration you feel the most sleepy; levels go down while you sleep.

This neural timekeeper generates its own rhythm of roughly 24 hours and 11 minutes—close to but not exactly matching Earth’s rotation.Walker (2017) gives a nice account of this work.

Feel 9: Nauseous

The downside of being an omnivore is that you have to figure out what you can eat—and, from time to time, mistakes are made.See Michael Pollan’s The Omnivore’s Dilemma for an excellent treatment.

This is not just an ancient problem: Millions of Americans contract food-borne illnesses every year, in some cases resulting in death.The Centers for Disease Control and Prevention maintains data on this. See https://www.cdc.gov/food-safety/php/data-research/foodborne-illness-burden.

…or toxins have gotten loose in the gut, the body has essentially two ways to respond: hasten their journey through the digestive tract and evict them out the back end or signal the brainToll-like receptors are responsible for measuring the presence of pathogens and starting the cascade of a response, including the production of cytokines. Cytokines activate afferent fibers of the vagus nerve, which sends a signal to the nucleus tractus solitarius in the brainstem, which in turn activates the area postrema, a brain region specialized for detecting circulating toxins. Together, these regions coordinate nausea and vomiting responses to expel potentially harmful substances. See, for example, Dantzer et al. (2008).

…to respond: hasten their journey through the digestive tract and evict them out the back end or signal the brain to send them back the way they came—out through the mouth into the world.Horn (2009).

While the topic has been studied since at least the 1940s, a relatively recent review noted that “no major theory of [motion sickness] can explain all of the key findings.”See p. 130, Previc (2018). See also Dobie (2019), who makes a similar claim.

…the stomach need not be involved at all for one to experience motion sickness: Even if you cut the vagus nerve, the link from the stomach to the brain, you can still feel nauseous.Previc (2018), p. 130.

Many people report a similar experience when they use immersive headsets.Laessoe et al. (2023).

However, when they get feedback that they are in motion—like walking or racing in a car—they often report nausea.See Laessoe et al. (2023).

This conflict, the theory goes, produces nausea.See Previc (2018), p. 131, who says that “sometimes bizarre perceptual outcomes occur during visual-vestibular conflicts that do not lead to MS, such as when a person walks on a rotating turntable while the scene moves with him or her; in this case, the forward-stepping person perceives himself or herself to be walking backward!” [citation omitted; MS is an abbreviation for motion sickness].

In 1977, psychologist Michel Treisman proposed the first adaptationist explanation of motion sickness.Treisman (1977). There is an antecedent decades earlier: Claremont (1931).

After all, in ancestral environments, the reason your senses were out of whack was never that you had been catapulted into space or someone had strapped VR goggles to your head.As Horn (2008) puts it, “It seems unlikely that we evolved this input for nausea and vomiting to keep us away from boats, cars, and airplanes!”

Some cancer drugs, for example, are ototoxic, explaining why certain cancer treatments produce nausea.Lanvers-Kaminsky et al. (2017).

Feel 10: The Urge to Sneeze

Pepper, for example, contains piperine, which binds to these receptors.Jordt and Julius (2002).

The immune system is continuously identifying—again, with a lock-and-key system—foreign entities in the body—such as bacteria, viruses, and dust—and collecting them in batches for disposal.Fahy and Dickey (2010).

While sneezing usually benefits us, a problem with having a lock-and-key system that expels stuff is that it can be exploited by other organisms with fake keys.See Dawkins and Krebs (1979) for the classic account. See also Nesse and Williams (1996).

When an allergy mistakenly identifies, say, a protein in dog saliva as a dangerous invader, it triggers a full immune response—histamine release, inflammation, sneezing, mucus production, the works.Galli and Piliponsky (2008).

This tendency to overreact seems to be more common than in the past.Ng et al. (2023).

One explanation for rising allergy rates in some places is that we have become too good at being clean.Bach (2018).

…might help explain why children raised on farms, who are regularly exposed to animals and diverse microbial environments, tend to have lower rates of asthma and allergies than children raised in highly sanitized settings.Von Mutius and Vercelli (2010).

Feel 11: The Urge to Cough

Had the tree not been removed, Sidorkin might well have died.The Daily Mail reported this story: https://www.dailymail.co.uk/news/article-1169861/Shocked-Russian-surgeons-open-man-thought-tumour--FIR-TREE-inside-lung.html. I cannot, of course, confirm it.

Indeed, among the elderly, coughing disorders—either too much or too little—are a common complaint and even a relatively common cause of death.Sykes and Morice (2021).

Under normal conditions, this pressure difference is relatively modest, about three millimeters of mercury, give or take.Pleil et al. (2021).

Estimates of the maximum pressure of an exhale are roughly between 44 and 99 millimeters of mercury.Lausted et al. (2006).

The maximum pressure of a cough, in turn, has been estimated to range between an impressive 80 and 125 millimeters of mercury.Martin and Loth (2009).

And in the doctor’s office, we can voluntarily produce a close facsimile of a cough, though recent evidence suggests that there are subtle differences between these voluntary coughs and more naturally occurring ones.Magni et al. (2011). They conclude, “The neural mechanisms subserving muscle recruitment and, in consequence, the motor pattern and mechanical characteristics of the two cough modalities not only differ considerably but also are differentially affected in disease.”

These characteristics make coughing seem more like a voluntary behavior as opposed to a purely involuntary one—or a “reflex,” as it is often called.For example, see Widdicombe (1995). More recently, consider Sykes and Morice (2021).

Feel 12: Dizzy

In 2015, one estimate put the medical cost of falls at around $50 billion, a figure that has no doubt only increased over the last decade.The Medical Costs of Fatal Falls and Fall Injuries Among Older Adults. PMC (nih.gov).

Recent data from the Centers for Disease Control and Prevention indicate that “falls are the leading cause of fatal and nonfatal injuries among older adults.”Older Adult Falls Data | Older Adult Fall Prevention | CDC. Available here: https://www.cdc.gov/falls/data-research/index.html. See Centers for Disease Control and Prevention, National Center for Injury Prevention and Control. Web–based Injury Statistics Query and Reporting System (WISQARS).

This condition, called benign paroxysmal positional vertigo, causes dizzinessDizziness has traditionally been divided into four types. Vertigo is the perception of motion, presyncope is the sense one is about to faint, disequilibrium is like a loss of balance, and light-headedness is, well, just what it sounds like. For this chapter, I decided to keep things simple by avoiding this set of distinctions, which some have argued might not be useful, at least from a medical perspective (Muncie et al., 2017, p. 154).

Before your body can compensate for this drop in pressure, less blood reaches your head and brain, including the inner ear and, critically,Karatas (2008) indicates that “vertigo…can be of peripheral or central origin” (p. 357).

Feel 13: Fatigued

FatigueAs I looked at the research on the topics for this section of the book, I was continually surprised by, on the one hand, what was known and, on the other, gaps in the research. Here, as in other areas, there are important gaps, at least as of ten years ago or so: “Despite flourishing interest in the topic of fatigue—as indicated by the many presentations on fatigue at the 2015 Annual Meeting of the American College of Sports Medicine—surprisingly little is known about its effect on human performance.” Enoka and Duchateau (2016).

Fatigue has been defined as “the subjective experience of weariness or exhaustion that occurs in the context of a specific motor or cognitive task,” often—but not always—accompanied by a decrease in performance.Behrens et al. (2023).

As your muscles work, they consume oxygen and build up metabolic byproductsThese include inorganic phosphate, hydrogen ions, and lactate (lactic acid), which increases acidity. See Behrens et al. (2023), p. 11.

As your muscles work, they consume oxygen and build up metabolic byproducts that can eventually pose a risk.A small technical note on lactate. Historically, lactate was cast as something of a villain of fatigue, a metabolic waste product responsible for muscle burn and performance decline. More recent research has upended this view. Lactate is now understood as a key energy currency, shuttled between tissues and even used by the heart and brain as fuel. During exercise, your body uses it, sometimes preferentially. Rather than signaling exhaustion, rising lactate levels might indicate that your body is reallocating resources to keep going. Brooks (2009); Gladden (2004).

As fuel decreases and waste builds up, muscles lose their capacity, and your discomfort increases.Mauger (2013).

These and other changes put constraints on the maximum performance of a given set of muscles.See Behrens et al. (2023), Section 3.1, pp. 9–10 for details.

And as your body heats up from the work of your muscles, the risk of overheating—and in extreme cases, heat stroke—goes up.Tucker (2009), p. 393.

That’s why exercising feels bad and not good: The sensation of fatigue is a stop-unless-necessary feeling.Tucker (2009) puts it this way (p. 393): “If exercise was ultimately limited by the depletion of energy substrates, with no anticipatory component, then it would be expected that the RPE [rating of perceived exertion] would increase rapidly only at the end of exercise when the muscle glycogen stores were approaching critically low levels.”

It’s probably a bit of both.To take one example, see Jay and Kenny (2009). Noakes (2012) presents a classic account of the risk view in his “central governor” approach.

This measurement is complex, and how much fatigue you experienceBorg (1982).

…measurement is complex, and how much fatigue you experience depends on a whole array of factors: how much force is being exerted by muscles, your heart rate, your breathing rate, and your body temperature.Tucker (2009), p. 393.

The feeling of fatigue also seems to take into account your fuel reserves,Noakes (2004).

The feeling of fatigue also seems to take into account your fuel reserves, the amount of oxygen being extracted from the blood, and lactate concentration.Tucker (2009).

Reports of fatigue seem to integrate all of these different psychological and physiological sub-measurements.Tucker (2009), p. 392.

Research has shown, for example, that giving cyclists painkillers can increase their power output.Mauger et al. (2010).

In 2019, CNN reported that Zac, a 16-year-old boy, lifted a Volkswagen Passat to rescue a neighbor trapped underneath.Available at https://edition.cnn.com/2019/09/26/us/teen-saves-neighbor-car-trnd.

Feel 14: Pain

But if you cannot measure pain or aren’t motivated to do something about it, small and great dangers pose damage to the body.Nesse and Schulkin (2019).

Two scholars sum it up this way: “Pain always seems like a problem, but usually, it is part of the solution.”Nesse and Schulkin (2019).

Unfortunately, there are many ways to damage tissue.Kolodny et al. (2021).

These act as distress calls, letting allies know we may need help.Nesse and Schulkin (2019) write (p. 215), “In addition to protecting against tissue damage, pain also promotes healing by limiting movement and disruption. Pain can also communicate danger and the need for help.”

…end with Schopenhauer, who opined on the human purpose: “If the immediate and direct purpose of our life is not suffering, then our existence is the most ill-adapted to its purpose in the world.”Arthur Schopenhauer, On the Suffering of the World.

This Kingdom of External Dangers and Opportunities embodies what Hamlet put best: “There is nothing either good or bad, but thinking makes it so.”Hamlet, Act II Scene 2.

A fitness-bad stimulus, by contrast, posed a threat or detracted from fitness.Barrett (2015).

What was fitness-good about dancing?”Bloom (2010), p. 57. James (1887) made a similar observation.

Feel 15: Disgusted

The short version is that many people won’t.Rozin et al. (1986).

They represent a tremendously important adaptive problem, posing a threat in every ecology in which our ancestors evolved.Fumagalli et al. (2011).

Humans are, not by coincidence, incredibly sensitive to the presence of these compounds, as we saw in the chapter on feeling like one needs to expel gas.Wicker et al. (2003).

Similarly, bodily fluids outside the body evoke disgust, for the same reason, that they pose a risk of contagion or toxicity.Tybur et al. (2013).

The sour taste bud might be designed to measure acids, which can indicate the presence of certain kinds of bacteria.DeSimone et al. (2001).

Together, the information from the various senses measures the potential cost of contact with the various objects of disgust.Tybur et al. (2013) refer to the “expected value of contact.”

We try to distance ourselves from things that give off these cues, as well as the people who give off these cues,Kurzban and Leary (2001).

The second Class of disgust is to do with sex.Some scholars would add a third Class, moral disgust, as in, stealing candy from babies is a disgusting thing to do. My view (see, e.g., Royzman and Kurzban, 2011) is that people aren’t genuinely feeling disgust when it comes to these moral violations, but are recruiting the language of disgust to express their moral condemnation starkly.

Most basically, many people feel disgust at the thought of having sex with individuals who are not of the necessary age, sex, and species for reproduction.This is a fraught issue. Some people are not disgusted by the idea of sex with people who fit this description. And, of course, the link between disgust and homosexuality should be understood as a pure empirical claim (e.g., Terrizzi et al., 2010), nothing to do with the normative question.

Having said that, the thought of having sex with those who are not of the required age, sex, and species can evoke disgust.Tybur et al. (2013).

Certainly most (healthy) individuals find the idea of sex with a member of a different species and someone who has not yet reached reproductive age to be quite disgusting.Of course there are exceptions, but the modern conception of such preferences is that they constitute pathologies. Beetz (2008), for example, writes that for some groups, though not necessarily for all peoples historically, “all sexual human-animal interactions are judged as severe animal abuse, probably due to the related emotions of disgust and abhorrence” (p. 217).

This “kin detector” uses a number of different cues.Lieberman et al. (2007).

But the measurement of the disgust system, prolonged co-residence, led to the associated motivation, an aversion to having that kind of relationship.See Lieberman and Patrick (2022) for an extended treatment.

Feel 16: Itchy

…in their saliva that makes our skin more permeable, secretions that dilate our blood vessels and reduce our inflammatory response, and, if that weren’t enough, in the mix are also anticoagulants, slowing down clotting.Phillips et al. (2020).

Leech secretions also have analgesic (pain-reducing) effects, meaning that people like me will feel no pain as the little devils drain my life force.Sig et al. (2017).

Some estimates indicate that globally, one in three people experiences itchiness in any given week.Najafi et al. (2021).

Acute or chronic itch affects perhaps 15% of the population and can be very unpleasant.Cevikbas and Lerner (2020).

One recent review noted that itch can lead people to contemplate suicide.Najafi et al. (2021), p. 1058.

Back in the 17th century, the German physician Samuel Hafenreffer defined itchingHe referred to it as “pruritus.”

Back in the 17th century, the German physician Samuel Hafenreffer defined itching as “an unpleasant cutaneous sensation which provokes the desire to scratch,” a definition that remains in wide use today.Rinaldi (2019).

The current prevailing view about scratching is that we do it “to remove environmental insults from the skin, especially arthropods.”Cevikbas and Lerner (2020).

And itching isn’t just a kind of pain.See Ikoma et al. (2006). They conclude, “Itch and pain are different sensations that are processed by distinct sets of neurons” (p. 544).

The itch/scratch apparatus is specialized and complicated.Itch neurons might have a role to play as well in the pain system. But it doesn’t look like nociceptors play a role in itch. See Cevikbas and Lerner (2020).

In fact, many readers are likely to have felt a little itch while reading this chapter: Just learning about itchiness can cause it.Holle et al. (2012).

Feel 17: Tickled

Now, while Darwin himself opined on tickling,Darwin (1872). Darwin observed that the human response to humor and to tickling were similar. As with so many other feels, research is sparse. Harris and Christenfeld (1997) wrote, “Empirical work on the relationship of tickle and humor is almost nonexistent” (p. 104). There has not been much research on the topic since then, though Alan Fridlund and Robert Provine represent important exceptions, and there has been significant work on the neuroscience of itch.

For that reason, I have taken some liberties and presented my own thoughts about what ticklishness is measuring and motivating, with somewhat fewer supporting citations than usual.Portions of this essay appeared on the Living Fossils under the title “Ticklishness.”

…are a bit hard to pin down, but, roughly, tickling is touching sensitive parts of another’s body, eliciting, under at least some conditions, helpless laughter by the person being tickled, a phenomenon called gargalesis.Leavens (2009). See Demuru et al. (2025) for a discussion of this phenomenon in our close relatives, bonobos. Scholars distinguish between gargalesis and knismesis, which is the sort of tickle associated with light touch, not always eliciting laughter. My focus here is on gargalesis. See Varlamov and Skorokhodov (2022).

Intriguingly, another reliable result of being tickled is trying to move away from the tickler and protecting ticklish areas of the body.Demuru et al. (2025) review some of the tickling literature. See also citations therein.

Tickling seems to have two different modes, one good and one bad.As one recent review by Demuru et al. (2025) put it, tickling “elicits agent-dependent responses (pleasant/unpleasant depending on social bond)” (p. 1). Indeed, they suggest that the “unpleasant sensation might support the development of combat skills through the promotion of play-fighting,” (p. 2) citing Harris (2012).

Here are some broad findings about tickling: It’s difficult, if not impossible, to tickle oneself.See Proelss et al. (2022). The New York Times ran a story (“Anatomy of a Tickle is Serious Business at the Research Lab,” by Carol Kaesuk Yoon, June 3, 1997) about this. Note that there is evidence that people with the traits typical of schizophrenia can, indeed, tickle themselves (Lemaitre et al., 2016).

Tickling declines with age.Provine (2004) wrote that “the frequency of tickle frolics declines precipitously (about 10-fold!) after the age of 40…” (p. 217). See also Leavens and Bard (2016). This trend holds for our non-human relatives as well, as discussed by Demuru et al. (2025).

It’s rare between strangers.Provine (2004) wrote that “people tickle and are tickled overwhelmingly by friends, family, and lovers…” (p. 217).

The areas that are ticklish include sensitive areas, such as the neck, armpits, and waist.Proelss et al. (2022).

Feeling tickled, perhaps, measures forbearance: How much am I not being hurt by someone who could, in principle, hurt me?Provine (2004) proposed that the function of the response to being ticked might be communicative. Demuru et al. (2025) entertain the idea that the function is more to do with behavior than communication, the idea that “tickling has evolved to develop combat skills” (p. 9).

In contrast, as Darwin noted, “A young child, if tickled by a strange man, would scream from fear.”This appears in The Expression of the Emotions in Man and Animals (Darwin, 1872).

Organisms can benefit from signaling submission.Selden (2004) makes a similar suggestion, noting that “in tickle play there are elements of dominance and submission…” I was unaware of this article when I wrote the essay that appears on Living Fossils. I regret the omission.

This is valuable to both the subordinate and the dominant because once submission has been signaled, there is no need for further violence, which would be costly for both.Alexander makes a similar suggestion at the end of the piece in The New York Times, cited above. See also Selden (2004).

…of all of our ape relatives, including chimps, gorillas, and orangutans, respond similarly to the way humans do to being tickled, making laugh-like sounds and, in some cases, moving to protect the sensitive area.Ross et al. (2009).

Additional research suggests that the response to being tickled is found in even more distantly related species, including rats.Leavens and Bard (2016).

To tease these apart, let’s divide tickling into its benign and more sinister varieties.Note again the distinction alluded to previously between gargalesis and knismesis. See Varlamov and Skorokhodov (2022) for a recent review.

Our ape relatives show the same pattern.Demuru et al. (2025).

This aspect of tickling might explain why there is a sex difference in laughing in response to ticklingSvebak (2021) wrote that “females appeared more often than males to respond overtly with laughter” (p. 687).

There’s the time that Hannibal Lecter kissed Clarice in Hannibal.He kisses her in the book but doesn’t quite make contact in the film version.

Courtship is complicated, rife with ambiguous signals.Gersick and Kurzban (2014).

Uncontrollable laughter makes one vulnerable in the same way that baring one’s neck does.See Provine (2004).

Feel 18: Over-Stimulated

As tensions rose, the government deployed surveillance measures, including cameras equipped with facial recognition technology to monitor and identify participants.For a general account of these protests, see the Wikipedia page: https://en.wikipedia.org/wiki/2019%E2%80%932020_Hong_Kong_protests

The lasers obscured the protesters’ identities by creating a blinding burst of light on camera feeds, in many cases inflicting permanent damage on the camera sensors.An account of this is offered here: https://petapixel.com/2019/08/26/hong-kong-protester-lasers-are-frying-photographers-cameras/. From the article “Protesters in Hong Kong are widely using handheld laser pointers in their anti-government demonstrations, and some photographers on the ground are reporting damaged sensors after their cameras were exposed to the powerful beams of light.”

However, when exposed to intense, concentrated light, such as a laser, they can become overloaded and damaged, leaving “blind spots” or completely disabling the device.This has been known for some time. See https://ymcinema.com/2021/08/04/sony-says-do-not-directly-expose-the-lens-to-laser-beams/

Rods, for example, can detect a single photon of light.Tinsley et al. (2016) write, “Rod cells respond to individual photons, yet whether a single-photon incident on the eye can be perceived by a human subject has remained a fundamental open question. Here we report that humans can detect a single-photon incident on the cornea with a probability significantly above chance” (p. 1).

The features that produce this sensitivity, just as in the case of cameras, make these sensors vulnerable to damage.Hunter et al. (2012) write that “rods and cones, which require photopigments to absorb photons as the first step in seeing, are much more likely to be damaged by excess amounts of visible light” (p. 29).

…photoreceptor/RPE [retinal pigment epithelium] complex must maintain a delicate balance between maximizing the absorption of photons for vision and retinal image quality while simultaneously minimizing the risk of photodamage when exposed to bright light.”Hunter et al. (2012), p. 28.

Less intense light, extended over time, can cause similar damage or even cell death as a result of chemical changes produced by intense light.Hunter et al. (2012) write, “Brief exposure to extremely bright lights can produce an immediate thermal injury. On the other hand, exposure to light for an extended period of time may result in chemical changes in retinal cells that ultimately result in cell death. The latter is known as photochemical damage” (p. 2). They also write that “sequential transfer of energy from a photon to a photosensitive molecule, and then to oxygen causes changes in electron orbitals, creating reactive forms of oxygen, such as singlet oxygen (1O2). The subsequent reaction of singlet oxygen with surrounding molecules can break their molecular bonds, a process called photoxidation. If too many of these events occur, they can eventually result in cell damage or death” (p. 3). I felt that the details of the damage were below the threshold to include in the main text, but this provides a sense of why light can damage cells. The energy in the photons is changing the nuclear chemistry.

The typical human ear can detect frequencies from about 20 Hertz to 20,000 Hertz,Møller and Pedersen (2004).

In terms of amplitude, the ear can handle sounds from 0 decibels to sounds as loud as 120–140 decibels,Møller and Pedersen (2004).

The hair cells in the cochlea are similarly delicate, but even worse, they can’t regenerate if damaged.Smalt et al. (2020), p. 94: “In humans, damaged and lost hair cells cannot regenerate, so the resulting hearing impairment is permanent.”

Over time, this results in reduced sensitivity to certain frequencies or overall hearing loss.Smalt et al. (2020), p. 95: “Dramatic cochlear synaptopathy (loss of synaptic connections) can occur after exposure to continuous noise.”

This reflex acts like a built-in volume dampener but has limitations—it cannot protect against sudden, explosive sounds due to its slight activation delay.Mukerji et al. (2010), p. 170: “In man, the stapedius contracts in response to intense low frequency acoustic stimuli…increasing middle ear impedance and attenuating the intensity of sound energy reaching the inner ear (cochlea).”

So we also have appropriate motivation, including the startle response.Koch (1999): “Startle is a fast response to sudden, intense stimuli and probably protects the organism from injury by a predator or by a blow.”

Feel 19: Too Hot and Too Cold

In the huddle, temperatures can rise to 37.5°C, which is too hot for the birds, which explains why penguins sometimes peel off the huddle.Ancel et al. (2015). For the initial measurements, see Gilbert et al. (2006).

Feel 20: Afraid

When the Enterprise—the starship or the aircraft carrier—detectsThe USS Enterprise (CVN-65) was decommissioned in 2017. So I suppose technically I should be using the past tense here.

These situations all present threats, though the exact nature of the danger differs.Marks and Nesse (1994).

Often, but not always, the best next move is going to be to escape, fight, or freeze.Marks and Nesse (1994) add submission to this list. I consider the social world in its own Kingdom, so I omit that option here.

Other species show a similar pattern.Gibson and Walk (1960).

Many fears, from the fear of loud noises to spiders,Rakison and Derringer (2008).

Experimenters subsequently made a loud noise when they presented the rat to Albert, and eventually, he came to fear the rat and rat-like stimuli.Watson and Rayner (1920).

Learners seeing the fear reaction to a snake did subsequently show fear of snakes, but those seeing a monkey afraid of a flower showed no such fear of flowers.The snake-versus-flower result described here is from Cook and Mineka (1990); the original observational fear-conditioning study, using live models, is Mineka et al. (1984). See also Öhman and Mineka (2003).

Humans show similar effects.Olsson et al. (2020).

The ability to distinguish dangerous objects comes in early: Infants of only five months look longer at spiders than at control stimuli.Rakison and Derringer (2008).

In short, while some kinds of fears develop without special help—heights and spiders—humans, like monkeys, acquire fears both from individual experience and by observing what others fear.Olsson et al. (2020).

As one review recently put it, “Examples of innate fear include fears that are triggered by predators, pain, heights, rapidly approaching objects, and ancestral threats such as snakes and spiders.”Ren and Tao (2020), p. 1.

An object heads toward us in our peripheral vision, and we duck without having to think about it.See Pessoa and Adolphs (2010). I hedge here because there is, as ever, scholarly debate about this topic. The claim has been that fear processing and reaction occurs subcortically—that is, in structures below the level of the cortex—which is why reactions can be so fast.

With all the different possible threats, the higher processing areas of the brain are required to sort out what the threat is, how big it is, and what the proper countermeasures are.Ren and Tao (2020).

This asymmetry of costs explains why we seem to be designed to over- rather than under-react.For a brief account, see Nesse (2019a).

Feel 21: Anxious

Anxiety is designed to prepare for what is to come.This approach is similar to that taken in the Diagnostic and Statistical Manual, where anxiety is understood to be about anticipation of what is to come.

Some estimates suggest that nearly a third of people worldwide during the course of their lives will have a diagnosable anxiety disorder.Nesse (2019a), p. 68.

This problem might well be getting worse, leading Jon Haidt to propose that today’s young people are The Anxious Generation.According to NIMH, about 19% of U.S. adults have an anxiety disorder in a given year, and about one-third experience an anxiety disorder at some point in life; rates for some age groups are similarly high. See The Anxious Generation by Jon Haidt for an excellent recent treatment. For relevant data, see https://www.nimh.nih.gov/health/statistics/any-anxiety-disorder.

This distinctive human ability carries many benefitsGilbert and Wilson (2007).

This distinctive human ability carries many benefits and, some have argued, might explain why humans have been so successful at filling the planet’s varied ecologies.Vale et al. (2022).

Anxiety is one feeling that motivates this planning.Miloyan et al. (2016) summarize this view, stating that “anxiety enables individuals to take more advanced precautionary measures” and “the ultimate function of anxiety is to predict potential threats to fitness so that action can be taken to prevent these threats from eventuating” (p. 5).

As Randy Nesse has emphasized,Marks and Nesse (1994); Nesse (2005a).

Patients with this disorder report that the bulk of their time is spent worrying.Nesse (2019a), p. 81.

This sort of counterfactual thinking can prepare you for the next, similar situation.Roese (1997).

Because humans can simulate what might have been, we can learn by considering how different reactions might have led down different paths.Byrne (2016).

Indeed, there is some evidence that people who are more anxious overall run these mental simulations more oftenParikh et al. (2020). See discussion on p. 1742.

There is a positive relationship between more counterfactual thinking and, for example, post-traumatic stress disorder.Gilbar et al. (2010).

There seems to be a Goldilocks amount of counterfactual thinking.See Parikh et al. (2020).

Nesse reports that many of his patients in the clinic experience paralysis as their anxiety rises.Nesse (2019a), p. 73.

Feel 22: Panic

At the Battle of Marathon, the Persians, led by the generals Datis and Artaphernes, under Darius I, heavily outnumbered the defending Greeks by roughly 25,000 against 10,000.Sources are, of course, scarce. The numbers and values I use here seem to be roughly the consensus among historians, though there is, as always, disagreement.

According to some accounts, it was Pan who led to the rout at Marathon.Sekiya (2016).

When panic entered into the Diagnostic and Statistical Manual of the American Psychiatric Association, it was defined as “the sudden onset of intense apprehension, fear or terror often associated with feelings of impending doom.”Barlow et al. (1985).

When one panics, there is some combination of a shortness of breath, elevated heart rate and blood pressure, chest pain, dizziness, hot or cold flashes, sweating, shaking, and a powerful sense of fear.See Barlow et al. (1985) for early work on symptoms of panic attacks.

Panic attacks are associated with strong activation of the autonomic nervous system, parts not subject to conscious experience or control.Hamm et al. (2014). See Section 5.0.

It’s a feel telling you, rightly or wrongly, that you are on the precipice of disaster.In the animal literature, fear reactions have been discussed under the rubric of the “threat imminence model.” See, for example, Fanselow (1994).

It is probably not a coincidence that patients diagnosed with panic disorder “exhibit exaggerated safety behavior.”Hamm et al. (2014).

(I once saw a video of a bunch of fish left in a net on a dock.https://x.com/TheFigen_/status/1853456611328561436

Research confirms that such attacks are “often associated with an overwhelming surge in behavior with robust flight reactions.”Hamm et al. (2014). See Section 2.3.

I think there’s a reason that the WWII-era poster telling people to “keep calm and carry on” is perceived as a good slogan for England in World War II.About 2.5 million posters were printed in 1939 but were never actually displayed. They became famous only after their rediscovery around 2000.

Feel 23: Sensory Pleasures

Grooming clearly plays a social role: Physically larger species don’t groom more, but species that live in larger social groups do.Dunbar (2010).

…their arms through holes in the enclosure so visitors can stroke them—and from neuroscientific studies we know that there are specialized nerves—called C-tactile afferents—that, it is believed, give rise to a feeling of comfort.Jablonski (2021), p. 118: “The type of slow, gentle stimulation of hairy skin that activates CT afferents occurs during social interactions between primates, most especially during grooming, cuddling, and huddling.” And then later Jablonski writes (citation omitted), “This sensation is interpreted by the limbic-related cortex and represents an innate, non-learned response that can be described as a feeling of diffuse comfort.”

Grooming is a way to signal not only trustworthinessDunbar (2010) p. 266

It’s no wonder grooming reduces heart rate and blood pressure.Jablonski (2021).

Touch evokes feelings of pleasure in humans, reducing negative emotions and conveying support and sympathy.For a review, see Ellingsen et al. (2016). They note that context matters. As in the case of tickling, a gentle caress by an enemy is not, of course, comforting or pleasant. As these scholars note, there are a number of similar top-down effects.

Our preferences for those foods persist, not rigidly, but markedly, over the course of our lives.See Michael Pollan’s The Omnivore’s Dilemma for an excellent and very readable treatment of this and many other food-related issues.

In his book How Pleasure Works, Paul Bloom, on this topic, stated it baldly, “Nobody can yet explain most of the variation in food preferences.”Bloom (2010), p. 29. Marvin Harris’ (1998) Good to Eat isn’t recent but still an excellent read on this topic.

When two artists tried to determine what the most preferred painting was around the world, they discovered that it was a landscape that included water and animals.See Dutton (2009), p. 14.

…might well have been a fairly good place to make home, with fresh running water, resources to support plants, and animals to gather and hunt, respectively, and perhaps spots affording both prospect and refuge.See Dosen and Ostwald (2016) for a discussion of evidence, which they characterize as “inconsistent.”

At the top of the list, for better or worse, is the pornography industry, which reveals that people will pay to see images, especially moving ones, of attractive people.Salmon (2012).

Babies have been shown to have a preference for looking at attractive faces at an age well before socialization might have shaped those preferences.Slater et al. (1998).

Humans are not alone in this: Male rhesus macaques will pay—in the currency of foregone sips of juice—to see the hindquarters of females of their species.Deaner et al. (2005).

When scholars such as Elizabeth Spelke wanted to investigate what young babies already knew about the world, they used what is called a habituation paradigm.Spelke (1990).

Darwin himself felt that one of the toughest mysteries was why people liked music and singing.See Bloom (2010), p. 122.

Generally, while there is tremendous cross-cultural variation,McDermott et al. (2016).

The usual explanation for this pattern is that the combinations of notes that we like have certain mathematical properties, such as the ratio of the frequencies of the notes in a perfect fifth, 3:2.Cousineau et al. (2012).

Feel 24: Aesthetic Pleasures

If one supposed that the average American sleeps eight hours per night (they do not),It’s closer to seven, according to https://startsleeping.org/statistics/, retrieved on 11/25/2024.

If one supposed that the average American sleeps eight hours per night (they do not), commutes about one hour round trip (they do),This value is from the U.S. Census Bureau, Census Bureau Releases New Brief About Travel to Work Since Pandemic’s Onset, published 2/2/2024, and retrieved on 11/25/2024: https://www.census.gov/newsroom/press-releases/2024/travel-to-work-since-pandemic.html.

If one supposed that the average American sleeps eight hours per night (they do not), commutes about one hour round trip (they do), and works nine hours with one hour for lunch (almost),It’s also not that far off. According to Bureau of Labor Statistics data, people who work full time put in above eight hours of work. Retrieved on 11/25/2024 from https://www.bls.gov/charts/american-time-use/emp-by-ftpt-job-edu-h.htm.

Recent data suggest that Americans spend five hours per day, on average, watching TV, including streaming,This value is from Neilsen, Connectivity is driving how Americans are engaging with TV, published March of 2023, retrieved 11/25/2024 from https://www.nielsen.com/insights/2023/connectivity-is-driving-how-americans-are-engaging-with-tv/.

Recent data suggest that Americans spend five hours per day, on average, watching TV, including streaming, or 35 hours per week—more than half of all that time.Estimates vary. See, for example, Gottschall (2012) and Dissanayake (2001).

This chapter humbly explains what the pleasure one gets from art is measuring and motivating.For excellent treatments, see, among others, Jonathan Gottschall’s The Storytelling Animal, Denis Dutton’s The Art Instinct and Lisa Zunshine’s book Why We Read Fiction and her article in the Skeptical Inquirer. I note that Joseph Carroll, another luminary in the area, as recently as 2018, wrote, “Evolutionary theorists have reached no consensus on the adaptive function of the arts…”

Because this is a book about feels, I touch only lightly on the question of why people produce art, focusing instead on why people consume it.In my view, the best account of why people produce art remains Geoffrey Miller’s The Mating Mind.

…art are the same as the ones that light up when we look at, in their words, “objects of evolutionary importance, such as the desirability of food items or the attractiveness of potential mates.”Brown et al. (2011).

Along similar lines, we find it rewarding to observe wrongdoers getting punished.It has been known for some time based on research in neuroscience that observing punishment is rewarding. See, for example, Singer et al. (2006) and De Quervain et al. (2004).

It’s difficult to test this idea because it’s not clear exactly how to quantify matters, but my survey of country musicKurzban (2012).

Philosopher Denis Dutton, for example, presents an argument that “providing cultural grounding and even technical knowledge was a major purpose of the Iliad and the Odyssey,”Dutton (2009), p. 115. Dutton presents the argument of Eric Havelock on this topic. See also Gottschall (2008, 2012).

…we humans are an information-intensive species, needing information about any number of aspects of life, ranging from what the local moral norms are to where game can be found to which plants are safe.Sugiyama (2001) was an early exponent of this view.

Stories are particularly good at this function because narratives can provide rich descriptions of contexts and situations and, in addition, people are good at remembering information in narrative form.See Sperber (1985) and his later work on this topic.

Paul Bloom pointed out that watching police dramas might well teach viewers about their Miranda rights, which he dubs “a painless way of learning about reality.”Bloom (2010), p. 167.

In sum, stories provide frameworks to pose hypotheticals and think through them, giving our cognitive apparatus a workoutZunshine (2006b) asks, “How is reading a detective novel similar to lifting weights at the gym?”

Geoffrey Miller has argued that artistic creation is fundamentally display—a complex cognitive performance that signals mental fitness to potential mates.Miller (2001).

Famous virtuoso musicians are generally ignored in subway tunnels, suggesting that fans of the musician enjoy being at the concert more than they enjoy listening to the music.Bloom (2010), p. 118.

Feel 25: Piquancy (a.k.a. Spiciness)

Capsaicin, a molecule found in a number of plants, including especially chili peppers, doesn’t interact with taste buds—it hijacks the specialized receptors whose job is to detect dangerous heat (above 43°C).Specifically TRPV1 receptors. Caterina et al. (1997).

Peppers can range from zero on this scale—for example, bell peppers—all the way to the millions, though peppers that spicy are dangerous to consume.See Doligalska et al. (2025) for a recent review.

Psychologist and food expert Paul Rozin referred to eating spicy foods as “benign masochism.”Rozin et al. (2013).

As with many of the sensations, there is the usual amount of scholarly debate about the answer to this question.In this chapter, I take a position floated initially by Sherman and Billing (1999). Bromham et al. (2021) dissent. Hagen et al. (2023, p. 599), in turn, suggest the dissenters “went too far” with their concerns. And so it goes.

First, some cultures use more spices than others,Sherman and Billing (1999).

First, some cultures use more spices than others, and how much people like spicy food varies a lot due to differences in genes, personality, experience as a child, and so on.Spence (2018).

Still, people in all cultures add at least some spices to their foods when they can.Hagen et al. (2023).

In one siege of ancient Rome, the besieger demanded pepper as part of the ransom.Nilius and Appendino (2013). As usual, there is some scholarly dissent regarding these claims, so take them with a pinch of cinnamon.

Piquancy, arguably, had a revolutionary effect on world history: Columbus went West, in part, to try to find a faster trade route to obtain pepper and other spices.Standage (2009).

Today, about a quarter of the people on Earth eat chilies every day.Spence (2018).

Pepper, for example, not to mention tea, has antimicrobial effects for a surprisingly wide array of pathogens,Hagen et al. (2023).

Pepper, for example, not to mention tea, has antimicrobial effects for a surprisingly wide array of pathogens, including one particular species of fungus.Tewksbury et al. (2008).

Some scholars have recently argued that as our ancestors increasingly consumed meat over the course of evolution, the benefit of getting the antimicrobial effects of consuming substances that fought them, such as peppers, increased.Hagen et al. (2023), p. 598.

It’s worth noting, for comparison, that many of our non-human animal cousins don’t seem to like spicy food,Carstens et al. (2002) report that animals prefer food without pepper to food with pepper, when the choice has been studied systematically.

It’s worth noting, for comparison, that many of our non-human animal cousins don’t seem to like spicy food, though rats and chimps can learn to like it.Spence (2018).

Spices, particularly those with strong antimicrobial properties, could have helped prevent disease and decrease the speed at which meat spoiled.Again, bear in mind that Bromham et al. (2021) contest this account. They find strong relationships between spice use and indicators such as poverty and lower GDP. These relationships might in turn lead to the relationships found by Sherman and Billing (1999).

In addition, consuming spices might have positive effects on health, from improving cardiovascular function to suppressing cancer.See Nilius and Appendino (2013) for an excellent brief account of spices in history.

The preference for spiciness has a cliff, and our reaction to it drops off precipitously when we pass it.See Table 6 of Rozin et al. (2013). They report, “A substantial proportion of individuals, in accord with a benign masochism prediction, report that their favorite level of an originally negative activity is just below, in intensity, a level that is not tolerable” (p. 445).

Consuming spices might have some ill effects, including inflammation.Nilius and Appendino (2013).

The amount of spicy food one has when young, especially between five and nine years old, affects preferences when one is older.See Siebert et al. (2022) for an excellent recent review of this literature. They conclude that changes in preferences might come in as early as two or three years old. Their broad conclusion (p. 12) is as follows: “Collective findings support that exposure to chili pepper in childhood promotes a preference for it.” More broadly, they conclude (p. 1) that there are “five determinants of chili pepper preferences: culture, exposure, gender, genetics, and personality.”

Feel 26: Fun and Excitement

Japanese macaques (Macaca fuscata) have been recorded jumping from a height into a perilously narrow water-filled trough.You can see a video of this: https://www.youtube.com/watch?v=Kb0XR3_obJ4&ab_channel=BBC.

The real question is, “Why is jumping into a trough fun for Japanese macaques?”See Balkaya and Catak (2016) for a similar exposition of this issue. They write that “no substance, activity, or stimuli is intrinsically pleasurable or rewarding unless the specific brain circuitry is hardwired to react to it and generate the feeling of pleasure” (p. 22). I’m not sure I agree with the term “hardwired” in that sentence, but otherwise our views are in accord.

In the human case, I like the way two scholars posed the question in a book on “gamer psychology”:Balkaya and Catak (2016), p. 22.

There is limited theorizing about fun from an evolutionary perspective,Balkaya and Catak (2016) note that “it has proven difficult to ascertain the adaptive value of play in nonhuman animals” (p. 25).

There is limited theorizing about fun from an evolutionary perspective, and hardly any scholars take aim at this question.Balkaya and Catak (2016) is an exception. Chick (2001) is another important exception and provides three explanations: physical training, social training, and cognitive training. There are echoes of this view in the approach I take here.

And many if not most fun activities are byproducts: like artificial sweeteners, they tickle our reward systems without providing the actual outcome for which those reward systems were designed.Balkaya and Catak (2016) conclude that “we play games because games trigger the very same motivations and offer the same ‘objects of desire’ that we experience and pursue in our ‘real’ daily life” (p. 29).

Class: Safe Practice Humans, like other animals, improve their skills with repetition.This idea is well supported by the large literature in behaviorism.

One wants to learn from one’s mistakes in, say, hunting, warfare, and dancing when there is no prey to be frightened off, no foe to fight back, and no audience to judge.There is a puzzle within this puzzle. “Practicing” hunting and warfare—sports—is fun, but practicing, say, chord progressions on a guitar, is not. I leave this as an exercise for the reader.

…and excellent work looking at the cross-culturally common practice of playing “monster,” in which little kids pretend an older sibling or adult is a monster, from whom they flee, often accompanied by raucous laughter.Steen and Owens (2001).

The market for video games has exploded, from a few billion dollars in the 1980s to hundreds of billions today.This information is available on, for example, Statista: https://www.statista.com/topics/868/video-games/.

Evidence from neuroscience shows that playing against a human rather than a computer produces greater activation of the reward circuits.Kätsyri et al. (2013).

I suspect that something like this might explain roller coasters, but that is sufficiently speculative that I’m going to relegate it to an endnote.Maybe riding a roller coaster signals that you’re brave? I alluded to this when I discussed my trip to Hershey. But plenty of people enjoy going on thrill rides when they are alone. Maybe our evolved psychology thinks it’s learning on a roller coaster in the sense that your visual system is getting a ton of data in a short period of time. By moving fast—and in odd directions—you’re getting sensory input at a tremendous rate. Even that tentative suggestion is suspect because you still enjoy the ride if you close your eyes and plug your ears. There is something about the speed and g-forces in themselves that seems to be enjoyable. Also, not for nothing, but there are videos of dogs on the internet that make it look like some of them, at least, enjoy going down slides. I’d love an explanation for that as well.

Unlike nearly all other species, humans cooperate in non-kin groups in intergroup conflict.There are many claims bundled into that sentence. For an excellent account from the perspective of the history of warfare, see Keeley (1996). On the evolutionary side, see, among others, Bowles (2009). See especially Tooby and Cosmides (2010).

One proposal is that dancing in groups evolved to signal to others that one’s group is well-coordinated, a kind of formidability display.Hagen and Bryant (2003). On the formidability claim, see Fessler and Holbrook (2016). For more recent work on dance and signaling, see Mehr et al. (2021) and Hagen (2022). Dancing by oneself doesn’t fit this model, and it’s plausible that dancing might also signal individual qualities, such as dexterity and vigor. See, for instance, Fink et al. (2021).

As for our macaques, some species of primate have been observed jumping into water to evade terrestrial predators.Blaszczak-Boxe (2016). Meet the aquatic monkey with a love of diving and swimming. New Scientist. Retrieved on 12/4 from https://www.newscientist.com/article/2074675-meet-the-aquatic-monkey-with-a-love-of-diving-and-swimming/.

Feel 27: Orgasm

So it’s pretty clear what orgasms measure and motivate.I thought this was uncontroversial. Fleischman (2016) writes, “I will argue that intense sexual pleasure, especially orgasm, can be understood as a primary reinforcer shaped by evolution to reinforce behavior that facilitates reproductive success (i.e., conception through copulation)” (p. 1). The fact that she says that she will “argue” this point suggests to me that she felt it was controversial.

Some people never experience orgasm.IsHak et al. (2010) indicate that up to 30% of women in some samples report that they never have an orgasm during sex. Perhaps surprisingly, Jenkins and Mulhall (2015) report a similar number regarding men, indicating “that only 25% of males routinely achieve orgasm in all sexual encounters.” (See Section 4, Prevalence.) Inability to achieve orgasm is the second most common sexual complaint among women, following hypoactive sexual desire disorder (IsHak et al., 2010). I note that sources for this feel are less current than for some others. The body of research on sex and sexuality is somewhat thin, perhaps because of the stigma associated with sex in general and sex research in particular. The Kinsey Institute at Indiana University is an excellent source of information. Consider that as recently as 2016, Dawson et al. (2016) wrote, “Little research has been conducted to examine paraphilic sexual interests in nonclinical samples” (p. 20). That is, less than ten years ago, there was “little research” on what turns people on outside of people involved in mental health clinical settings. For those interested in data on sexuality, I highly recommend a Substack called Knowingless, by Aella, who does excellent work on sex and sexuality unburdened by institutional review boards.

Some people enjoy orgasms after only modest stimulation.Althof (2006) concludes that the rate of men who suffer from premature ejaculation and related conditions is between 20% and 30%.

Indeed, the specific stimuli that arouse men are tremendously, even puzzlingly, variable.The list of so-called paraphilias—conditions in which someone requires specific textures, objects, or situations for sexual enjoyment—is lengthy, including exhibitionism, sadism, voyeurism, and so on (Dawson et al., 2016). By and large, paraphilic interests are more frequently admitted by men than by women (e.g., Fisher, 2023; Dawson et al., 2016). One community estimate is that 64% of men report some degree of arousal to at least one paraphilic stimulus (Ahlers et al., 2011). Dawson et al. (2016) present a dataset showing robust sex differences: Among women, the highest-reported paraphilic interest was voyeurism.

This requirement for rhythmic pressure on the penis is explained by the pressure a vagina exerts on a penis when a male is thrusting.For a thorough recent account of the physiology of male sexual arousal, see Bogacki-Rychlik et al. (2024).

This last part is important because there are large differences in fertility depending on age.Fertility—the chance of conception conditional on insemination—is highest for women in their early twenties and then declines, reaching zero after menopause.

There has been some speculationWheatley and Puts (2015).

One suggestionSymons (1981).

Geoffrey Miller offers an alternative explanation,See Geoffrey Miller’s The Mating Mind. See also Puts et al. (2012), who suggest, “Female orgasm may have evolved to function in sire choice by increasing the probability of fertilization from high quality males,” finding that “[w]omen reported more frequent orgasm during or after male ejaculation when mated to attractive men.”

In addition, whether or not the male can produce an orgasm informs a woman of his skill and interestThere is evidence that orgasm increases with foreplay (Singh et al., 1998).

Psychologist Diana Fleischman argued that orgasms also act as a signal, indicating “devotion, vulnerability, and malleability.”Fleischman (2016), p. 1.

Feel 28: Love (Romantic)

I like the way that Dorothy Tennov discussed it, using her term “limerence.”Tennov (1998).

As Steve Pinker put it, when you’re on the mating market, you’re not looking for the best of all possible mates; you’re looking for “the best-looking, richest, smartest person who would settle for you.”This line appears in an article by Steve Pinker in Time entitled “Crazy Love.”

Robert Frank suggests an answer in his book, Passions Within Reason.Frank (1988).

Feel 29: Love (Family)

In some species, such as fish, parents produce a ton of offspring, but the investment is limited to the supplies in the egg.See Trivers (1972) for classic work on parental investment. In multiple species, the parent dies at the moment of reproduction, as in the case of salmon spawning.

This fact explains why parents take extreme risks, endure unending suffering, and even make the ultimate sacrifice on behalf of their children.Classic sources include Clutton-Brock (1991), Hrdy (1999), Williams (1966).

Human infants are born singularly unable to survive without help.Clutton-Brock (1991).

Anthropological evidence suggests that in most human cultures—just as in many bird species and some mammals—both the males and the females invest: Paternal love is among the most powerful feels as well.See, for example, Geary (2000).

The love of a child for a parent should be expected to be—and often is—as profound as the love of a parent for a child.I don’t think this is especially controversial, but for excellent work on the child/parent relationship, see, for instance, Hrdy (1999). See also Bowlby (1969), Konner (2010), and Rosenblatt (2003).

Recall from your reading of Richard Dawkins’ The Selfish Gene that a gene can help itself get into the next generation in two ways.If you haven’t read it, run don’t walk and do so. Or The Extended Phenotype.

A gene in me has a 50/50 chance of also being in my sister because of the way that sexual recombination works.Kurzban et al. (2015); West et al. (2007b).

…that one organism can increase its fitness by helping a relative in his famous formula, C < rB, where C is the cost, B is the benefit, and r is the coefficient of relatedness.Hamilton (1964).

And, indeed, anthropological evidence suggests that, just as in the case of many of our mammalian relatives,Clutton-Brock (1991).

And, indeed, anthropological evidence suggests that, just as in the case of many of our mammalian relatives, human females across cultures provide more care to children than fathers.See Whiting et al. (1988) for classic work.

For dads, paternity is often at least a little uncertain.Kurland and Gaulin (2005) estimated that paternity certainly is, on average, about 90%.

In cases in which he cannot be certain of fidelity, he might be less inclined to invest.Alexander (1974); Anderson et al., (2007); Clutton-Brock and Parker (1992); Geary (2000).

This fact helps to explain why in many different contexts, females—and their families—go to great lengths to assure a mother’s partner that he is in fact the biological father.Daly and Wilson (1982); Wilson and Daly (1992).

While of course many stepfathers love their stepchildren, Daly and Wilson argued that the love of biological parents is a strong force protecting young from harm.Daly and Wilson (1985); Daly and Wilson (1988); Daly and Wilson (1996).

Ultimately, even a mate often is a lower priority than a child, as many new parents rediscover.Burnstein et al. (1994); Madsen et al. (2007); Salmon and Shackelford (2011).

The relentless logic of natural selection has made us all natural nepotists.Hrdy (1999).

But when we said the people on the tracks were their brothers, about half of the people in our study said they would push someone in front of the trolley,Kurzban et al. (2012). See also Bleske-Rechek et al. (2010) and Oda (2013).

Cousins, grandparents, and more distant relations love one another too.Coall and Hertwig (2010); Michalski and Shackelford (2005).

For better or worse, love depends on how many people need it.Trivers (1974).

This fact leads to disagreement about the division of resources, creating sibling rivalry.Trivers (1974).

Feel 30: Grief

…that like so many feels, grief remained something of a mystery: “Despite over a century’s worth of empirical research,” they wrote, “little is known about the conditions that alleviate or exacerbate aspects of grief.”White and Fessler (2018), p. 40. O’Donnell et al. (2025) more recently made a similar remark (p. 3), that “consensus on the components of an adaptive grieving process for both death and non-death losses remains elusive.”

Not everyone goes through those stages, and they don’t always go in the same order.Stroebe et al. (2017). Reynolds et al. (2020) suggest that grief still “proceeds in stages.”

Still, grief is greatest for the largest fitness losses, especially a child.White and Fessler (2018).

Grief typically manifests as very deep sadness, a loss of interest in activities that one would normally seek, persistent thinking about the loss, and changes in appetite and sleep patterns.Andrews et al. (2021).

Generally, scholars have found that in the few months following the loss, people are vigilant for signs they are still around, poised to see their face one last time.White and Fessler (2018).

Is this some sort of bug, a kind of wishful thinking?Generally, until relatively recently, grief was understood as a byproduct of the attachment system rather than an adaptation with its own distinct design features.

Research shows that people who feel grief often build counterfactuals.Davis et al. (1995).

The sadness of grief, which is often accompanied by withdrawal from other pursuits, provides the time to think about this crucial issue.Andrews et al. (2021).

The sadness of grief has a related function: motivating taking the time to make adjustments given one’s new circumstances.O’Connor and Seeley (2022).

…of a partner, close friend, or ally means that it’s important to update where one stands in the social world and consider carefully how to reallocate time and effort to rebuild one’s social network.Huron (2018).

These are signals that let others know that one has suffered a profound loss and might benefit from additional support.Huron (2018).

In Sociopath: A Memoir, Patric Gagne—author and self-diagnosed sociopath—shows no emotion when her pet ferret dies during her childhood.Gagne (2024).

The sadness we show when we are grieving signals to others that we are in need of help,Andrews et al. (2021).

Some scholars have argued that this is the principal function of guilt, to show others one’s capacity for love and depth.Winegard et al. (2014).

The idea was that the psychological price of building strong feelings for others was the pain when the relationship was gone.Andrews et al. (2021).

Feel 31: Missing Someone

The greater the benefits that we are not getting from someone else, the sharper the pain.For other feels, this endnote is where I would cite the scholarly literature and credit this idea. Somewhat to my surprise, I cannot find this idea anywhere in the journals. Most of the work on the topic of separation seems to be in the literature on separation anxiety, both in children and adults. This is another feel for which I’m mostly just providing my best guess, given the dearth of work in the area. Jiang and Hancock (2013) write, “The prevalence of [long distance] relationships, however, is not well reflected in communication or other social science studies. This domain is poorly understood…But…scholars firmly believe that geographic proximity and frequent face-to-face (FtF) contact are necessary for developing mutual understanding, shared meanings, and emotional attachment in romantic relationships” (pp. 556–557).

For parents, helping offspring yields net evolutionary benefits, so separation blocks both receiving and delivering benefits.This view predicts that parents will especially miss offspring during times when investment can do the most good at the least cost. I don’t know of tests of this claim.

A lover might stray,See, broadly, Platek and Shackelford (2006).

While the research on long-distance relationships has yielded some contradictory findings,See, for example, Kelmer et al. (2013).

While the research on long-distance relationships has yielded some contradictory findings, people in such relationships tend to prioritize communication with one another and working to achieve intimacy more than couples not physically separated.Jiang and Hancock (2013).

Indeed, frequent, responsive contact, such as texting, predicts greater satisfaction with the relationship.Holtzman et al. (2021).

Some research on long-distance relationships has, intriguingly, shown that relationship stability, satisfaction, and trust are no worse than found in couples not living apart,Jiang and Hancock (2013).

This might include making oneself more attractive, derogating potential rivals, or perhaps, penning protestations of pure passion in purple prose.See Dillon et al. (2014) for cross-cultural data and an excellent review of the mate-guarding literature to that point.

This sort of anxiety from separation is normal, but it can reach clinical levels even in adults, perhaps around 5% of the population according to one estimate.Shear et al. (2006). This work is somewhat old but includes a large sample, making it a good estimate.

Feel 32: Aroused (Sexually)

For the present purpose, the moral of this story is that sexual attraction, born of divine intervention or mundane natural selection, is a powerful force.Fisher (1998) breaks emotions into three categories: sex drive, attraction, and attachment. For brevity, I omit such useful nuances. Note that in this chapter, I am referring to a vast literature and therefore am neglecting to cite important contributions. Citations should be thought of as entry points into each literature.

For a female, the cost might include losing a reproductive cycle, carrying a non-viable embryo to term, or worse.Trivers (1972). A key issue is parental investment. In many animals, female parental investment is much greater, making a mistake, everything else equal, more costly.

Because mate choice is of such great moment, humans have an intricate set of systems designed to assess the value of a potential mating opportunity.Buss (1989).

Entire books have been written on this topic,See especially The Evolution of Human Sexuality by Don Symons and The Evolution of Desire by David Buss. See also Justin Lehmiller’s The Psychology of Human Sexuality.

The first task evolution needs to solve is piquing your sexual interest only for those individuals who are of the same species, of the opposite sex, and have reached but not exceeded reproductive maturity.These claims are obviously just to do with the chances of successful reproduction. As elsewhere, I am making no claims about morality or ethics. See Buss (1989) and the books in the prior note for additional work.

However, because chronological age itself isn’t directly visible, this assessment is based on cues that correlate with fertility.Sugiyama (2005).

…has confirmed that humans are, on average, sexually attracted to people who have secondary sexual characteristics, such as those to do with body shape, skin, teeth, hair, and other traits that change with age.Grammer et al. (2003); Kenrick and Keefe (1992).

People’s attention is drawn to certain body parts more than others—biceps and breasts more than shoulders and pinkiesSugiyama (2005).

People’s attention is drawn to certain body parts more than others—biceps and breasts more than shoulders and pinkies—and people who have the cues of being sexually mature are the most sexually arousing.Sugiyama (2005); Conroy-Beam and Buss (2019). For early accounts, see Ellison (1994) and Kenrick and Keefe (1992).

This relationship explains why men tend to be most aroused by women in their early twenties, the ages of maximal fertility.See, e.g., Hawkes and Smith (2010), Figure 1.

Indeed, cues to women’s age are a powerful predictor of men’s ratings of sexual attraction.Buss and Schmitt (2017).

In contrast, women tend to seek partners who can provide not only viable sperm but also support and protection, which often translates into preferences for men of their age or slightly older than themselves.The literature on age is complex. For two good sources, see Bleske-Rechek et al. (2009) and Conroy-Beam and Buss (2019).

Context can inhibit arousal, such as being in a workplace.See Janssen et al. (2000). So-called controlled processes, including concerns about norms, can influence sexual arousal.

Other factors, such as cues to kinship,See Deb Lieberman’s excellent work on this topic, such as Lieberman et al. (2003).

Anything from smooth skin to signs of intelligence to skilled movements to demonstrations of creativity provides important information about whose genes would be good to combine with one’s own.See Geoffrey Miller’s The Mating Mind (2001), still the best treatment of this topic.

We spend a lot of time looking at faces, in which we can see cues to age, health, and genetic quality.Little et al. (2011); Thornhill and Gangestad (1999).

The success and profitability of media that provide men visual stimulation of sexually attractive and receptive others is evidence of its effectiveness.Salmon et al. (2019); Malamuth (1996).

Even aromas can lead to sexual arousal, particularly if they evoke memories of past partners or experiences.See, for example, Hoffmann et al. (2012) for some provocative empirical work on this topic. See Snowdon et al. (2006) for discussion and evidence of the role of olfactory sensations and sexual arousal in non-human primates as well as humans.

Some people are aroused by certain textures, others by particular shapes, still others by particular kinds of behavior.See especially research on the paraphilias. Wiederman (2003) provides an overview.

Feel 33: Liking as a Friend

What are friends for?Well, really the genes. In cases such as this one, I’m simplifying. See The Selfish Gene or, better, The Extended Phenotype. This chapter views friends as part of the extended phenotype of humans. See DeScioli and Kurzban (2009) for the genesis of the view described here.

As a team of biologists recently put it, “Male bottlenose dolphins form persisting multi-level alliances…to sequester females during consortships.”Gerber et al. (2021). They write, “Male bottlenose dolphins form persisting multi-level alliances. Second-order alliances of 4–14 males are the core social unit, within which 2–3 males form first-order alliances to sequester females during consortships” (p. 1).

Holding aside blood relatives—often chosen as best man to avoid revealing one’s best friendDeScioli et al. (2011).

This reciprocal relationship was stronger than factors, including age, gender, geography, popularity, and so on.DeScioli et al. (2011).

For more distant friends, we are less inclined to do so.Delton and Robertson (2016) refer to this as a “welfare tradeoff ratio,” which is more precise but more of a mouthful.

In terms of the former, humans care a great deal about where they rank because friends are allies who choose sides when conflicts emerge.These ideas were developed in concert with Peter DeScioli. See DeScioli and Kurzban (2009b), DeScioli and Kurzban (2012), and DeScioli et al. (2011).

…experience as “liking” for a friend is a summary measurement of where the person is in your queue—and therefore how likely you are to support them—and your willingness to bear costs to help them.I’m putting this relatively baldly here. Friendship is complicated and, in my view, under-theorized.

Helping your friend succeed benefits you indirectly because part of their success will be channeled toward you: Increasing their power and status, for example, means they can give you more benefits in the future.The finding that spending money on other people makes the spender happy seems to be one of those rare findings that might survive the replication crisis (Aknin et al., 2022).

Feel 34: Empathy

Psychologists have struggled to define empathy.See, for example, Wispé (1986) or, more recently, Zaki (2014).

Now, some scholars distinguish between the sharing of the feeling on the one hand and understanding the feeling on the other.There are different schools of thought. Empathy has been discussed as having a number of distinct or at least distinguishable components, including sharing feelings of another person, taking another person’s perspective, and having compassion for another person. See Ferguson et al. (2021) for a good, recent discussion. See also Batson (2010). For a thorough treatment, see Paul Bloom’s book Against Empathy.

Like Paul Bloom, if I had to be concise, I think about empathy as “feeling the feelings of other people.”Bloom (2016). Batson and Ahmad (2009), for example, define it as “feeling for another person who is in need” (p. 144).

Empathy, under the right circumstances, motivates altruism, which, in many circumstances, will be repaidSee Eisenberg and Miller (1987) for a classic formulation.

Empathy, under the right circumstances, motivates altruism, which, in many circumstances, will be repaid or, if not, might at least boost one’s reputation.See, for example, Ferguson et al. (2021), who write, “Our interest in being known as empathetic makes good evolutionary sense: Engaging in empathy is a sign of willingness to act prosocially and of our value to those around us. If we cultivate a reputation as empathic and attuned to the needs of those around us, the chances of others’ supporting us in a time of need are higher” (p. 126).

One of the best-documented circumstances has to do with group membership: We feel less empathy for “others,” people who are not in the groups with which we ourselves identify.See, for example, Gutsell and Inzlicht (2010).

Empathy also is blocked when we see our ability to help as unlikely to make a difference.Goetz et al. (2010) found that people feel compassion less if they don’t think that they can help in a way that will make a substantive difference.

In addition, excellent work by Phil Tetlock and his former student Katrina Fincher illustrates that seeing someone as morally culpable short-circuits empathy, leading to dehumanization.Fincher et al. (2017).

Related, research suggests that the inclination to help declines if we view the target as responsible for their suffering.See, for example, Decety et al. (2010), who found that “the more participants blamed…targets, the less pain they attributed to them as compared with healthy controls” (p. 985). If subjects think that a target is responsible for their predicament, they suspend empathy. Similar results can be seen, for example, in the literature on HIV/AIDS. People are more compassionate in cases in which the disease was contracted through a transfusion compared to other means. See, for example, Weiner et al. (1988).

I leave this vexing question to the reader.See Peter Singer’s work, especially Singer (2015), for an excellent treatment.

Feel 35: Compassion

In evolutionary biology and later across the social sciences, the prisoner’s dilemma game was used as a very simple way to model this type of interaction.For early work, see Rapoport and Chammah (1965). Other work cited in this chapter follows in this tradition, especially Trivers (1971) and Axelrod (1984).

However, if players repeat the game over time, they can establish a pattern of responding to cooperation with cooperation, making both better off.Axelrod (1984).

Many have argued that this pattern, called reciprocal altruism—not all that different from the golden rule—is an integral part of human psychology.See Axelrod (1984) for a classic account. See also Robert Wright’s book Nonzero. Many more sources are available on this idea, too many to document. Many strategies other than the classic “tit-for-tat” strategy discussed by Axelrod have been shown to be stable. See, for instance, Nowak and Sigmund (1993).

Related, bear in mind that empathy often feels unpleasant—feeling another’s pain—whereas compassion typically feels pleasant, rewarding.Bloom (2017), discussed in the prior chapter, also distinguishes between the two. Singer and Klimecki (2014) similarly draw the distinction and provide evidence from the perspective of neuroscience.

So if you’re successful this week, that doesn’t guarantee you will be successful next week.See, for instance Hill and Hawkes (1983) for classic work. See more generally the literature on hunting and research by Kim Hill, Kristen Hawkes, Hillard Kaplan, and their collaborators.

Further, when a hunter was successful, there was the very strong possibility that whatever they succeeded in taking would become inedible before they and their family could consume all of it.See the classic work by Lee and DeVore (1968). This research has obviously expanded since.

Most people do.For data, see Cashdan (1980), de Waal (1996), and Kaplan and Hill (1985).

We feel compassion when we see someone who could benefit from our largesse.Trivers (1971) made this argument, using the word “sympathy” instead of compassion, writing that the emotion “has been selected to motivate altruistic behavior as a function of the plight of the recipient of such behavior…even to strange or disliked individuals” (p. 49). Darwin, in The Descent of Man, made a similar argument, though he relied on an argument today that would be viewed as group selection as opposed to reciprocal altruism.

Research using brain imaging shows that viewing others’ suffering activates regions such as the anterior insula and anterior cingulate cortex, areas linked to empathy and social emotions.Lamm and Singer (2010).

Crucially, remember that evolution demands that we be discriminating.See, for example, Goetz et al. (2010).

…to contribute in the future, either because of a lack of ability to do so (e.g., they are quite far gone) or a lack of interest in doing so (because they are selfish, etc.).See Goetz et al. (2010), especially p. 357, for a discussion of empirical evidence.

Other research has found, along similar lines, that people experiencing uncontrollable misfortunes (e.g., cancer patients) elicit stronger feelings of pity and compassion compared to those perceived as responsible for their circumstances (e.g., substance abusers).Weiner et al. (1988).

If a person asking for aid is seen as responsible for their condition and unmotivated to try to alleviate it themselves, people are less likely to feel compassion and more likely to feel anger.See Petersen et al. (2012) for an excellent and thorough discussion, along with interesting data to do with support for social welfare policies. See also Delton et al. (2018).

The motivation is altruism,Goetz et al. (2010), p. 355.

The motivation is altruism, investing in other people,Petersen et al. (2012), p. 398

The reverse holds as well: People who see welfare recipients as needy and deserving of help feel compassion.Petersen et al. (2012); Delton et al. (2018).

The literature in psychology suggests that a key additional element is that the person feeling compassion has to feel that they have the capacity to help.Goetz et al. (2010) write (p. 358) that “a sense of self-efficacy in aiding those who suffer increases the likelihood of experiencing compassion, presumably because individuals feel that their personal resources match the demands of the situation.”

When their time came, they metamorphosedThis story appears in Ovid’s Metamorphoses.

Feel 36: Grateful

Like many feels, gratitude went under the radar for a long time, with one prominent researcher claiming that “psychological science largely neglected gratitude until the 21st century.”McCullough et al. (2008), p. 281. Note that Robert Trivers, in his seminal work on reciprocal altruism in 1971, proposed that gratitude was designed around mutually beneficial exchange.

Much ink has been spilled talking about gratitude, especially as it relates to happiness.See, for example, Robert Emmons’ book Thanks! How the New Science of Gratitude Can Make You Happier or Marty Seligman’s book, Flourish, which discusses gratitude at some length. See also, for instance, Wood et al. (2010).

As some prominent scholars in the area put it, “Gratitude is an affective readout that alerts people that they have benefited from another person’s prosocial behavior.”McCullough et al. (2008), p. 281.

If you are walking to work through fresh snow and you clear a path, incidentally making my own trek easier, I haven’t really learned anything about your intentions toward me.I drew this example from Williams’ book Adaptation and Natural Selection, in his discussion of foxes leaving a trail in the snow.

To evoke gratitude, the help I get from you must be intentional: I feel gratitude toward your benevolence, not accidents.See, for instance, Tsang (2006).

This analysis also explains, somewhat sadly, why people tend to be less grateful when family members help them.Bar-Tal et al. (1977).

…lines, help given at a crucial moment, even if the help represents a small cost to the giver—a modest amount of food means a great deal to someone who is starving—can trigger enormous gratitude.Tooby and Cosmides (1996).

Gratitude keeps ongoing cycles of reciprocal benefits in motion.Trivers (1971).

It’s not all for naught: For example, research shows that simply adding “thank you” to the check at a restaurant increases tips.McCullough et al. (2001).

Interestingly, there is evidence that gratitude motivates not only returning the favor in particular but also being more generous in general, though this more general desire is weaker.Ma et al. (2017).

When someone helps us and we believe that the motive is mostly to do with that person’s expectation that we will reciprocate, we’re more likely to feel an unpleasant sensation, obligation, rather than gratitude.Watkins et al. (2006).

Feel 37: Pleasure From Helping

It’s thanks to your support that I’ve been able to make it to this moment, and I’m forever grateful.”I mention this story in the post on The Living Fossils called “Warm Fuzzies.”

To be sure, being nice does feel good.For a review of the literature to that point, see Aknin et al. (2018).

Research reliably shows that people experience pleasure—economists call this feeling a “warm glow”Andreoni (1990).

While we all are, of course, more or less at least somewhat selfish, a frequently replicated finding across cultures is that people get more happiness from spending money on others than on themselves.See, for example, Aknin et al. (2013). See also Dunn et al. (2014).

The joy of giving has been measured in laboratory settings in children as young as 5 years old.Fast et al. (2023).

Children are happier when they see a recipient’s positive reaction, even if their intent to help is thwarted.Fast et al. (2023).

It really is the thought that counts.Bianchi et al. (2023), Study 2.

Work in neuroscience confirms that giving money to others activates the parts of the brain associated with reward.Harbaugh et al. (2007).

The experience of pleasure from helping can occur if the recipient doesn’t even know it was you who delivered the aid.Andreoni (1990).

People can feel happy or joyful when good things happen to close friends and loved ones, a phenomenon referred to as “compersion” by some, “symhedonia” by others, and mudita by Buddhists.Aron et al. (2004). Compersion: Balzarini et al. (2021). Symhedonia: Royzman and Rozin (2006).

As the journalist Damon Runyon put it, “Always try to rub up against money, for if you rub up against money long enough, some of it may rub off on you.”This line appears in the short story, A Very Honorable Guy. The quote is documented here: https://en.wikiquote.org/wiki/Damon_Runyon.

Additional benefits of helping have to do with the other person’s knowledge that you were the one who provided the help, which explains why altruism is only rarely truly anonymous.Even anonymous donations to charity are not necessarily anonymous. Donors often find ways to let their friends know that they made the anonymous donation, allowing them to enjoy the reputational benefits. An excellent analysis by Harbaugh (1998) suggests that donors tend to contribute just enough money to get into the category advertised by the recipient (such as “Patron” or “Saint”). This pattern implies that donors want the reputational benefit at the lowest possible price.

When someone helps us, we are inclined to return the favor and vice versa.See Trivers’ (1971) theory of reciprocal altruism.

Now, it’s true that close friends generally don’t make these exchanges explicitSee Fiske (1992) for classic early work on this topic. For a compatible view from economics, see Smith (1998).

…it’s true that close friends generally don’t make these exchanges explicit—a good friend doesn’t leave cash when you make them dinner—but people do remember the help others have rendered and seek to repay it.See, for example, McCabe and Smith (2001).

…think of you as hard to replace because of the special ways you improve their lives, well, that’s good for you, and they’re likely to help you, especially when you need it the most.Tooby and Cosmides (1996).

So the warm feeling you get from being helpful is also measuring the benefit of the change in how others view you, explaining why very public acts of altruism are especially rewarding.Smith and Bliege Bird (2005). Barclay et al. (2021).

…to get that reward of the warm glow again by a similar route: Research supports the view that people who experience the pleasure of giving to others report being motivated to do so again.Bianchi et al. (2023). For a review, see Aknin et al. (2018).

Interestingly, a good predictor of how much time people spend volunteering is a person’s sense of their own well-being.Thoits and Hewitt (2001).

…the laboratory, when researchers put participants into a good mood—by getting them to think happy thoughts or giving them money they weren’t expecting—those participants tended to be more generous with their time and effort.See Aknin et al. (2018) for a discussion and additional citations.

Feeling good makes people altruistic and being altruistic makes people feel good.Aknin et al. (2018), p. 55.

As the philosopher Immanuel Kant put it, “Whoever makes himself a worm cannot complain when he is then trampled underfoot.”Kant (1797/1996). This quotation is translated from the German. Renderings vary.

Altruism is a subtle game, and humans are picky about how we direct our prosocial efforts.Bloom (2016, 2017).

Feel 38: Trustful and Distrustful

Humans are irretrievably social.Dunbar (1998); Tomasello (2009).

The competitive process of evolution by natural selection ensures that other people are a source of both help and harm.See especially Cosmides and Tooby (1992) and subsequent work on social exchange and cheater detection.

While cooperating with other people holds the possibility of making great gains, it poses risk.Axelrod (1984); Nowak (2006).

The adaptive problem surrounding the feeling of trust, then, is figuring out if one should expose oneself to harm or exploitation now given the possibility of benefits, usually to be had later.See Simpson (2007) for an excellent treatment. I note that, once again, scholars claim it is under-studied. Simpson writes, “Despite its great theoretical importance, a limited amount of research has examined how and why trust develops, is maintained, and occasionally unravels in relationships” (p. 264).

If I give you my money today, if you don’t return it along with the interest you owe me, I’m worse off than I would have been.See, again, Trivers (1971) and Cosmides and Tooby’s work on cheater detection, such as Cosmides (1989) and Cosmides and Tooby (1992).

…that the history that we have with someone heavily influences how likely we are to extend trust to them: The more they have been trustworthy in the past, the greater our feelings of trust.For example, see Lewicki and Bunker (1996) and McKnight et al. (1998). Another good source is Kevin McCabe’s work on “goodwill accounting.” See, for instance, McCabe (2005) and McCabe and Smith (2001).

Certain faces just look more trustworthy than others.Oosterhof and Todorov (2008); Todorov et al. (2015).

Similarly, we pay attention to little bits of others’ behavior, including eye contact, often building our judgments of whether or not someone is trustworthy in a fraction of a second.The recent increase in virtual meetings has sparked additional attention on eye contact. See, for instance, Fitzpatrick and Tickle (2025) for a recent study illustrating the effects of eye contact. See, for example, Kaisler and Leder (2016) and Bayliss and Tipper (2006) for some work on eye gaze and trustworthiness. See Kurzban (2001) for some of my work that touches on this topic, investigating if eye gaze increases cooperation. For research on rapid judgments, see Willis and Todorov (2006) and Ballew and Todorov (2007).

…use people’s group membership as part of these decisions, too: Is the other person a member of my group, or are they a member of a group that I view as, overall, generally trustworthy?See, for example, Brewer (1999) and especially Stürmer and Snyder (2010) for a good review of work to that point.

For instance, people trust members of certain religious communities, such as Christians, more than others.McCullough et al. (2016).

Similarly, what we know about a person’s interactions with others—their reputation—affects our feelings of trust.Nowak and Sigmund (1998). See also Fehr and Fischbacher (2004).

If we do feel sufficient trust, then the motivation is to take the risk, making ourselves vulnerable, usually in the service of some sort of cooperative enterprise.Simpson (2007).

…the gains from cooperating are so vast, a great deal of effort has been devoted to creating societies and cultures in which one can expose oneself to risk with much less concern about betrayal.North (1990); Ostrom (1990).

Indeed, trust is everywhere in the modern economy, allowing a tremendous array of transactions to occur that would not otherwise because of the risk to the first mover.See especially Fukuyama’s (1996) classic work on this topic, though many economists and historians have of course contributed to this literature.

Consider, too, all the ratings that we make use of for our purchases, drivers, service providers, and so forth.Most people are well aware of the pervasiveness of star rating systems and other reputation management systems. There is of course scholarly work on this, especially in the management literature. See, for example, Resnick et al. (2000) and Dellarocas (2003).

When these rules are very strong, imposing high penalties for violating the rules, people tend to conform to them.North (1990); Tyler (2006).

Feel 39: Depressed

Increased tolerance—the idea that certain kinds of behaviors are simply the result of different preferences—is one important force in these changes in points of view.See Steve Pinker (2012), his book entitled Better Angels of Our Nature.

This idea might seem difficult to entertain for depression or, as the Diagnostic and Statistical Manual would have it, “major depressive disorder.”The criteria for MDD in the DSM-5 include depressed mood, reduced interest in activities, fatigue, weight loss or gain, problems sleeping, and suicidal ideation. Not all need be present for the diagnosis.

According to this view, depression is, just like a strike, someone saying, “Matters are so serious that I am willing to bear costs unless I get more help from you.”The idea in this chapter was developed by Ed Hagen. Please see citations in the references section.

Physical assault, the death of a loved one, and divorce are all common antecedents of depression.See, for example, Devries et al. (2013).

Another important symptom of depression is thinking about death and considering—or attempting—suicide.Angst et al. (1999).

From the perspective of the father and her relatives, the mother’s death would represent a tremendous fitness cost.See Hagen (2002, 2011).

It’s important to reiterate that this approach to depression is relatively new and speculative.See Hagen (2002) and Hagen (2003).

In 2022, according to the CDC, roughly 3% of attempts resulted in death.Centers for Disease Control and Prevention (n.d.). Suicide facts. https://www.cdc.gov/suicide/facts/index.html.

Feel 40: Angry

One human defense is anger, a universal human emotion,Ekman (1973).

One human defense is anger, a universal human emotion, seen even among young infants,Stenberg et al. (1983).

One human defense is anger, a universal human emotion, seen even among young infants, which comes with its own distinctive facial expression.Sell et al. (2014).

The best account of anger, in my view, is known as the recalibrational theory,See, for example, Sell (2011), and Sell et al. (2017).

Research supports the idea that the less negotiating power one has, the less anger one feels.Sell et al. (2009).

While this effect isn’t observed for women, interestingly, more attractive women are more prone to anger than less attractive women.Sell et al. (2009).

In other cases, you might offer an analysis: People often refer explicitly to the size of the benefit to the person who did the harming.Sell (2011).

This aspect of anger explains why violence motivated by anger is often more of a display than an attempt to do real bodily harm.Sell et al. (2017). They write (p. 111) that “anger-based aggression typically appears designed to recalibrate the target rather than incapacitate or kill.”

The body is preparing for vigorous activity, increasing heart rate, breathing rate, and so on.Sznycer et al. (2022).

Apologies often, but not always, end conflicts because they indicate to the angry person that their signals have been successful.McCauley et al. (2022).

(Note on the chapter “Angry” as a whole)See, for example, Sell et al. (2017).

Feel 41: Envious

You shall not covet your neighbor’s wife, nor his male servant, nor his female servant, nor his ox, nor his donkey, nor anything that is your neighbor’s.”This is the tenth commandment, Exodus 20:17. Translations vary; this one is from the World English Bible, which is in the public domain.

Say what you want about the seven deadly sins—pride, wrath, sloth, and so on—but only envy makes it on the list of the Big Seven and earns a spot in the Big Ten.Van de Ven (2016), I discovered, made a similar observation. Nothing new under the sun. See also Silver and Sabini (1978) for a classic and excellent treatment.

Genes that did not motivate behavior to obtain the ingredients of reproductive success—food, status, good mates—from others would be at a selective disadvantage compared to ones that did.Like so many feels in this book, there is somewhat surprisingly little research on the topic.

The unpleasant feeling that accompanies such observations is the measurement that one is behind in the competition for status, resources, or mates.S. E. Hill and Buss (2008) provide a good account.

We should similarly expect people to want—and be envious of—whatever it is that constitutes a route to reproductive success: skills, talents, abilities, and, of course, resources.Ramachandran and Jalal (2017). See DelPriore et al. (2012) for a good study of what elicits envy, often to do with mating, resources, and status.

For example, people are more envious of someone described as “similar” to them than they are of Bill Gates,Ramachandran and Jalal (2017). This finding is based on a tiny sample. Still, it’s probably correct.

Instead, there is substantial evidence that people are envious when they compare themselves to others who are doing better in domains of personal relevance.Hill et al. (2011), p. 653, my italics. There are multiple definitions, for example, “an emotion which ‘occurs when a person lacks another’s superior quality, achievement, or possession and either desires it or wishes that the other lacked’” van de Ven (2016), p. 337, quoting Parrott and Smith (1993), p. 906.

In one study, people remembered the most information about the people they reported they were most envious of.Hill et al. (2011), Study 2.

If you can’t think, hey, it could have been me, you’re less likely to feel envy.Van de Ven and Zeelenberg (2015).

So if the feeling of envy measures the difference between what you’ve got and what a relevant other has—not just their stuff but the esteem in which others hold themSee Landers and Shaw (in press) for recent empirical work on this topic.

There’s a reason some scholars have referred to this pattern, harming rivals, as “malicious envy” (as opposed to “benign envy”Van de Ven (2016).

Indeed, research suggests that the benignly envious take positive steps, such as setting more ambitious goals, studying more, and working harder.Van de Ven et al. (2011).

…to what many economists take to be wasteful signaling, as the wealthy strive to show off that they have won the status game by buying ever bigger yachts, faster cars, and increasingly bejeweled accessories.See Robert Frank’s work, especially Luxury Fever (2001), for an excellent account. As with so many things, Adam Smith got there first. See The Theory of Moral Sentiments, where Smith talks about “our disposition…to imitate the rich and the great…” (p. 61).

Related, feelings of envy can, for better or worse, influence support for public policies that enact Robin Hood, taking from the rich and giving to the poor.Sznycer, Lopez Seal, et al. (2017).

Even people with massive amounts of resources feel the pull of envy and, motivated by this emotion, spend time and treasure in competition with other people with massive amounts of resources.See, to take just one example, Sowell (1995).

The tide might have lifted many boats, but even the super-rich still care about whose boat is biggest.See Evan Osnos’ recent book, The Haves and Have-Yachts for a compelling account.

Feel 42: Jealous—Romantic/Sexual

…another fatality to jealousy, killed when he got home by his wife, Clytemnestra, angry that Agamemnon had sacrificed their daughter, Iphigenia, as well as jealous that Agamemnon had brought home Cassandra as a concubine.See especially Aeschylus’ tragic play The Oresteia.

The Trojan War nicely illustrates the modern finding that a woman’s physical attractiveness predicts how intensely men work to retain their mate.Buss and Shackelford (1997).

It is not surprising, then, that humans have many feels directly related to attracting and keeping a mate.An excellent book-length treatment of jealousy, only a little dated at this point, is David Buss’ The Dangerous Passion: Why Jealousy Is as Necessary as Love and Sex. For early work on this topic, see Daly et al. (1982).

The stakes of sex and sexual relationships are so high that jealousy is a top cause of intimate partner violence, sometimes leading to murder.Buss and Duntley (2011).

In addition, in both men and women, the partner who sees themselves as getting a better deal in the relationship—with someone who is an especially good catch for them—tends to experience greater jealousy.Buss and Haselton (2005).

This explains much about male jealousy, not least, for example, why male interrogations regarding infidelity are often focused—sometimes obsessively—on the question of sex: Did you have sex with him?Kuhle et al. (2009).

Substantial research confirms that men experience greater jealousy in response to sexual infidelity than women do, a finding that replicates across cultures.Larsen et al. (2021).

For the same reason, women, when confronted with infidelity, are more likely than men are to deny that the relationship was sexual.Kuhle et al. (2009).

And, symmetrically to the female case, males are more likely to deny an emotional connection under interrogation.Kuhle et al. (2009).

While jealousy, with some justice, gets a bad rap, it’s worth noting that research suggests that a certain amount of jealousy can actually increase the chance a couple will stay together.See, for example, Sheets et al. (1997), for early suggestive evidence.

Tragically, much violence, including death, has resulted from such situations.Buss (2006).

Men are more likely to invest in their partner by giving gifts, paying more attention, and finally getting around to fixing the damn garage door.Sela et al. (2017).

Non-lethal violence can be used to deter both rivals and partners, signaling that infidelity will invite potentially greater attacks.Buss and Duntley (2011).

Feel 43: Jealous—Friendship

Indeed, people deny that their friendships amount to trading favors,Fiske and Tetlock (1997).

Indeed, people deny that their friendships amount to trading favors, and if you’re keeping track of favors, well, are you really friends?Clark (1984).

was getting from Japan in the 1980s—gainsDeScioli and Kurzban (2011).

That is, instead, human friendships are alliances.This idea was first advanced in Peter DeScioli’s doctoral dissertation, filed in 2008. See also DeScioli and Kurzban (2009b).

People compete for these valuable friendship slots.Krems et al. (2021).

In the modern world, another potential cause of friendship jealousy stems from technology: seeing a friend post to social media with someone else.Vaillancourt et al. (2024).

The closer the friendship, the more the jealousy.Krems et al. (2021). See Studies 3a and 3b.

Unlike the case of romantic jealousy, friendship jealousy is not as well researched and relatively little data, outside of children and adolescents,See, for example, Selman (1980), Parker et al. (2005), and Lavallee and Parker (2009). Not long ago, Krems et al. (2021) suggested that “empirical research [on friendship jealousy] has almost exclusively examined children and adolescents” (p. 980). Note that Parker et al. (2005) indicated that, at that point, “Virtually no empirical data exist on young adolescents’ jealousy over friends” (p. 235). My read of the literature is that it has not expanded greatly in the intervening 20 years.

For example, early work using interviews and focus groups revealed that teenage girls in Australian schools used false rumors with the purpose of dissolving others’ close friendships to make room for their own.Owens et al. (2000).

More recent research using experimental methods has shown that people feel more jealousy when they lose a friendship to another person as opposed to just losing the friendship, such as when a friend moves.Krems et al. (2021), Study 6.

These results neatly illustrate that jealousy is specific to the threat of being replaced in the friendship queue, not just losing one’s friend’s attention.Krems et al. (2021), Study 6.

Among young people, common strategies when someone is threatening a relationship are to ridicule the interloper and deploy smear tactics, especially divulging damaging secrets about the rival.Archer and Coyne (2005); Parker et al. (2005).

…friendship is threatened by a third party, people say that they will spend time and effort to gather evidence, attend to who the threat is, and determine just how close the relationship is becoming.Krems et al. (2021).

…including attestations of the strength of one’s feelings and “friend guarding,” using tactics such as persuading the friend who is at risk to stay away from places that the rival is likely to be.Krems et al. (2021).

Feel 44: Hatred

…Achilles’ close friend Patroclus, Achilles’ antipathy toward Hector was so intense that he told him he wanted to “cut your flesh into pieces and eat it raw, for the ill you have done me.”This is from The Iliad. Translations vary, but this one is from Samuel Butler’s 1898 rendering.

Hate is designed to deal with such people.This chapter draws heavily on Sell et al. (2024), which is, to my mind, the best functional account of hate to date. See Landers et al. (2025) for a recent extension with empirical work.

Because it is important to take steps to neutralizeI draw this notion of “neutralizing” from Sell et al. (2024). As they put it, their results show the following (my italics): “Anger produces behaviors functionally designed to bargain for better treatment through recalibration, while hatred produces behaviors functionally designed to neutralize targets costly to the hater.”

…believe that someone feels they have reason to harm you—even if the reason is that you did unto them first—then the hate system takes this measurement and gets to work hating them in return.Schopler and Compere (1971).

Many people have experienced a hatred so intense that they might well have contemplated such a thing.See Buss (2006), The Murderer Next Door, for some surprising data regarding how common homicidal fantasies are.

When people nurture hate, they fixate on the hated individualAumer and Bahn (2016).

Given that gossip and character assassination rarely allow for the victim to respond, great gains can be had against a target provided there is no one to counter the negative information.”Sell et al. (2024).

When it comes to hate, this is especially the case: Bearing hate means enjoying when the hated individual suffers, even if one wasn’t the cause.Rempel et al. (2019).

Related, signs that the person is fully submissive and ready to surrender might increase rather than decrease aggression from haters.Sell et al. (2024).

Feel 45: Contempt

Each part of our social lives, like a character’s inventory, has a capacity.See especially the work of Robin Dunbar. See, for example, Dunbar (1992).

Contempt is, then, less about a specific action someone took and more about how those actions give insight into a person’s character.Fischer and Giner-Sorolla (2016).

ResearchClassic work on this includes Rozin et al. (1999), Hutcherson and Gross (2011), and Caprariello et al. (2009).

…steals a purse from a blind person,” “a 16-year old refuses to give up his/her seat on the bus to a crippled old lady,” or “a man comes home drunk and beats his wife.”Fischer and Roseman (2007).

Contempt motivates avoidance and, especially, the severing of relationships.Schriber et al. (2017) refer to “avoidant/dismissive action tendencies.” Scholars who do not come from an evolutionary perspective have argued that the “function” of contempt is to uphold and enforce cultural norms, exclude others, and harm the target’s status. See, for example, Morris and Keltner (2000). Note that these aren’t “functions” in the way that the evolutionary analysis defines the term.

Such treatment might be in the form of sharp criticism, a consistent refrain of “whatever,” or the well-known one-sided smirk and eye-roll treatment.Melwani and Barsade (2011).

For instance, some research indicates that someone who expresses contempt is seen as higher in status by their peers.Keltner et al. (1998).

Contempt has reliably been found to be among the best if not the best predictorGottman (1993).

Contempt has reliably been found to be among the best if not the best predictor of divorce.Gottman (2014).

People are less likely to form relationships with—whether personal, in the workplace, or romantic relationships—those for whom they feel contempt.Melwani and Barsade (2011).

Feel 46: Resentment

When the gods gathered for the wedding of Peleus and Thetis—the pair would go on to produce the great Achilles—one divine name was conspicuously absent from the guest list: Eris, goddess of discord.As with so many Greek myths, accounts by different sources vary. I chose the account that illustrates the emotion I’m discussing here.

For example, nearly every human society that has been studied has a prohibition against murder, though the details vary.Mikhail (2009).

…exquisitely good at noticing when there has been a violation: Someone enjoyed a benefit but did not pay the cost or someone did not get a benefit for which they did pay the cost.This point about meeting the requirement is important, but it’s unwieldy to repeat it every time, so for the rest of this chapter I will just refer to costs, as a shorthand. The argument relies on the notion of meeting the requirement, but I don’t repeat it.

They termed this ability “cheater detection” and have provided decades of evidence that we humans are experts in it.See Cosmides (1989) and Cosmides and Tooby (1992) as well as subsequent work on cheater detection and social exchange, including Cosmides and Tooby (2005) and Cosmides et al. (2005).

In the third case, Eris clearly met the requirement—she was a goddess and therefore entitled to attend—but did not get the benefit of the invite.Gigerenzer and Hug (1992).

As something of a side note, it’s tempting to link resentment and “fairness,” but I’ve tried to avoid using this word because it can mean many different things to different people in different contexts.DeScioli et al. (2014).

If someone gets less than they want for nearly any reason, they’ll often say it’s unfair.Johnson-Saylor (1986) reports that in interviews, subjects discussing resentment frequently use terms such as “unfairness” or “felt deprivation” (p. 57). She finds that resentment is often associated with feelings of helplessness. In a careful discussion of the distinction between resentment and anger, Weber (2015) concludes that the “best way…is to characterize anger in terms of harmful or threatening events, and resentment in terms of violations of group interpersonal norms” (p. 44).

…don’t doubt that Hera, Aphrodite, and Athena all argued that the apple should, in fairness, go to them, but it is equally clear that it was vanity more than fairness that was at work.As usual, there is limited text to go on. I imagine this is how they would have argued.

Early research on resentment found that in some situations, people who felt resentment, especially the powerless, suppressed their responses.Johnson-Saylor (1986). She reviews research (p. 50) that “reveals a consistent theme of inhibited expression of an angry emotional response.” She suggests that this inhibition is a definitional feature of resentment.

…however, suggests that the feeling of resentment often leads to criticism and derogatory statements, not always directed at the person who got the benefits but often to the resented person’s family, friends, and allies.Feather and Nairn (2005), for example, cite work suggesting that “feelings of resentment proper contrast with hostile envy because they are less private and have more of a public, sanctioned character” (p. 88), my italics.

After all, in many cultures, complaining about slights and injustices is often viewed negatively: One can come across as whiny or small-minded.Johnson-Saylor (1986).

In sum, resentment motivates aggression, often in the form of denigrationFeather and Nairn (2005).

By recruiting others to the cause, it might be possible to right the wrong, harm the rival, and deter future instances.This idea has deep roots. Adam Smith, in The Theory of Moral Sentiments, wrote that resentment is “given us by nature for defence, and defence only” (p. 79, Smith’s (British) spelling).

Feel 47: Proud

People who celebrate accomplishments around the world assume big postures—as do victorious chimpanzees—making themselves maximally visible.Tracy and Matsumoto (2008).

That’s a strong criticism, except for one thing: Tracy and Matsumoto also looked at athletes who were blind from birth, precluding the possibility that these winners were imitating what they had previously seen.See Tracy and Matsumoto (2008). See Figure 3 for images of two of the blind victors. See also Cowen et al. (2021) for recent work showing the universality of the facial expression that accompanies this feeling.

In short, we seek status.Sznycer and Cohen (2021).

The feeling of pride is a crucial part of the quest for status because it helps track how well we’re doing.For a recent review, see Tracy et al. (2023). They and others note that pride is a “self-conscious emotion,” based on feelings that are about oneself rather than others. While this distinction looms large in some general accounts of emotions, I ignore this distinction in favor of the classification scheme animating this book.

Pride measures status gains, increases in how much others value you.Tracy et al. (2020), p. 53. Elsewhere, they use a similar metaphor, writing that “that pride functions in part as an internal barometer of success…” (p. 83, my emphasis).

It’s the pride you get when you dominate others through power, often physical coercion, leading to a certain kind of respect.Sznycer et al. (2017).

For a social species, with so many others around to help or hinder, being valued and being respected are two precious commodities to cultivate.In the literature on pride, as in many topics, there are distinguishable schools of thought that have interesting and important connections to one another. My view is that scholars such as Jessica Tracy, drawing on the anthropological flavor of evolutionary approaches, lean on the prestige/dominance distinction in the literature on status in a way that mirrors the distinction by scholars such as Daniel Sznycer, in the evolutionary psychology community, which draws the distinction between adaptations to invite benefits versus adaptations to deter harm. Prestige invites benefits and dominance deters harm. To my eye, nothing much turns on which flavor of this distinction one prefers. See, for instance, Dickens and Robins (2022) for recent work.

…for becoming a valued group member who abides by social norms and is successful at his or her most important pursuits: self-regulation, hard work and persistence, cooperation, and an orientation toward fairness and generosity.”Tracy et al. (2020), p. 69. A similar view is that of Cheng et al. (2010), who argue that “pride evolved as a mechanism for motivating behaviors oriented toward increasing social status and informing other group members of self-perceived status shifts” (p. 335).

People choose the sorts of pursuits that they judge within their ability that will lead to the greatest increase in status in the eyes of their audience.For an excellent discussion and intriguing data, see Sznycer and Cohen (2021).

Unlike many of the social feels, pride feels good, not bad.Mauro et al. (1992).

Indeed, unlike most feels, experiencing pride makes one feel good about oneself, as opposed to about something that happened or about someone else.Tracy et al. (2023).

It’s not just accomplishment: Feeling pride about being generous motivates additional generosity.For coverage of both findings, see Tracy et al. (2020). See Williams and DeSteno (2008) and see Tracy et al. (2023) for a review of similar findings.

Feel 48: Amused

He who laughs last probably didn’t get the joke.Attributions vary. Possibly Carroll Bryant. Maybe Charles de Gaulle.

The sense of finding something funny is one of the toughest feels to understand.It’s nearly 20 years ago now, but, still, Flamson and Barrett (2008) asserted that “formal explanations of humor remain in their infancy.” As of this writing, the field has grown up a little but probably not past being a toddler—or at best a young child. See Hurley et al. (2013).

Haw haw haw…Early research on humor and laughing showed that people laugh and smile at humor more when they think they are being observed than when they are alone.Fridlund (1991).

The social element adds another.Flamson and Barrett (2008), p. 265.

Smarter people are better at creating humor, and this ability predicts success on the mating market, including, for men, how many sexual partners one has over the course of a lifetime.Greengross and Miller (2011).

Feel 49: A Sense of Belonging

A significant number of other males are excluded from mating—more than 70%, in one study—yet the bachelor males don’t form gangs to depose the alpha.Le Boeuf (1974), in classic work on northern elephant seals, estimated that “less than one-third of the males in a residence during a season copulate” (p. 165). The same extreme polygyny occurs in southern elephant seals (Fabiani et al., 2004).

Why don’t slightly smaller males stage a coup?Le Boeuf (1974) notes that fights are one on one, writing: “Each bull keeps male lower in rank than himself from approaching” (p. 164).

If #3 joins #2, after the fight, #2 might well turn on his former ally.Tooby and Cosmides (2010) provide an excellent discussion of barriers to cooperation.

While some non-human animals build impressive homes and even do a little agriculture,Mehdiabadi and Schultz (2010).

In group-living species, being a loner is dangerous.See Connor and Krützen (2015) for an excellent discussion of the data on dolphin alliances. See Wrangham’s work on chimpanzees, for example, Wrangham and Glowacki (2012), which reviews evidence of chimpanzee violence. Importantly, they write. “Lethal attacks have been reported only where there is a strong asymmetry of power between subgroups, typically when several males encounter either a lone male from the neighboring community or a lone mother with her dependent offspring” (p. 9).

We have, as social psychologists have put it, a fundamental need to belong.Baumeister and Leary (1995) is a classic. See Baumeister and Leary (2017) for a more recent statement of their views.

…very much ahead of his time, psychologist Mark Leary in the 1990s coined the term sociometer, a psychological system designed to keep track of how one was doing when it comes to other people.Leary (2012) writes, “The idea for sociometer theory emerged amidst the questions and controversies that swirled around the construct of self-esteem in the early 1990s. Spurred partly by my reading in the emerging field of evolutionary psychology, I began to wonder about the adaptive significance of self-esteem.”

This idea—inspired in part by his reading in evolutionary psychologyLeary (2012), p. 143.

This idea—inspired in part by his reading in evolutionary psychology—was developed with collaborators in the following yearsThe classic paper is Baumeister and Leary (1995).

According to Leary, the sociometer is “a subjective gauge of the degree to which [someone is] relationally valued and socially accepted by other people.”Leary (2012), p. 145. The notion of “relational value” was added after the first conceptualization. See Leary (2001).

Since the idea was developed, a tremendous amount of evidence has accumulated that being included feels good and being excluded feels bad.Leary (2012) reviews evidence to that point.

In laboratory studies, when participants are told that some subjects chose others to work with, people do indeed feel bad.For a meta-analysis up to that point, see Blackhart et al. (2009).

…came into the lab and played Cyberball, typically a three-player game in which, over time, the participant watches as the other two in the game throw the ball to each other, excluding the subject.Williams et al. (2000).

This leads to hurt feelings, activating the same parts of the brain associated with physical pain.Mwilambwe-Tshilobo and Spreng (2020).

These benefits extend into later years, as greater belonging has been found to be correlated with job success.Support for the claims in this paragraph can be found in Allen et al. (2022) and the citations therein, p. 1135.

Being socially connected is one of the most important predictors of overall happiness and success.See Leary (2012), p. 143.

In some groups, becoming a member requires harming members of other groups, a strong signal of one’s dedication and commitment.I have in mind certain gang initiation rituals here, but history is replete with examples.

Referring to some of the beliefs of the supposed intellectual elite, George Orwell wrote, “One has to belong to the intelligentsia to believe things like that: no ordinary man could be such a fool.”Orwell wrote this in an essay in 1945 entitled, “Notes on Nationalism.” Bertrand Russell made a similar remark in “My Philosophical Development,” writing, “This is one of those views which are so absurd that only very learned men could possibly adopt them.”

…that you differentially support it, compared to rival groups…The more biased away from neutral truth, the better the communication functions to affirm coalitional identity, generating polarization in excess of actual policy disagreements.”This quote is from Tooby’s essay for Edge entitled “Coalitional Instincts” (2017) and can be found at the following link: https://www.edge.org/conversation/john_tooby-coalitional-instincts.

Feel 50: Lonely

Evidence from the non-human animal literature shows that among social species, expulsion from a group significantly increases the risk of death.Lancaster (1986). She writes that in primate societies, ostracism “carries high risk and is associated with increased mortality and morbidity” (p. 223).

In the laboratory, when experimenters contrive to make subjects feel lonely, those subjects report anxiety and fear.Cacioppo, Hawkley, et al. (2006).

Loneliness measures the extent to which one lacks friends and allies, and the feeling motivates doing something about it.Cacioppo et al. (2014).

Among some groups of people, upwards of 80% report being lonely at least some of the time.Hawkley and Cacioppo (2010). For more recent data, see Bruss et al. (2024). They summarize their findings this way: “Loneliness and lack of social connection are widespread and pose a threat to mental and physical health.” Generally, while estimates of loneliness vary, there seems to be agreement that it is on the rise in the U.S. and other countries. For a nice treatment, see Derek Thompson’s piece “The Anti-Social Century” in The Atlantic, January 8, 2025.

And there is evidence that this problem is getting worse, exacerbated by changing technologies and, not so long ago, the ravages of a global pandemic.But it was happening before the pandemic. See Bowling Alone by Robert Putnam, which was published in 2000.

And given the dangers of social isolation, it’s no wonder that loneliness can be especially painful.Jaremka et al. (2013).

Loneliness leads not only to sadness but also to depression.Cacioppo et al. (2014).

While the number of people in one’s network matters, loneliness is better predicted by the quality of one’s connections.Cacioppo et al. (2014).

Finally, am I a member of groups and associations, a factor especially important for men.Hawkley et al. (2005). They refer to the three dimensions as Isolation, Relational Connectedness, and Collective Connectedness. Coalitions and alliances are likely to have been more important for males than females over evolutionary time. See Kurzban et al. (2001) for my view. The book Men in Groups is an excellent and classic work on this topic.

Indeed, loneliness has a tremendous impact on health, including increased blood pressure, less sleep, and cardiovascular disease.Masi et al. (2011).

Loneliness is even a significant risk factor for early mortality.Holt-Lunstad et al. (2015); Rico-Uribe et al. (2018).

…leading researchers of loneliness John Cacioppo and colleagues put it this way: “The social pain of loneliness and the social reward of connecting with others motivate the person to repair and maintain social connections.”Cacioppo, Hawkley, et al. (2006), p. 1056.

Research has shown, perhaps unsurprisingly, that lonely people find their social interactions less positive.Cacioppo et al. (2014).

…that lonely people seem to be increasingly attuned to danger: They pay more attention to words having to do with social threats and are more sensitive to the expression of pain on people’s faces.Cacioppo et al. (2014).

Lonely people expect that social interactions will not go well and take fewer social risks.Gere and MacDonald (2010).

The lonely also remember more negative social information than those who aren’t lonely.Hawkley and Cacioppo (2010).

Puzzlingly, some evidence suggests that lonely people behave in ways that would seem to undermine their social connections.Gere and MacDonald (2010), for instance, write, “Perhaps the most straightforward prediction of behavior following threats to belongingness is that excluded individuals should want to seek reparative sources of connection. The data, however, are not nearly as straightforward as the prediction.”

…were given a choice about which snacks to give the players who excluded them, and they chose the less desirable ones—prunes rather than cookies—in what seems to be a somewhat petty act of revenge.Chow et al. (2008).

For example, lonely people will work harder when doing so will help them to earn a place in the group.See Gere and MacDonald (2010) for a review of the literature to that point.

…to “express greater interest in making new friends, to increase their desire to work with others, to form more positive impressions of novel social targets, and to assign greater rewards to new interaction partners.”Maner et al. (2007).

This accords with a great deal of other evidence that loneliness can, under the right conditions, successfully motivate making new and better social connections, which in turn reduces the unpleasant feeling of loneliness.Hawkley and Cacioppo (2010), p. 218.

Feel 51: Judgy—The Moral Sense

He had, however, broken a taboo.Jon Haidt has examples of stories in which no harm is done but people judge the action wrong. I chose this example to avoid examples that are either well worn, as in the case of consensual incest, or a bit disgusting, such as having sex with a dead chicken. See his book The Righteous Mind (2012) for additional details.

I’m not talking about virtue, conscience, or cooperation, three ideas that scholars often blur with the notion of “morality.”See, for instance, Curry et al. (2019) and James Q. Wilson’s book, The Moral Sense.

This feel has to do with your perception of others’ wrongful actions.The ideas in this chapter are developed in my scholarly work. See especially DeScioli and Kurzban (2009a) and DeScioli and Kurzban (2013). Note that my views on morality and the moral sense are not widely accepted by the scholarly community. Therefore, this feel is more of a personal view as opposed to reflecting the scientific consensus.

The reason we have this feeling is the topic of ongoing debate,See DeScioli and Kurzban (2013).

I myself have a dog in this fight, so in this chapter, I’m just going to back my own pooch.See the work of Jon Haidt, Kurt Gray, Oliver Curry, Daniel Sznycer, and James Q. Wilson. There are of course many more scholars working in this literature, too many to name and cite.

(Siding with the most powerful, for example, makes a lot of sense when the gods are involved.) People can also try to stay neutral, but neutrality may be costly, impractical, or impossible.Shaw et al. (2017).

In sum, the evolved function of moral judgment is to put you on the same side as others when conflicts emerge.I’ve obviously simplified here. See DeScioli and Kurzban (2013) for a more thorough treatment.

As he put it, “Descriptive fieldwork on a worldwide scale…demonstrated that moral judgments are ubiquitous in human groups.”Shweder (2012), p. 89.

…demonstrated that moral judgments are ubiquitous in human groups.” He added that “moral judgments (that’s good, that’s wrong, that’s sinful) around the world are also felt,” likening these feelings to “aesthetic and emotional reactions.”Shweder (2012), p. 89.

All cultures have rules about intentionally harming others, such as killing and assault.See, for instance, Mikhail (2009); Robinson and Kurzban (2006).

…we perceive behavior, we feel the sense of wrongness when the behavior is prohibited by one of these rules, even if we can’t always articulate what the rule is or why it was made.See Steve Pinker’s The Language Instinct for an excellent treatment of the same phenomenon when it comes to identifying grammatical errors. Jon Haidt’s work on moral dumbfounding is the classic source for the claim in the moral domain.

The moral sense is emphatically not simply measuring intended harm.See the work of Kurt Gray, for example, Gray et al. (2012).

…moral anthropology as an empirical undertaking is in some significant measure the history of the discovery of astonishing cultural variations in human judgments about the proper moral charter for an ideal way of life.See Shweder (2012), p. 90.

The prohibition against murder is universal.Mikhail (2009). See also Sznycer et al. (2023).

Early work by George Peter Murdock in his broad review of cultures concluded that “incest taboos apply universally to all persons of the opposite sex within the nuclear family.”Murdock (1949). Wolf (2014). Lieberman and Patrick (2022).

…nuclear family.” Psychologist Deb Lieberman has more recently added to the evidence that the aversion to incest and the disgust that accompanies considering it are widespread, as we saw in the chapter on disgust.Lieberman and Patrick (2022); Lieberman et al. (2003).

If we ask Aldous Huxley,Huxley wrote this in an introduction that he wrote for an edition of Samuel Butler’s novel, Erewhon, according to the online site Quote Investigator.

This allows everyone to gang up on the (alleged) violator of the moral rule.See Steve Pinker’s (2025) recent book What Everyone Knows That Everyone Knows for more on the power of shared knowledge.

In New England during the 17th century, the Puritans meted out harsh punishments, including death, for holding sinful beliefs.Fitouchi et al. (2023).

In parts of the world today, people are punished for their choice of clothing, such as Iranian women who refused to wear a hijab.I have in mind failure to wear a hijab, in Iran.

These days, moralistic mobs on the internet mete out vigilante punishments for minor transgressions—even accidental ones, destroying livelihood and lives.This material is from a post on Living Fossils, entitled Hiking Tales and the Function of Morality, available at the following: https://thelivingfossils.substack.com/p/hiking-tales-and-the-function-of. See also DeScioli and Kurzban (2009a, 2018).

The reverse is true as well, and some grave offenses get off with too little punishment.The debate that was raging at the time of this writing in England about grooming gangs similarly illustrates how small penalties are sometimes imposed for large wrongs. See also Robinson and Kurzban (2006) and work by Daniel Sznycer for more on this topic.

Feeling judgy should, therefore, be understood for what it is at its heart: a call to attack.DeScioli (2025). This paper, entitled The Moral Sword, lays out the arguments in this chapter in detail.

Feel 52: Admiration

Samuel Smiles, in 1871, said that “admiration of great men, living or dead, naturally evokes imitation of them in a greater or less degree.”This quotation is from chapter 2 in his book Character. I verified this here: https://www.gutenberg.org/files/2541/2541-h/2541-h.htm.

While, like many of the feels, admiration has received surprisingly little scholarly attention,Onu et al. (2016) wrote that “admiration is surprisingly little theorized or studied empirically” (p. 218). Indeed, other than their review and the attention Henrich and Gil-White (2001) paid to the emotion in the context of their work on status, this does seem to be the case.

There is evidence that admiration is focused on accomplishments, excellence, and signs of success.Immordino-Yang et al. (2009). See Onu et al. (2016) for a review.

The emotion is, as psychologists have called it, one of upward comparison: We feel admiration for those who demonstrate more competence in the relevant domain than we have.Van de Ven et al. (2011).

…you lack the skills or resources—or you simply aren’t interested in acquiring their skillset, then again, there’s not much point to trying to emulate them, and admiration can turn to envy or just indifference.Van de Ven and Zeelenberg (2015). See the citations in the envy chapter for additional sources.

…the case of envy, is important: We are more likely to feel admiration of the accomplishments of the target if we ourselves might plausibly reach or exceed the skills of the person we admire.Smith (2000).

While we may fear the dominant, we admire the prestigious.Henrich and Gil-White (2001). Fessler and Haley (2003).

The motivation tied to admiration has two components.Onu et al. (2016) (citations omitted) write, “Admiration for others encourages people to learn valuable skills and praise those of extraordinary talent.”

We seek proximity to the accomplished and to work to be like them.Onu et al. (2016), pp. 224–225.

Admiration even affects memory: We remember those we admire more than others.Onu et al. (2015).

Laboratory research shows that people say they intend to praise the people they admire, bolstering their reputation.Algoe and Haidt (2009).

Feel 53: Embarrassed

Mark Twain is frequently quoted as saying that “Man is the only animal that blushes…or needs to.”This appears in Following the Equator (1897), ‘Pudd’nhead Wilson’s New Calendar,’ ch. 27.

Embarrassment is another one of the trickier feels and has gotten less scholarly attention than the popular ones, such as anger and fear.Early views of embarrassment held that the emotion was due to “a negative social evaluation” or “the disruption of a social performance” (Sabini et al., 2000). These scholars divided embarrassment into three types, which they labelled faux pas, center of attention, and sticky situations, the last of which were cases such as asking a friend to repay a loan.

When people feel embarrassed, there is a characteristic set of facial expressions and body movements—averted gaze, a sort of suppressed smileKeltner and Anderson (2000).

As a general matter, people view you much more negatively if you break a rule intentionally as opposed to accidentally.See Mayer et al. (2021), Section 3. Discussing embarrassment: “Accidental mishaps do not necessarily reflect the personal character or flawed aspects of the self, as the behavior may well be caused by peculiarities of the specific situation. In contrast, assuming that an actor has intentionally violated a social norm allows observers to draw conclusions about the nature of the target’s character, since the target has control over their actions and can be held responsible accordingly.”

This performance is the person’s way of saying, Oops, this was an accident and I am quickly taking remedial action.Keltner and Anderson (2000).

Other species do signal a kind of deference, often referred to as appeasement.Keltner and Buswell (1997).

Research confirms that it works: People who show embarrassment, including children, are treated better after a transgression than those who don’t.Keltner and Anderson (2000).

How many people have avoided medical care because they wanted to avoid the embarrassment of discussing the possibility of having, say, a sexually transmitted infection?Harris (2006).

Second, embarrassment motivates adding additional explanation for whatever occurred,Harris (2006), p. 528.

Second, embarrassment motivates adding additional explanation for whatever occurred, whether using our words or our exaggerated movements.Harris (2006).

There is an interesting link between violating norms or conventions and humor,See Mayer et al. (2021), for an interesting discussion and analysis.

Feel 54: Shame

This infamous scene from Game of Thrones offers a visceral depiction of the emotion,This scene appears in the tenth and final episode of season 5, entitled Mother’s Mercy. The scene is rendered somewhat differently from the way it appears in the book, A Dance with Dragons by George R.R. Martin.

This infamous scene from Game of Thrones offers a visceral depiction of the emotion, a public unveiling of personal failure that serves as both punishment and deterrent.Schaumberg and Skowronek (2022).

Work by anthropologists suggests that shame is found in every society in which it has been investigated.Sznycer et al. (2016).

Shame comes in early in development—even young children experience itLewis et al. (1992).

…development—even young children experience it—and, just as we saw in the chapter on pride, the distinctive posture of the emotion—a quiet, slumped body with eyes downcast—appears even among those who are blind from birth.Tracy and Matsumoto (2008).

Shame is similar, designed for damage control in the world of information warfare.Landers et al. (2024). Sznycer et al. (2021).

In particular, the feel is a defense against an informational attack that reduces how valuable people think you are.Sznycer et al. (2016).

Other attacks are possible as well, including claims that one lacks skills, has behaved selfishly (if not necessarily immorally), is burdened by a communicable disease, has been victimized, and so on.Kurzban and Leary (2001).

To solve the adaptive problem of devaluation, shame measures the size of the attack.Leroux et al. (2023).

You might think that people feel shame to the extent to which what they did was, in their view, actually shameful, falling short of community standards in some way.Tangney et al. (2007). See especially Sznycer et al. (2016).

When subjects imagine themselves in that awkward predicament, they report that they would feel shame, despite their innocence.Robertson et al. (2018), Study 1.

People who were excluded reported feeling shame at being excluded, even when they had been generous in the previous task.Robertson et al. (2018), Study 2. The authors conclude, “In Study 2, exclusion, ostensibly for uncooperativeness in a public good game, elicited shame independently of participants’ actual contribution level” (p. 571).

However, the sad fact is that in some cultures, having been sexually assaulted is seen as reducing someone’s value.To take but one recent example, Olamijuwon and Odimegwu (2022) suggest that in some cultures, “Virginity is symbolic of pride, dignity, and respect” (p. 569).

The same pattern holds in many other cases in which one is the victim rather than the offender.See Landers and Sznycer (2022) for a discussion and additional citations.

We share this pattern with our non-human animal relatives: Subordinates signal submission with similar postures.Fessler (1999).

Mencken referred to conscience as “the inner voice that warns us somebody may be looking,”Mencken (2011).

The desire to avoid shame acts not just after the fact, but before.Leary (2015).

Finally, sometimes the best defense is a good offense: Shame has been shown to motivate aggression, which can take many forms, including physical violence.See Elison et al. (2014) for a thorough review of the literature on the relationship between shame and aggression to that point.

This can include building one’s social value in other ways, cultivating new relationships and alliances, and taking action to prevent a recurrence.Forster et al. (2021).

Apologies can signal that one accepts the lower value, potentially mitigating subsequent attacks.See Landers and Sznycer (2022) for a discussion. More generally, on apologies, see work by Michael McCullough and colleagues, for example, McCauley et al. (2022).

Generally, shame motivates an array of behaviors—generosity, hostility, hiding, apologizing, self-improvement, and so on—because there are many different kinds of defenses against being devalued.Landers and Sznycer (2022), in their section entitled “The information threat theory can account for many known features of shame.” I retain the British spellings, and I omit the citations.

Feel 55: Guilt

One team of researchers,Landers et al. (2024).

In contrast, and consistent with the view I’ve suggested here, when they hit the likable intern’s car, they felt guilt but not shame.See Figure 1 of Landers et al. (2024) for the formal path analysis of these relationships as operationalized in this study.

What is the explanation for this motive to confess?See Sznycer et al. (2015) for a more thorough discussion.

A confession might, if the confessor’s contrition is believed, reduce the victim’s desire for revenge.Sznycer et al. (2015).

Indeed, in courtrooms, confession and expression of genuine remorse do often reduce the sentence.Proeve (2023).

Confession avoids this possibility, reducing the total harm that might come from the offense.See Sznycer et al. (2015) for relevant data.

Why do we have moods?Nettle and Bateson (2012) provide a nice overview of these ideas. Note that I could have included anxious as a mood, but I discussed anxiety in the second Kingdom.

Feel 56: Sad

Persephone had been gathering flowers in a sunlit meadow one day when Hades, master of the underworld, emerged from a massive split in the earth and abducted her to his domain.This is Homer’s account. Ovid’s version leaves the matter a bit more ambiguous. The recent Netflix series Kaos seems closer to Ovid’s account.

Eventually, however, she ate six pomegranate seeds,Again, sources vary on the number of seeds.

As we can see with the case of Demeter, as Henry Wadsworth Longfellow put it, “Into each life some rain must fall.”Longfellow (1872). The line appears in the poem, “The Rainy Day.”

We feel sadness when we experience losses, including the death or, in Demeter’s case, abduction of a beloved family member.Tooby and Cosmides (1990). See Scherer and Wallbott (1994) for an extensive look at emotional responses across cultures.

The sadness we feel tends to be roughly in proportion to the setback or loss.Nesse (2000b). Nezlek and Plesko (2003). They find, perhaps not surprisingly that “daily psychological well-being…was higher on days when more positive events occurred and was lower on days when more negative events occurred” (p. 593). People are sadder when bad things happen to them.

…a child, the sadness they feel is always great, but it is greater when the lost child was closer to the age of reproduction, reflecting the loss of someone closer to achieving reproductive success.Crawford et al. (1989).

While researchers have suggested that the two kinds of sadness—personal losses and failing to reach goalsHagen and Barrett (2007).

While researchers have suggested that the two kinds of sadness—personal losses and failing to reach goals—have slightly different psychological and physiological profiles,Shirai and Suzuki (2017).

Sad people move more slowly, slouch, and withdraw from the social world.See, for example, Huron (2018).

Under these conditions of uncertainty, people did, in fact, give more money to the player who displayed a sad expression compared to a neutral expression.Reed and DeScioli (2017).

So, just as we saw in the cases of grief and depression, credibly signaling your losses can be used to secure help.Not all agree. Huron (2018) argues that the constellation of features of sadness are a cue rather than a signal. That is, the features are not designed to convey information, even if others can use the features to draw inferences.

The second motivation is suggested by the fact that sad people are less sociable than happy people.See, for example, Leventhal (2008) for a discussion.

Darwin noticed that sadness makes people “languid.”Huron (2018) pointed this out. The word appears in Darwin’s The Expression of the Emotions in Man and Animals.

As one scholar recently put it, sadness makes us retreat into reflection: “The most important behavioral change, however, is cognitive: sadness tends to lead to sustained reflection about one’s life situation.”This quote is on p. 60 of Huron (2018), citing Nesse (1991), and Andrews and Thomson (2009).

Sad people speak less and talk more softly when they do.Huron (2018).

One theory, in parallel to what we saw in the discussion of grief, is that when people have suffered a significant loss, they need to rethink their beliefs, behaviors, and plans.Tooby et al. (2008). See Huron (2018), who suggests that sad people reflect as opposed to ruminate.

People who write about their feelings subsequently show less anxiety, better performance at work or school, and even better health as measured by the number of doctor’s visits.Gortner et al. (2006); Graf et al. (2008); Smyth (1998).

In sum, sadness motivates signaling a need to get support and taking the time to plan for the future to address whatever it is that is making us sad.Huron (2018).

People who endure horrible loss—the death of a loved one or a debilitating injury—report, after some time, being more happy than sad.For classic work on this, see Brickman et al. (1978).

Sadness to do with failing to reach a goal fades faster than the loss of a family member,Shirai and Suzuki (2017).

Sadness to do with failing to reach a goal fades faster than the loss of a family member, though this decline happens even for those who suffer extreme loss.Lucas et al. (2003).

The negative quality of this feeling is designed to discourage us from repeating whatever resulted in the loss or failure.For more on sadness, see Good Reasons for Bad Feelings, by Randy Nesse.

Feel 57: Happy

Entire careers have been built around happiness,For example, see books by Martin Seligman (Authentic Happiness, 2002; Flourish, 2011), Sonja Lyubomirsky (The How of Happiness, 2008), and Paul Zak (Immersion, 2022).

Happiness is chronic.See, for example, Diener et al. (2015).

…idea to happiness and proposed that happiness is an assessment of how one is doing across a number of different domains relevant for survival and reproduction, reflecting answers to questions such as the following:The approach I take here follows the framework suggested by Lee Kirkpatrick and Bruce Ellis (2001), which itself follows Mark Leary’s sociometer model.

…idea to happiness and proposed that happiness is an assessment of how one is doing across a number of different domains relevant for survival and reproduction, reflecting answers to questions such as the following:I have tried to stay away from naming scholars in this work, but I mention these two in part because I feel as if this work is excellent and under-appreciated and, to be candid, Lee is a close friend of mine.

Am I healthy?See Diener et al. (2018) for a relatively recent overview. See Kenrick et al. (2010) for an evolutionary take related to happiness, building on the so-called hierarchy of needs.

The way that these and no doubt yet more measurements interact to determine how happy one feels is complicated.See Diener et al. (2015).

So, on the one hand, as one scholar put it, happiness is “a generic, undifferentiated response to pleasant circumstances.”Ellsworth and Smith (1988b), p. 326, quoting Weiner (1985).

On the other hand, to be very happy, at least some stuff has to be going right, but just one low measurement can matter a great deal.This view contrasts with others’ views. My former colleague at Penn, Marty Seligman, suggested in Authentic Happiness that happiness is a sum: a personal set point plus one’s circumstances in life plus what he calls “voluntary actions.” Generally, I like the fact that he sees the feeling as a measurement of some kind, which resonates with my view. However, there are not units provided for any of these, so it’s hard (for me, anyway) to think about how to evaluate this claim mathematically.

Even people who are struggling to meet their basic needs report being happy, possibly because they know of others who are even worse off.See Diener et al. (2015) for a brief discussion. They report that a majority of people experiencing hunger nonetheless say they are happy.

Now, it’s true that some surveys show that income matters, no doubt in large part because earning money in the modern world is necessary for meeting physical and social needs.Diener et al. (2015).

But the relationship between income and happiness remains a matter of debate.Kaliterna‑Lipovčan and Prizmić‑Larsen (2016) remarked that “the association between income and happiness is still a matter of scientific debate” (p. 1). See also Easterlin (1974) and Frank (1985).

Unsurprisingly, more money does help, but it helps more in some places than others, and in some countries, more money helps less than you might think, at least after a certain point.Diener et al. (2018). This research area is dynamic, and opinions differ on interpreting the available data.

We get used to our life circumstances as they improve, but our happiness returns more or less to baseline after big gains, such as winning the lottery, or losses, such as a disabling injury.Sadly, sadness from unpleasant life events lasts longer. See Diener et al. (2018).

…effect is seen even in the context of direct reproductive success: Getting married and having children does lead people to report being happy, but newlyweds and new parents return to baseline happiness relatively quickly.Lucas et al. (2003). Note that these researchers found that there are significant individual differences in the rate of adaptation.

In some classic work,Wirtz et al. (2003). The distinction between the experiencing and remembering self is from Kahneman (2011).

Finally, there are large individual differences in terms of baseline happiness.Here and elsewhere I omit detailed discussion of individual differences and their genetic origins. Generally, happiness shows strong heritability, in line with many other traits. Indeed, some researchers have suggested that most variation is due to differences in genes rather than life circumstances. See, for example, Lykken and Tellegen (1996), a widely cited foundational source for this claim. Diener et al. (2018) put the estimate of heritability, based on meta-analyses, in the 0.32 to 0.41 range.

…“subjective well-being,” depended on, first, how well one was able to fulfill one’s basic physical needs, such as having food and shelter, and, second, social variables, such as feeling respected and supported by others.Tay and Diener (2011).

Other work has shown that better health, more education, and greater satisfaction with one’s job all predict overall happiness.Diener et al. (2015).

So if happiness, broadly, is designed to measure overall how we’re doing in solving important adaptive problems,Grinde (2012), for example, suggests that happiness should be defined this way, writing (p. 52), “It seems pertinent to define happiness as the sum of activity, or net output, of the mood modules.” Note the commitment to a sum, in line with Seligman’s notion.

Indeed, there is abundant evidence that greater happiness creates good outcomes across an array of domains, including health, longevity, social relationships, and cognitive areas such as planning and creativity.See Diener et al. (2015) for a thorough evaluation and review of the causal claims regarding the effect of happiness. See Fredrickson’s work on her “broaden and build” model. See, for instance, Fredrickson (1998). See especially Figure 1.

Happier people seem to work to grow their assets, especially in the social world: Research suggests happier people are kinder and pro-social.Otake et al. (2006). See also Mehl et al. (2010).

People who found this little treasure were more likely to help someone who dropped papers than those who did not.Isen and Simmonds (1978); Isen and Levin (1972).

Getting cookies, free stationery, and other mood boosters has been found to have a similar effect.See, for example, Isen et al. (1976) and Isen and Levin (1972).

Happier people are more cooperative,Carnevale (2008).

Happier people are more cooperative, trusting,Kaliterna‑Lipovčan and Prizmić‑Larsen (2016).

Happier people are more cooperative, trusting, and generous,Isen et al. (1976); Isen and Levin (1972).

Happier people are more cooperative, trusting, and generous, and they volunteer more,See Lawton et al. (2021) for a recent discussion and exploration of the relationship between happiness and volunteering.

Happier people are more cooperative, trusting, and generous, and they volunteer more, though, as always, the evidence is somewhat mixed.Aknin and Whillans (2021); Weiss-Sidi and Riemer (2023).

Reciprocally, happier people tend to be less critical and appear less anxious.Gardiner et al. (2022).

There is some evidence that being happier leads to greater productivity,Oswald et al. (2015). Note that there remains active debate in this area.

There is some evidence that being happier leads to greater productivity, though being too happy can actually decrease ambition in the work domain.Oishi et al. (2007).

Generally, happiness seems to make people more pro-social, likable, and popular.Boehm and Lyubomirsky (2008).

Happier people are more extrovertedMargolis et al. (2020).

Happier people are more extroverted and more likely to seek and build social relationships, developing more robust support networks.Diener et al. (2015).

They tend to be more likely to participate in social activities.Robinson and Martin (2008).

…wide array of fitness-good results: “Positive moods produce desirable outcomes in several areas: physical health, including fecundity and longevity; sociability and supportive social relationships; and coping and resource building, including forethought, planning, and creativity.”Diener et al. (2015), p. 237. See also Lyubomirsky et al. (2005).

Happier people smile—but not laugh—more and are more playful,Gardiner et al. (2022).

Indeed, everyone prefers being around happy people, rating them as more appealing than dour folks.Gardiner et al. (2022).

Feel 58: Joyful and Euphoric

That night, seeing the whole team come out to celebrate my birthday, well…Joy, like so many feels, has received only limited research attention.Watkins et al. (2018) claim that to that point, “outside of a handful of studies, this emotion has rarely been empirically examined as a discrete emotional state” (p. 522) and that it is “the least studied of the positive emotions.” Johnson (2020) echoes this view, writing: “Surprisingly little work has been done…on joy” (p. 5). Having said that, Dearborn wrote a treatise on the topic, way back in 1899, a dissertation subsequently published in The Psychological Review. I don’t draw on this material here because, candidly, I found the prose impenetrable.

Joy has been tricky for scholars to pin down or even define.Johnson (2020).

There is some consensus that joy is felt in response to a specific—and good—outcome or episode, as opposed to a more general positive sense, as in happiness or a sense of well-being.Watkins et al. (2018) find that joy “can also be experienced as a more subtle enduring state” (p. 534), so this distinction might not be a rigid one.

Joy measures significant progress towardFredrickson (1998).

One important element is the difference between outcomes and expectations.See Johnson (2020) for a brief discussion.

In 2016, a fan of the Chicago Cubs, the World Series winner after a century-long drought, said the team’s victory was “the most amazing feeling in the world.”Quoted in Watkins et al. (2018).

These feelings likely exist to reinforce the learning that comes with play, which itself is practice for the real world.Fredrickson (2009).

And joy can come after but also before reaching some goal.See Meadows (2014) for an exhaustive account.

Similar to pride, joy often—though not always—motivates energetic movement, possibly to signal one’s success, as in jumping for.Dearborn (1899) highlighted this as a key part of joy. Ok, I did try to work through it. More recently, see Watson et al. (1999).

First, euphoria certainly resembles joy—but on steroids or, perhaps, on dopamine.Di Chiara (2002). Generally, emotions researchers have historically claimed that “pleasant emotional experience is somewhat less differentiated than unpleasant emotional experience” (Ellsworth & Smith, 1988b, p. 326).

Second, there is relatively little relevant research on euphoriaThere is some work on euphoria from a clinical perspective, but my focus is on the non-pathological kind.

Euphoria comes from running,For a recent retrospective, see Whitehead (2016).

Euphoria comes from running, team sports such as rowing,Cohen et al. (2010).

Euphoria comes from running, team sports such as rowing, and expertly executed dance,Tarr et al. (2015).

The difference between joy and euphoria is largely one of magnitude, though some have argued there is a difference in kind.Watkins et al. (2018).

…showed that if you let rats press a lever to get a little jolt to the brain’s pleasure center, they’ll press the lever thousands of times per hour, forsaking eating, drinking, and even sex.Olds (1958) is the classic source.

Deep brain stimulation can similarly directly grant pleasure.Haq et al. (2011).

More importantly, some recreational drugs do so, and with greater duration, helping to explain addiction.Di Chiara (2002).

Attention is variously defined by psychologists, but at its core, the notion of attention turns on the fact that it is limited:The ideas I discuss in this introduction go back a long way, and I therefore cite classic work as opposed to more recent scholarship. While there have been developments in all of these areas, the basic ideas have not changed a great deal. For classic work on attention, see Miller (1956), Broadbent (1958), Treisman (1960, 1969), Kahneman (1973), and Posner (1980).

The fovea, where the densest sensors are located, can only be directed, courtesy of our eyeballs, to one location.Hubel and Wiesel (1962).

Optimal looking constitutes, then, a crucial adaptive problem.Treisman (1964).

If we start eavesdropping on the discussion behind us, we might not be able to converse meaningfully with the person we’re talking to.Cherry (1953); Moray (1959); Treisman (1960).

So-called working memory, for example, is like a buffer where information can be processed, but there is a limit.See Baddeley and Hitch (1974) and Miller (1956).

That feeling of not knowing is metacognitive, a thought about your own thoughts.Flavell (1979).

Feel 59: Effort

…“ego depletion theory,” the notion that some mysterious and unnamed substance got used up when we were doing repetitive tasks, such as, say, crossing out the letter “e” in every word in a sentence.Baumeister et al. (1998).

This idea was everywhere, including the Oval Office.In 2012, Barack Obama, embracing the ego depletion view, said, “I’m trying to pare down decisions. I don’t want to make decisions about what I’m eating or wearing…the simple act of making decisions degrades one’s ability to make further decisions.” This was published in Vanity Fair on September 11th, in a piece by Michael Lewis.

Some follow-up work proposed that the mysterious substance used up was glucose, which I thought was even more absurd.I responded to this idea in Kurzban (2010). It’s available here: https://journals.sagepub.com/doi/10.1177/147470491000800208. This paper responds to Gailliot et al. (2007). I asked for the data from Gailliot et al. (2007) and received some of it but was told that some of the data “have been corrupted.” I let various people know that an author was unable to produce data requested from a recent paper and…nobody cared. I’ll add my usual remark here that academia almost never punishes such lapses, which is one reason that the social sciences have advanced so slowly and why the replication crisis continues to plague the field.

While ego depletion might have appealed to Barack Obama and the indefatigable John Tierney,Baumeister and Tierney (2012).

While ego depletion might have appealed to Barack Obama and the indefatigable John Tierney, the idea has essentially been laid to rest in psychology.In a Psychology Today post in December of 2020, Elliot Berkman (2020) writes, “To their great credit, some of Baumeister’s collaborators, Kathleen Vohs and Brandon Schmeichel, and others appear to have finally ended this debate. They accomplished this by conducting one of the most thorough and convincing studies I’ve ever seen.” See Vohs et al. (2021). They write that “the data were 4 times more likely under the null than the alternative hypothesis. Hence, preregistered analyses did not find evidence for a depletion effect” (p. 1567). I mean, that’s pretty much that, right? Still, having said that, rumors of the demise of ego depletion might be exaggerated. Work on the topic is still being published. See Baumeister et al. (2024). They claim that the pattern of findings on which the initial theory was based “has now been well established” and that the “simple initial theory has been refined to emphasize conservation rather than resource exhaustion” (p. 1). Ego depletion is an example of what I’ve called a zombie theory, an idea that just doesn’t seem to die. See also Carter et al. (2015) for a meta-analysis.

Having said that, there is still no scholarly consensus about effort, including what it is, what it’s for, or how to measure it.A recent paper by Hack et al. (2025), available at ResearchGate entitled A Hitchhiker’s Guide to physical and cognitive effort, states: “For centuries, researchers have tried to understand what effort is and how it shapes human behavior. Yet, despite its importance, there is no overarching consensus on what effort represents and how it should be measured.”

Executive systems, the parts of your brain that do fancy tasks such as planning, can only do one thing at a time.Miller and Cohen (2001).

Somehow, we tot up this cost—known in economics as an “opportunity cost”—as we are engaged in tasks.I laid these ideas out in Kurzban et al. (2013).

Recent research in cognitive neuroscience has vindicated the view that the opportunity cost perspective can be productively applied to understanding both the sense of effort and boredom.Agrawal et al. (2022).

Feel 60: Focused/In Flow

The feeling is all-consuming of one’s attention, allowing one to persist for long periods of time, often without the sense of expending effort or realizing how long one has been at it.Definitions vary. Abuhamdeh (2020), for example, points out how the idea is treated by different scholars. For example, there is not consensus that the experience need be enjoyable. For the classic statement of these ideas, see Csikszentmihalyi (1975, 1990).

Some people refer to it as “being in the zone.”Kennedy et al. (2014). See Csikszentmihalyi (1990) for classic work.

Importantly, for the point of view I’m advancing, many people describe flow as “the subjective experience of engaging in just-manageable challenges.”Nakamura and Csikszentmihalyi (2002). The italics are mine.

Designers make the game more difficult as the player improves.When I played Civilization VI, I found King too easy but Immortal too hard, so I always chose Emperor.

Indeed, a significant body of research confirms that players are more likely to report the sense of flow when the challenge posed by the game fits their level of skill.Larche and Dixon (2021) and citations therein.

Further, when there is a good match, players are more likely to persist, as one would expect from what this feel is designed to motivate.Larche and Dixon (2020).

Players experience the greatest flow when their skill is high and the challenge is as well.Larche and Dixon (2020), p. 614.

…doesn’t justify continued effort, as we’ll see in the next chapter—and when the game is too difficult, players feel anxiety or frustration, the feels that motivate stopping because continuing isn’t likely to yield success.Larche and Dixon (2020). See also Nakamura et al. (2012).

Similar results have been obtained for the popular video game Tetris.Keller and Bless (2008).

Some research suggests that most people would prefer to play a game that they are likely to lose that matches their skill over a game that they are likely to win easily.Larche and Dixon (2021).

Feel 61: Bored

(Note on the chapter “Bored” as a whole)This chapter draws significantly from an entry on Living Fossils called “Digging into Boring.” The view endorsed here resonates with that of Bench and Lench (2013), who argue that “boredom motivates pursuit of new goals when the previous goal is no longer beneficial. Exploring alternate goals and experiences allows the attainment of goals that might be missed if people fail to reengage” (p. 459).

Boredom is a relational property.The source for the quote in this footnote is Bench and Lench (2013), p. 460.

Boredom is an unpleasant feel, a desire to do something other than whatever one is currently doing, which could be nothing at all.Eastwood et al. (2012).

Boredom is measuring how much less rewarding what one is currently doing is compared to alternatives.See Eastwood et al. (2012) for the idea that boredom has to do with one’s ability to use one’s attention in the service of some satisfying activity.

Hence, there is value in considering what rewarding opportunities exist.Along similar lines, Bench and Lench (2013) suggest that “boredom arises from the perception that the current situation is no longer stimulating, as reflected in diminishing emotional response to the situation. Boredom then organizes responses to this situation that encourage people to seek alternative goals and experiences…” (p. 461). It’s worth noting that this logic is parallel to that behind optimal foraging theory, which can provide a formal framework for investigating boredom. In that literature, the animal moves on to a new patch when the rate of return of the present patch is less than the expected value of moving to a new one, accounting for the cost of switching patches.

Interestingly, people who are more prone to boredom are more likely to develop a gambling problem.Mercer and Eastwood (2010) find that “boredom is distinctly related to gambling problems, above and beyond its overlap with sensitivity to reward” but note that they also suggest that “individuals gamble in order to increase arousal, rather than to avoid the negative affect associated with boredom.”

Feel 62: Distracted

This time, without counting the passes, you see it clearly—a person in a gorilla suit enters from the right, moves to the center of the screen, thumps their chest, then exits stage left.Simons and Chabris (1999). Many subjects don’t notice the gorilla, though some do. The percentage varies somewhat depending on the sample.

As we have seen, attention is limited.Cowan (2017).

In high-focus tasks, some people fail to notice even loud sounds, depending on how engaging the task is.Lavie (2005) notes that “distractors are simply not perceived when the perception of task-relevant stimuli under high load consumes all or most of the available capacity” (p. 76).

The feeling of being distracted is this awareness, the measurement of the gap between how focused you want to be and how focused you actually are.This is my view, and I didn’t find a great deal of support for this position—or, at least, support for using the term exactly in this way—in the scholarly literature. Take this feel with more than just the usual amount of salt.

However, distraction can sometimes be welcome—people experiencing grief often seek distractions to escape perseverating on their loss.See, for example, Shear et al. (2013) and Nolen-Hoeksema (2001).

Students have always struggled to maintain focus, but omnipresent digital devices intensify the challenge.See especially Jon Haidt’s work on this, including his recent book The Anxious Generation.

The more complex the perceptual task, the fewer external distractions are noticed.Lavie (2005).

Studies show that individuals who report more task-unrelated thoughts make more errors and respond more slowly in lab tasks.See Hobbiss et al. (2019) and citations therein.

However, it’s worth pointing out that some research suggests that brief mind-wandering can enhance creative problem-solving.Hobbiss et al. (2019).

The human mind consists of a large number of modules, many of which run in the background, filtering information from outside—the senses—and inside—other modules.For my view, see Kurzban (2011).

Not only that, but the competition in the modern market for attention means that the firms that have done the best job at capturing our attention—looking at you, TikTok—have prospered.See The Distracted Mind, by Gazzaley and Rosen, for a thorough recent treatment.

One study—using iPhones, of course—found that people were actually paying attention to what they were doing only about half the time; the rest of the time their minds were wandering.Killingsworth and Gilbert (2010).

Despite hands-free and voice-activated systems, distraction remains a major cause of traffic fatalities.Strayer and Drews (2007); Strayer et al. (2015). See data from the National Highway Traffic Safety Administration for additional details. See https://www.nhtsa.gov/press-releases/2022-traffic-deaths-2023-early-estimates.

Feel 63: Impatient

This idea makes some sense—good things come to those who wait and all that—though recent work has called this claim into question.Watts et al. (2018).

In one study, blue jays only had to wait a few seconds to get two pellets of food rather than one, yet they didn’t.See Burnham and Phelan (2021) for a recent excellent and readable account of discounting in non-humans and lessons for psychology.

Impatience, then, motivates consuming the benefit, whether in the form of a marshmallow or a sexual partner.See Fudenberg and Levine (2006).

Feel 64: Curious

First, it has been suggested that “curiosity, the desire to know, is a fundamental driver of human behavior.”Hsiung et al. (2023), p. 1. See also Berlyne (1960) and Loewenstein (1994).

Nonetheless, in 2009, a group of researchers wrote that “Despite its importance, the psychological and neural underpinnings of curiosity remain poorly understood.”Kang et al. (2009), p. 963.

Six years later, a different team wrote, “Curiosity is a basic element of our cognition, but its biological function, mechanisms, and neural underpinning remain poorly understood.”Kidd and Hayden (2015), p. 449.

Years later, and bringing us close to the present, yet a third group of scholars wrote, “Precisely how the curiosity-inducing mechanism operates in biological organisms is poorly understood.”Ten et al. (2022), p. 53.

Curiosity, then, is measuring the benefit of gaining new information, taking into account the probability of getting it and the cost of the search,I’m not sure about this. It could be that the feeling does not take the probability or the cost into account, but the decision to seek the information does take both into account. That is, one can be very curious about a fact that is unknowable or very costly to discover. See Sharot and Sunstein (2020) for an excellent discussion.

So we’re managing our future happiness in the medium termSharot and Sunstein (2020) distinguish among motives when it comes to curiosity, breaking it into three. There is the instrumental value of information, which is useful for decision-making; the hedonic value, how much information will make us happy; and the cognitive value, how much information aids understanding. It seems to me that the cognitive value is often either useful or happy-making, so I think two categories suffice.

While many people rally to the aid of someone in dire need, others don’t.See Liang et al. (2022) for a discussion and additional sources.

…pay to get the answer to these moderately difficult trivia questions even though if they were patient and waited for the end of the experimental session, they would be given the answer for free.I am basing this description on the account in Kidd and Hayden (2015), p. 5. This is a rare case in which I was unable to get my hands on the original, in this case the piece by Camerer and collaborators.

Feel 65: Surprised

In this experimental design, researchers leverage the fact that infants become bored with (habituated to) a stimulus that is repeatedly presented.Baillargeon et al. (1985).

In this, they are just like adults, who also look longer at events that are surprising compared to those that are not.Needham and Baillargeon (1993). See also Horstmann and Herwig (2015).

…goose will grow up to be a goose but never a duck), to psychology (people tend to look at things they want), to sociology (people will be loyal to their groups), and so on.See, for example, Gopnik and Wellman (1994), updated in Gopnik and Wellman (2012).

If an organism experiences an association that it did not expect—the ringing of a bell is followed by the appearance of food, say—it learns this association, driven by the surprise it experienced.Rescorla and Wagner (1972).

This fact explains signature features of surprise, especially the motivation to stop movement and stare—or listen or sniff or ask questions, depending on the nature of the surprise—as one is gathering more information.Reisenzein et al. (2019).

When we are surprised, our attention is automatically turned to figuring out the cause of the discrepancy.Reisenzein et al. (2019).

This fact might also explain why our pupils dilate, hungry to take in more information.Reisenzein et al. (2019).

In many cases, surprise specifically motivates determining the cause of the surprising observation.See, among others, Pyszczynski and Greenberg (1987).

The feeling of surprise stops us, interrupting whatever we were doing to devote time, attention, and our powers of reasoning to update our schemas appropriately.Oatley and Johnson-Laird (1987).

…overarching evolutionary function of the surprise mechanism…can be described as follows: (1) to detect schema-discrepancies and, once they have been detected, (2) to enable and motivate the short-and long-term adaptation to them.”Reisenzein et al. (2019), p. 53, italics original. See classic work by Rescorla and Wagner (1972) and subsequent refinements.

The jaw drop is a bit mysterious—but see the next chapter, on awe—and, in any case, there is evidence that the canonical surprise face is, in fact, somewhat rare.Reisenzein et al. (2013).

Feel 66: Awe

…researchers working on this question, suggests that awe “shifts our minds from a more reductionistic mode of seeing things in terms of separateness and independence to a view of phenomena as interrelating and dependent.”Keltner (2023). Another suggestion is that awe “integrates us into the systems of life” and “connects our individual selves with the vast forces of life.”

What’s the function?This is available at http://www.markrkelly.com/Blog/2023/02/07/dacher-keltner-awe-the-new-science-of-everyday-wonder-and-how-it-can-transform-your-life/.

Consider, in this light, the facial expression and characteristic behavior of people in awe.Darwin (1872).

Feel 67: Skeptical/Doubtful

The philosopher shakes his head and says, “All we really know is that at least one sheep in Scotland is black on one side at least some of the time.”I did not make this up. Wikipedia credits it to Ian Stewart in his book Concepts of Modern Mathematics. I could not verify this myself, but I have no reason to doubt it. I have modified the version as it appears in the Wikipedia entry: https://en.wikipedia.org/wiki/Mathematical_joke#cite_ref-17

Skepticism is useful, but it has to be just the right amount.I tried to get at this in a short chapter some time ago: Kurzban (2007b).

Remember that evolution selects for design to signal information only when it benefits the signaler.Johnstone (1995). See Krebs and Davies (2009) for the textbook on this topic.

Behaviors that betray information that hurts the organism if others know it are selected against.See sources in the preceding endnotes and also Grafen (1990).

Having said that, as organisms go through life, only a select few other organisms are cooperating with them.See, for example, West et al. (2007a).

All of this is made much more complicated by language, which allows people to package ideas into words.Pinker (1994).

If someone tells you that you will experience bliss if you give them all your money, well, best not accept this as truth.On this topic, see Cosmides and Tooby (2000a), for an excellent discussion that adds much to the ideas in this chapter.

…to learn important local facts—how to make and use tools, which animals are dangerous, and so forth—from other people, as opposed to learning by yourself, which can be both time-consuming and even potentially deadly.Boyd et al. (2011).

…culture, the process that got us from the wheel to the moon in a few thousand years, to say nothing of arriving at democracy, depends on the accumulation of information from others over time.Boyd and Richerson (2005). See more generally work in the tradition of these two scholars.

…others about a lot of facts—that animal is called a cow—but at least doubt, if not flat out reject, other things that people might say—I’m from the government, and I’m here to help you.Kurzban (2007b).

Some scholars argued that this predicament led to the evolution of what is called “epistemic vigilance,” evaluating incoming information for its reliability, credibility, and overall truth.Sperber et al. (2010).

One of the most important is whether accepting the information as true is strategic: Does accepting it likely change our behavior in a way that might help or harm us?Some scholars have suggested that humans are relatively trusting by default. That might be due to the fact that so much information we come across is not all that relevant to us. As Sperber et al. (2010) put it: “Epistemic vigilance involves a processing cost which is likely to be kept to a bare minimum when the information communicated is of no possible relevance to oneself” (p. 363). I wrote a little bit about this idea in a post called Thuggistry, available at https://thelivingfossils.substack.com/p/thuggistry.

Research has shown that even young children are skeptical learners and will resist adopting a belief if adults make statements the child thinks are wrong in some way.Pea (1982).

Even young children use a speaker’s past history when evaluating how much they trust what they say.Ganea et al. (2011).

…as Lie to Me in which some characters are able to distinguish truth from lies, the best research in this area indicates that the untrained average human isn’t all that good at detecting lies.Bond and DePaulo (2006); DePaulo et al. (2003); Vrij et al. (2017).

Most studies indicate that humans’ ability to detect lies in the laboratory is barely above chance: 54%.Bond and DePaulo (2006).

And while people can be trained to get a bit better at detecting falsehoods, even training doesn’t help all that much.See Vrij et al. (2017) for a meta-analysis and discussion. They report rates of up to 67% for lie detection and truth detection.

We humans are, however, a bit better at detecting lies from those close to us.Sternglanz and DePaulo (2004).

The difficulty lies in distinguishing normal speaking variations—caused by anxiety, social context, or individual differences—from cues specifically tied to deceit.See DePaulo et al. (2003) for the classic work.

…of which we are skeptical with a kind of an asterisk or with a source tag—Jim said that his restaurant makes the best pizza—rather than the fact that the restaurant makes the best pizza.Cosmides and Tooby (2000a).

Feel 68: The Feeling of Knowing

…wraith of the name is in it, beckoning us in a given direction, making us at moments tingle with the sense of our closeness and then letting us sink back without the longed-for term.James (1893).

Analogously, the feeling of knowing is a measurement of the probability that you’ll eventually recover the searched-for memory.See Hills’ work on this, especially Hills (2006), Hills et al. (2012), and Hills et al. (2015).

This feeling motivates abandoning the search because the opportunity costs outweigh the expected benefits.Schwartz (2001).

Research has shown that when people express that they have this feeling in the laboratory, they are more likely eventually to be able to recover the sought-after information from memory.For classic work, see Hart (1965), Schacter (1983), and Schwartz and Metcalfe (1992). See also Koriat (2000), for a good account of the work to that point. More recently, see Schwartz et al. (2014).

Scientists using a technique called electroencephalography recently concluded that “our data support that [feeling of knowing] has a distinctive neural manifestation and is detectable from the brain…”Michalkova et al. (2024), p. 24.

Adults are similarly good at predicting their performance on math problems but much less so on problems requiring some sort of insight to solve.Metcalfe and Wiebe (1987).

Classic work in developmental psychology,Flavell (1970).

If one has the sense that one can recall something but doesn’t quite manage, the feeling motivates seeking the missing information.Metcalfe et al. (2017); Brooks et al. (2021).

…when it has gotten all the berries that are easy to get so that the value of staying at that berry bush is low relative to the benefit of moving to a new patch.See Hills et al. (2012) and Hills et al. (2015), for some experimental work on this.

Feel 69: Confused

…it, confusion, or “cognitive disequilibrium,” occurs “when an individual is confronted with obstacles to goals, interruptions of organized action sequences, impasses, contradictions, anomalous events, dissonance, incongruities, unexpected feedback, uncertainty, deviations from norms, and novelty.”D’Mello and Graesser (2012), p. 146.

Surveys of students engaged in tutoring sessions, for example, show that the most common emotion that learners feel is confusion.D’Mello et al. (2014).

This route, in which the source of confusion is resolved, has been called “productive confusion.”D’Mello and Graesser (2012). See also Rozin and Cohen (2003).

Resolving confusion leads to positive feelings, such as joy and delight,Di Leo et al. (2019). See also Gopnik (1998).

This has been called “hopeless confusion,” and this feeling might come after some preliminary attempts to resolve the confusion and eventually lead to disengagement.D’Mello and Graesser (2012).

In these cases, the feeling of confusion changes into feelings of frustration or boredom,Di Leo et al. (2019).

Confusion motivates making good choices about trying to resolve the discrepancy between one’s expectations and observations, trying to restore cognitive equilibrium.D’Mello et al. (2010).

Overall, despite the fact that confusion, generally, is experienced as a relatively negative feeling,Vazard and Audrin (2022), an excellent source on this topic, make this claim, citing D’Mello et al. (2014).

Overall, despite the fact that confusion, generally, is experienced as a relatively negative feeling, the evidence is that more confusion during learning is related to greater learning.See D’Mello et al. (2014), who review evidence supporting this claim and provide additional empirical support for it.

As scholars working in this area recently put it, “Confusion can be effective in promoting deeper processing and thereby increased learning gains.”D’Mello et al. (2014), p. 165.

Feel 70: Frustrated

Hinch found all of it “extremely frustrating.”According to a report by the LA Times: https://www.latimes.com/nation/nationnow/la-na-nn-colorado-shooting-computer-20150421-story.html.

Far from experiencing regret, Hinch was quoted by the Los Angeles Times as saying that “Angels sung on high,” and that the death of the computer was “glorious.”Reported by HuffPost, 4/22/2015, available: https://www.huffpost.com/entry/man-shoots-computer-eight-times_n_7119246.

The serious study of the topic began in 1939 with the “frustration-aggression hypothesis,”Dollard et al. (1939).

The serious study of the topic began in 1939 with the “frustration-aggression hypothesis,” which was the idea that frustration always led to aggression and aggression was always caused by frustration.See Williams (2009) for a brief review.

In any case, more recent work has focused on building a more nuanced view of the feeling.Interestingly, some of the best work teasing apart frustration and anger is in the marketing literature. See, for example, González‐Gómez et al. (2021), for a nice treatment.

A reliable way to induce frustration is to give subjects a set of anagrams to solve, some of which have, in fact, no solution.See Schneider et al. (1996). For the use of the method in neuroscience, see Pawliczek et al. (2013).

…more frustration do stop trying more quickly, and research using the tools of neuroscience has shown that these tasks activate the regions of the brain you might think would be involved, including the amygdala.Pawliczek et al. (2013).

For instance, when the goal someone is trying to achieve is not especially significant to them, frustration is less likely to lead to anger.Lazarus (1991).

In fact, despite concerns that violent content leads to hostility, evidence from self-reports suggests that frustration causes a greater sense of hostility than violent content does.Williams (2009).

Anger is generally, though certainly not always, aroused only when there’s a person to be mad at.González‐Gómez et al. (2021). Study 1.

People feel more frustration when they perceive the situation to be unfair or arbitrary.Breuer and Elson (2017).

…frustration seem to be that one is trying to reach a goal but can’t for reasons they believe are beyond their control and unfair, whether the root cause is a person, circumstance, or object.González‐Gómez et al. (2021).

Feel 71: Uncertain / Certain

My sister winds up with more spare time.Schwartz et al. (2002). Generally, there are significant individual differences in this area. See generally the work of Barry Schwartz, especially his book, The Paradox of Choice.

In this work, there is a close relationship between people’s confidence in their answers and the likelihood that they are correct.Pleskac and Busemeyer (2010).

…“Another set of algorithms ranks these answers according to plausibility; for example, if dozens of algorithms working in different directions all arrive at the same answer, it’s more likely to be the right one.”I wrote about this in a blog post, archived here: https://web.sas.upenn.edu/kurzbanepblog/2011/02/28/modularity-my-dear-watson/ The Times piece is What is I.B.M.’s Watson, by Clive Thompson, on June 16th, 2010.

When researchers gave 3-year-old children the opportunity to answer questions or choose not to, the young subjects wisely chose to avoid answering questions that they recognized would be difficult for them.Bernard et al. (2015).

…adept at recognizing when they are or are not likely to be correct in answering questions that they will place bigger bets on questions they (correctly) judge that they will be better at answering.Hembacher and Ghetti (2014).

…species such as rhesus monkeys and dolphins selectively opt out of trials when the perceptual cues are indeterminate—a behavioral strategy that mirrors human tendencies to decline to make a decision when confidence is low.Smith et al. (2003).

(He did.) As a general matter, people don’t like uncertainty.See Carleton (2016) for a thorough review.

Research in physiology and neuroscience has shown that when faced with the unknown, there are physiological markers, such as increased heart rate variability and brain activation in regions associated with emotion, including the amygdala.Thayer et al. (2012).

Across many contexts, people fear the unknown; after all, what you don’t know can, in fact, hurt you.Carleton (2016) asserts that the perception that there is not enough information is aversive.

However, when the signal remains weak or ambiguous, the decision-maker delays commitment, allowing additional time for evidence to accrue.See Pleskac and Busemeyer (2010) for a discussion.

The feeling of uncertainty can also motivate more conservative decision-making, as people try to avoid making catastrophic mistakes when they are not sure they are getting it right.Rassin and Muris (2005).

Feel 72: Understanding

In his account of World War II,This vignette appears in Churchill’s book, The Second World War, Volume IV, The Hinge of Fate.

Such misunderstandings are the root of the quote, usually attributed to George Bernard Shaw, that “England and America are two countries separated by the same language.”Sources vary. The attribution to Shaw dates to 1942 in Reader’s Digest. Oscar Wilde made a similar remark in a short story, published in 1887.

They felt fluent, as cognitive psychologists say.See, for example, Oppenheimer (2008).

Instead of moving it on the board, I would move it in my head and visualize, Oh, that puts my rook in danger of capture in two moves.MacGregor et al. (2001). See the movie The Queen’s Gambit starring Anya Taylor-Joy for a vision of this process.

Research has shown that in the absence of confirmation of understanding, we rely on a variety of cues, especially familiarity and fluency.Oppenheimer (2008); Boehm (1994).

Importantly, this illusion was much stronger for explanatory knowledge (how things work) than for factual knowledge (simple facts or figures).Rozenblit and Keil (2002).

Psychologists have similarly documented that students can feel confident about material they’ve studied, only to perform poorly on tests.There is a tension here with the finding that people are pretty good at knowing what they know, as discussed in the feeling of knowing chapter. The truth of the matter, as always, is that it’s complicated.

But later, when trying to recall or apply the information, they realize a lot didn’t stick.Glenberg et al. (1982).

A similar pattern has been observed in the context of people trying to explain how political policies work.Fernbach et al. (2013).

Think of Molière having a medical student “explain” that the reason opium makes people sleep is because of its “soporific quality.”See Le Malade imaginaire by Molière.

Some have argued that at least some of the modern social sciences have fallen prey to this sort of mistake.Trout (2002).

Gerd Gigerenzer convincingly argued that some psychologists treat one-word labels such as “availability” or “representativeness” as explanations.Gigerenzer (1996).

Feel 73: Inspired

Here, then, I had at last got a theory by which to work…The text of the autobiography, from The Life and Letters of Charles Darwin, as cited by the Friends of Charles Darwin website (n.d.).

This is astonishing…”Topolinski and Reber (2010), p. 403. Interestingly, as late as 1981, scholars claimed there was no evidence for “insight,” a near synonym of the kind of epiphany Darwin claimed to experience. See Weisberg and Alba (1981). Metcalfe and Wiebe (1987) provided evidence of sudden (and pleasant) insight in the laboratory. Similarly, as recently as 2016, Shen et al. (2016) claimed that “research regarding the concept of an ‘Aha!’ experience has been largely neglected” (p. 282).

moment is when a new idea, solution, or understanding comes, often suddenly, into consciousness.Definitions vary. See Salvi (2023).

experiences can be found in many different contexts, including solving puzzles, answering riddles, or getting a joke.Oh et al. (2020).

experience has four key pieces: The solution is sudden, the solution is felt to be correct with great confidence, it feels pleasant, and what was hard now seems easy.Again, views differ, but I find this list relatively persuasive. See Topolinski and Reber (2010). See also Metcalfe and Wiebe (1987) for classic work on the topic and a nice historical summary.

Research supports the view that people experiencing insight simultaneously experience a feeling of certainty.See Shen et al. (2016), Study 1, for example.

experience comes a sense of ease.See Shen et al. (2016), Studies 1 and 3.

Insight restructures or rearranges ideas and concepts, revealing a new framework.Luo and Knoblich (2007).

The theory is so clarifying that biologist Theodosius Dobzhansky asserted that “Nothing in biology makes sense except in the light of evolution.”Dobzhansky (1973).

Evidence suggests that insight arises from significant processing of which the person is relatively unaware.Kounios and Beeman (2009). See also Schooler et al. (1993) and Schooler and Melcher (1995). In terms of brain structures, some evidence points to aha! experiences activating structures such as the amygdala and the hippocampus. See, for example, Zhao et al. (2013). Salvi (2023) suggests that “insight below awareness processing might be explained by the involvement of subcortical areas responsible for learning, alertness, and emotions which are evolutionary more ancient than the cortex and it involves areas of the cortex responsible for information integration…” This quotation is from the abstract and I have left “evolutionary” as they rendered it.

Having said that, there is ongoing scholarly debate about whether all insight experiences are sudden.Shen et al. (2016), for example, reported that they “did not directly replicate the important role of suddenness in the ‘Aha!’ experience” (p. 294).

That feeling is evolution’s way of motivating you to move on and, if possible, do it again.Neuroscience work has shown that insight activates the dopamine system, as one might expect (Salvi, 2023).

Feel 74: Satisfied

Videos of machines perfectly harvesting rows of crops, leaving no stalk standing.See 2:15 in this video for very satisfying scallion harvesting: https://www.youtube.com/watch?v=laFbfvA3LhQ The video contains other similarly satisfying examples.

In The Office,This occurs in Season 4, Episode 5.

In The Office, the team is watching a DVD logo bounce around on the screen, and, almost always, it just misses,You can find this on YouTube: https://www.youtube.com/watch?v=QOtuX0jL85Y&ab_channel=TheOffice.

Even if it’s not something we’re intimately familiar with—a field of scallions, say—we get a lot of help because we are intimately familiar with visual properties such as symmetry, repetition, uniformity, and closure.So-called “Gestalt Psychology” is a good place to look for these perceptual primitives; Wagemans et al. (2012).

So satisfaction has what seems to be something of an uncanny valley.Mori et al. (2012).

But as it gets close to right but just misses, it’s very unsatisfying and then leaps up to very satisfying as it matches the solution state.The careful reader will notice that I barely cited any research. It was oddly difficult to find any good work (in my view) on this topic. So all of these ideas are my own musings, though it’s very possible that others have said similar things and I didn’t dig up the work. In any case, as with many feels, this explanation should be taken with a bit more salt than others because it doesn’t rest on firm scholarly empirical foundations.

Monera

…paper in Science proposing the five Kingdom structure that I was being taught was, at that time, relatively new, having been published only in 1969, the same year I myself came into the world.Whittaker (1969).

I call it “Monera” as an homage to the classification system I learned in high school.Debate continued after that point about the details of how to break the biological world into Kingdoms. See, for example, Woese et al. (1990).

Artificial Sweeteners and Hallucinogens But first, let’s talk about fish and logic.Some of this material appeared in the Living Fossils post on Sneezing (July 31, 2024).

This idea is often referred to as “mismatch.”See especially Burnham and Phelan (2000).

People who have lost a limb nonetheless report still sensing it, often painfully.Ishigami and Boctor (2024).

When you pun, you put me to work.See Steve Pinker’s (1997) account of humor in How the Mind Works.

It turns out that this feeling, which I call “cute crushing,”Aragón et al. (2015) refer to this as “cute aggression.” I wrote about this in August of 2025 on Living Fossils.

It turns out that this feeling, which I call “cute crushing,” is an actual thing, so much so that there’s a word for it in Filipino, gigil.Aragón et al. (2015).

One proposal is that some stimuli are so overwhelming—in this case, overwhelming cuteness—that people recruit the opposite of the feeling to deal with the overload,Aragón et al. (2015). But see Stavropoulos and Alba (2018) for an explanation grounded in neuroscience.

There’s spirited academic debate about what’s going on with yawning, which I will, as I have with most such debates, ignore and relegate to an endnote.See Jin (2022) for a recent review. Proposals include something to do with waking and sleeping, getting more oxygen, cooling the brain, and relieving stress.

Indeed, this debate is so wide-ranging that one prominent scholar collected twenty different ideas about what the function of yawning might be.Smith (1999), Table 1.

One proposal is that yawning is a prelude to activity: getting ready for the day in the morning and preparing to persist into the evening.Smith (1999).

Many animals yawn just before their feeding time, as if getting ready to get down to business.Baenninger (1997).

…the one hand, that you have a memory of what you are experiencing, while on the other hand, you know that you couldn’t have—for example, when you’re visiting a place for the first time.See Brown (2003) for seminal work on déjà vu.

As with so many feels, debate continues about explaining déjà vu,Brown and Marsh (2010) suggest that, to that point, more than forty possible explanations were on offer.

As with so many feels, debate continues about explaining déjà vu, not least because it’s difficult to study in the lab and research has been unable to discover reliable triggers for it.Brown and Marsh (2010).

We olds have lots and lots to store and a whole bunch of memories to sort through when we’re trying to recall something or someone.Schacter (2001).

One possible explanation, with some evidence behind it, is that sometimes we come across a scene and some part of it matches something that we have indeed experienced, producing a sense of familiarity.See Brown and Marsh (2010) for a review of evidence for this and other possible explanations.

Now, normally, we get a sense of familiarityYes, I could add the sense of familiarity or, for that matter, the sense of novelty as feels. They are feels, but they don’t seem, to me, to have a motivational piece, so I omit them.

Using the language of modularity, of which I am fond, it’s as if one module is saying something like, “I have seen this before” or “I know what is about to happen,”Cleary and Claxton (2018).

This feel is complicated, a mix of both a positive quality—that was a good time—with a negative quality—I miss those days and am sad they are gone.Newman and Sachs (2023).

…down what nostalgia might be measuring, in part because the feeling comes about in response to a wide array of circumstances, including everything from feeling lonely to certain kinds of music to bad weather.See Newman and Sachs (2023) for additional detail and citations.

Some evidence suggests that people induced to feel nostalgia are, temporarily, more trusting and more prosocial.Stephan et al. (2014).

Having said that, as with so many feels, the evidence remains frustratingly mixed.Newman and Sachs (2023).

For instance, when people experience nostalgia about past sexual relationships, they show less satisfaction with their present one.Newman and Sachs (2023).

This fear measures how great it would be to be at the party we’re mulling attending and motivates us to get into the shower and get there.Accounts vary to some extent. My view accords most closely with the recent work by Lejarraga and Sákovics (2025). In their review, Tanhan et al. (2022) define it strictly as a motive: “Fear of Missing Out can be defined as the constant desire to follow the exciting and glorious lives of others through the internet and a state of constant anxiety about it” (p. 74, my italics). See also Przybylski et al. (2013) and Gabillon (2020).

Further, one prominent scholar of emotions put anticipation in his list of eight primary emotions.Plutchik (1980b).

Paul Ekman, who focused on facial expressions, didn’t include anticipation in his list of basic emotions,Ekman (1999).

This is the feeling that you get when you see something especially moving or inspiring, often an act of generosity, sacrifice, courage, skill, forgiveness, or unity.Haidt (2000).

Some scholars have argued that if you see other people behaving well, it’s a good sign that it would behoove you to do so.Sparks et al. (2019).

Indeed, research suggests that people who feel elevation are motivated to do good themselves.Schnall et al. (2010).

Finally, as is well known, Zeus gave Pandora a jarSee Mythos by Stephen Fry. He argues, with some justice, that it was a jar (pithos, according to Hesiod), not a box.