Evolutionary Psychology (book)

— The New Science of the Mind

Misunderstandings of evolutionary psychology

• Mechanisms are genetically determined
• Mechanisms cannot be changed
• Current mechanisms are optimal

Evolutionary hypotheses are falsifiable

Evolutionary hypotheses, when formulated precisely, are highly testable and eminently capable of being falsified when the evidence fails to support predictions derived from them (see Ketelaar & Ellis, 2000, for an excellent discussion of the issue of falsifiability).

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Mechanisms are adaptions

• Defining it by usefulness, probability, and only when necessary
  

  adaptation is invoked not merely to explain the usefulness of a biological mechanism but to explain improbable usefulness (i.e., too precisely functional to have arisen by chance alone) (Pinker, 1997). Hypotheses about adaptations are, in essence, probability statements about why a reliable, efficient, and economic set of design features could not have arisen by chance alone

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• VS physical law, no need to invoke an ‘adaption’
• Developmentally timed (not at birth)
  

  The developmental timing of the emergence of fears, in short, seems to correspond precisely to the onset of different adaptive problems—different forms of threat to survival. This illustrates the point that psychological mechanisms do not have to show up at birth to qualify as evolved adaptations. The onset of specific fears, like the onset of puberty, reflects developmentally timed adaptations.

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Mechanisms are problem-specific

• not general purposes and content-free
  

  Although the mind could be divided in an infinite number of ways, most of them would be arbitrary. A powerful non-arbitrary analysis of the human mind is one that rests on function.

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  There is no such thing as a general adaptive problem (Symons, 1992). Because adaptive problems are specific, their solutions tend to be specific as well.

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• Analogy: Swiss army knife
  

  The carpenter gains flexibility not by having one “highly general tool” that can be used to cut, poke, saw, screw, twist, wrench, plane, balance, and hammer. Instead, the carpenter gains flexibility by having a large number of highly specific tools in the toolbox. These highly specific tools can then be used in many combinations that would not be possible with a single highly “flexible” tool. Indeed, it is difficult to imagine what a “general” tool would even look like, since there is no such thing as a “general carpenter’s problem.” Similarly, humans gain their flexibility from having a large number of complex, specific, functional psychological mechanisms.

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• More tools = more flexibility
  

  Most of us holds that having a lot of innate mechanisms causes behavior to be inflexible. In fact, just the opposite is true. The more mechanisms we have, the greater the range of behaviors we can perform, and hence the greater the flexibility of our behavior.

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Aversion to disease

• Pathogen disgust
• Neophobia: aversion to new foods
• Pregnancy sickness: prevent toxins & abortion

Hunting

• Male parental investment (provisioning theory, high calories effectively brought back home)
• Strong male coalitions
• Success highly variable → sharing beneficial & reciprocal alliance
• Sexual division of labor & Sexual Dimorphism
• Stone tool use (killing & separating)

Environmental preference

• Mimic comfortable sensation under forest canopy
• Prefer views & vistas
• Dislike basements

Aggression (genocide)

• Gain access to resources, power & sex
• Deter future aggression, infidelity
• Defense

Unification of fields ^0fd026

• Cognitive psychology
  • Challenges assumptions: general purposes, ignoring content (artificial stimuli)
    • Successful solutions differs from domain to domain
    • Cannot understand functions without knowing the problem
    • Constrain search space of behaviors
  • Limited capacity of attention/memory: content-specific
  • Cognitive Tendencies & ecological rationality: evolved for ancestral environments
    • Base rate vs probability, cars vs snakes
• Language
  • Exchange of info about the physical & social world (gossip, contracts)
  • Machiavellian influence/manipulate others
  • Reproductive advantage
• Intelligence
  • ‘Deadly innovations’ create novel hazards
  • Subduing natural forces led to selection from social competition
• Social psychology
  • Traditional: the ‘what’, phenomenon-oriented
  • Evolutionary: the ‘why’, relationship-oriented
    • Inclusive fitness (kin)
    • Sexual selection & conflict
    • Parental investment & offspring conflict
    • Reciprocal altruism & punishment
• Moral emotions
  • Traditional: ‘reasoning’ are in fact fabricated or instinctual
  • Evolutionary: explains the problem-solving
    • Incest: prevent inbreeding
    • Anger/Revenge: punishes/deters cheaters
    • Embarrassment: appease
    • Shame: prevents ostracism
    • Guilt: confession & apologies
    • Gratitude: prosocial
    • Sympathy: altruism
    • Us vs them: justify & defense against violence
  • Reproductive success by sexual selection (virtues advertised)
    

    In sum, moral emotions might serve as “commitment devices” that promote prosocial deeds, reparation of harm, and punishment of cheaters, all while signaling to others that one is a good coalitional ally.

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• Developmental psychology
  • Facing predictably different adaptive problems at various points in their lives
  • Life-history strategies
    • Experiential calibration to the environment
    • Parent absence:
      • Untrustworthy, unreliable, bonds not enduring
      • Earlier sexual maturation, initiation, frequent partner switching - many offsprings, little investment
• Personality psychology
  • Flexible niche picking based on position or observation - low heritability
  • Frequency-dependent polymorphisms Fluctuating Selection - high heritability
    • Pros & cons to all, selection can favor & maintain diversity
    • E.g. Psychopathy, exploiting trusting norm
  • Condition-dependent
    • Calibrated to recurrent features of both the environment & evaluation of self (e.g. body type)
    • Exact strategies not direct heritability, but reactive heritability
• Mental disorder
  • Dysfunction: mechanism not doing its intended job
    • Types: under/over-activation, wrong context, not coordinating with other mechanisms
    • Causes: variants co-occur, mutations
  • Erroneously thought to be dysfunctional ^b101f4
    • Discrepancy between ancestral & modern environments Reasons for Tendencies
    • Once-thought disorders might serve adaptive functions
      • Depression
        • Disengage from hopeless strategy, conserve energy, motivate new paths
        • Deflates ‘blind’ optimism, objectively reassess
        • Elicit help
      • Anxiety: cautious & attentive, costly false alarms still less ‘costly’ than death
      • Paranoia: detecting & avoiding threat
    • Masking symptoms may thwart natural healing process Treating Adaptive Symptoms
• Culture
  • Causal explanation needed, similar to Morality
    • Within-group similarities + between-group differences
    • Labeling on its own ≠ explanation
    • Combining with biology, not competing
  • Evoked culture (tanning)
    • Conditional activation of universal evolved mechanism
    • E.g. variance of food supply ↔︎ sharing (shaming stingy)
    • E.g. pathogen prevalence ↔︎ importance of physical attractiveness, conformity to social norms
  • Transmitted culture
    • Relies on evolved mechanisms that regulate attention, memory, communication
    • Conformity bias, prestige bias
    • E.g. Religion: byproduct of non-religious functions
      • Hyperactive agency detection, Teleology
      • Mentalization: imbue deities with motives & desires
      • Longing for a caretaker
      • Defense against meaninglessness
      • Costly signaling to gain entry to the group
      • Emotionally arousing rituals transmitted due to attention-grabbing nature
      • Coalitional psychology to minimize within-group conflict
  • GxC coevolution
    • E.g. diary product ↔︎ lactose tolerance
    • Reliance on cumulative culture ↔︎ culture learning & teaching > individual trial & error
  • Art & the
    • Artificial stimulation of a host of evolved mechanisms
    • Display hypothesis: competing in different mating arenas

Select Quotes

Dedication

Charles Darwin Francis Galton Gregor Mendel R. A. Fisher W. D. Hamilton George C. Williams John Maynard Smith Robert Trivers E. O. Wilson Richard Dawkins Donald Symons Martin Daly Margo Wilson Leda Cosmides John Tooby

Preface

Today that gap has closed considerably, because of both conceptual breakthroughs and an avalanche of hard-won empirical achievements. Many exciting questions still cry out for empirical scrutiny, of course, but the existing base of findings is currently so large that the problem I faced was how to keep this book to a reasonable length while still doing justice to the dazzling array of theoretical and empirical insights.

And to fhink that ghere are pessimists crying out about how we know nothing...

Part 1: Foundations Of Evolutionary Psychology

1. The Scientific Movements Leading To Evolutionary Psychology

As Dawkins (1982) calls it, “the argument from personal incredulity,” is not good science, however intuitively compelling it might seem.

The ethology movement was in part a reaction to the extreme environmentalism in U.S. psychology.

We have our innate natures

The inclusive fitness revolution marshaled a new era that may be called “gene’s eye thinking.”

Selection operating on individual differences within a group, in other words, undermines the power of selection operating between groups.

The problem is how to determine which attributes of organisms are adaptations. Williams established several standards for invoking adaptation and believed that it should be invoked only when necessary to explain the phenomenon at hand. When a flying fish leaps out of a wave and falls back into the water, for example, we do not have to invoke an adaptation for “getting back to water.” This behavior is explained more simply by the physical law of gravity.

adaptation is invoked not merely to explain the usefulness of a biological mechanism but to explain improbable usefulness (i.e., too precisely functional to have arisen by chance alone) (Pinker, 1997). Hypotheses about adaptations are, in essence, probability statements about why a reliable, efficient, and economic set of design features could not have arisen by chance alone

He asserted that sociobiology would “cannibalize psychology,” which of course was not greeted warmly by most psychologists. Further, he speculated that many cherished human phenomena, such as culture, religion, ethics, and even aesthetics, would ultimately be explained by the new synthesis.

Perhaps its very simplicity leads people to think that they can understand it completely a er only brief exposure to it—

Misunderstanding 1: Human Behavior Is Genetically Determined

Environmental input that triggers the development and activation of these adaptations. Consider calluses as an illustration.

Misunderstanding 2: If It’s Evolutionary, We Cannot Change It

In a similar manner, knowledge of our evolved social psychological adaptations along with the social inputs that activate them gives us power to alter social behavior, if that is the desired goal.

If anyfhing, knowledge unlocks control rather than blocks it

Misunderstanding 3: Current Mechanisms Are Optimally Designed

2. The New Science Of Evolutionary Psychology

Study that found that ovulating women initiate sexual encounters more than women at other phases of the cycle

Although evolution by natural selection is called a theory, its fundamental principles have been confirmed so many times—and never disconfirmed—that it is viewed by most biologists as a fact

The male pipefish seahorse receives the eggs from the female and then carries them around in his kangaroo-like pouch. These females compete aggressively with each other for the “best” males, and males in turn are choosy about who they mate with. This so-called sex-role-reversed species supports Trivers’s theory, showing that it is not “maleness” or “femaleness” itself that causes the sex difference in choosiness; rather, it is the relative parental investment of the two sexes.

Evolutionary hypotheses, when formulated precisely, are highly testable and eminently capable of being falsified when the evidence fails to support predictions derived from them (see Ketelaar & Ellis, 2000, for an excellent discussion of the issue of falsifiability).

The main point is not that the output of a psychological mechanism always leads to a successful solution but rather that the output of the mechanism on average tends to solve the adaptive problem better than competing strategies in the environments in which it evolved.

Although the mind could be divided in an infinite number of ways, most of them would be arbitrary. A powerful non-arbitrary analysis of the human mind is one that rests on function.

There is no such thing as a general adaptive problem (Symons, 1992). Because adaptive problems are specific, their solutions tend to be specific as well.

The carpenter gains flexibility not by having one “highly general tool” that can be used to cut, poke, saw, screw, twist, wrench, plane, balance, and hammer. Instead, the carpenter gains flexibility by having a large number of highly specific tools in the toolbox. These highly specific tools can then be used in many combinations that would not be possible with a single highly “flexible” tool. Indeed, it is difficult to imagine what a “general” tool would even look like, since there is no such thing as a “general carpenter’s problem.” Similarly, humans gain their flexibility from having a large number of complex, specific, functional psychological mechanisms.

Most of us holds that having a lot of innate mechanisms causes behavior to be inflexible. In fact, just the opposite is true. The more mechanisms we have, the greater the range of behaviors we can perform, and hence the greater the flexibility of our behavior.

The framework of evolutionary psychology dissolves dichotomies such as “nature versus nurture,” “innate versus learned,” and “biological versus cultural.” If you go back to the definition of evolved psychological mechanisms, you will note that (1) environments featuring recurrent selection pressure over deep time formed each mechanism; (2) environmental input during a person’s development is necessary for the emergence of each mechanism; and (3) environmental input is necessary for the activation of each mechanism. Thus, it does not make sense to ask whether a callus or jealous behavior is “evolved” or “learned.” “Evolved” is not the opposite of “learned.” All behavior requires evolved psychological mechanisms combined with environmental input at each stage in the causal chain.

labeling something as “learned” does not provide an explanation; it is simply a description that environmental input changes the organism in some way.

Learning requires evolved psychological adaptations.

Part 2: Problems Of Survival

3. Combating The Hostile Forces Of Nature

Both humans and rats have an adaptation called neophobia, defined as a strong aversion to new foods.

Children typically have to be coaxed by parents or others to try new foods, a manifestation of neophobia, indicating an important social element to human food consumption

The facial expression of disgust is universally recognized in all cultures; it is expressed by people who are blind from birth;

Interestingly, individuals who score high on a measure of pathogen disgust find relatively unattractive faces to be especially unattractive compared with people low on pathogen disgust (Park, van Leeuwen, & Stephan, 2012).

Mothers rate feces from their own infants as considerably less disgusting than feces from other infants, even when the feces samples were intentionally mislabeled (Case et al., 2006).

Profet (1992) hypothesizes that pregnancy sickness is an adaptation that prevents mothers from consuming and absorbing teratogens—toxins and other agents that might be harmful prenatally to her developing embryo.

The foods pregnant women find repugnant appear to correspond to those carrying the highest doses of toxins.

Women who do not have pregnancy sickness during the first trimester are roughly three times more likely to experience a spontaneous abortion than women who do experience such sickness

Profet’s analysis of pregnancy sickness highlights one of the benefits of adaptationist thinking. A phenomenon previously regarded as an illness instead may be an adaptation designed to combat a hostile force of nature—

Colon, a large, winding tube that is well designed for processing a vegetarian diet permeated with tough fiber.

The human body cannot produce vitamins A and B12, even though these are vital for human survival. Precisely these two vitamins are found in meat.

Provisioning hypothesis. Because meat is an economical and concentrated food resource, it can be transported effectively back to the home base to feed the young. In contrast, it is far less efficient to transport low-calorie food over long distances. Hunting thus provides a plausible explanation for the emergence of the heavy investment and provisioning that men channel toward their children.

Strong male coalitions, which appear to be characteristic of humans worldwide.

Humans seem to be unique among primates in showing extensive reciprocal relationships that can last years, decades, or a lifetime (Tooby & Devore, 1987). Meat from a large-game animal comes in quantities that far exceed what a single hunter and his immediate family could possibly consume. Furthermore, hunting success is highly variable;

In summary, although the provisioning of women and children is often hypothesized to be the primary adaptive explanation for the origins of hunting, the hunting hypothesis also can explain a host of other human phenomena. It can at least partially explain the emergence of strong coalitions among men, reciprocal alliance and social exchange among friends, the sexual division of labor, and the development of stone tools.

In short, the theory predicts that women will be better at “spatial location memory” as a gathering adaptation; men will be better at navigational abilities, map reading, and the sort of mental rotations that hurling a spear through space to take down an animal requires.

Spatial navigation abilities are used to solve adaptive problems other than gathering and hunting. They are also implicated in locating the sounds of a distressed child, migration from place to place among nomadic groups, one-on-one male fighting, and group-on-group warfare.

We love views and vistas and hate living in basements.

Fears are distinguished from phobias, which are fears that are wildly out of proportion to the realistic danger, are typically beyond voluntary control,

The developmental timing of the emergence of fears, in short, seems to correspond precisely to the onset of different adaptive problems—different forms of threat to survival. This illustrates the point that psychological mechanisms do not have to show up at birth to qualify as evolved adaptations. The onset of specific fears, like the onset of puberty, reflects developmentally timed adaptations.

They understood that after a lion kills a prey, the prey is no longer alive, can no longer eat, can no longer run, and that the dead state is permanent. This sophisticated understanding of death from encounters with predators develops by age 3 to 4.

It's the adults who then temper their fears of death with magic and stories

Those given the fever-reducing drug had more nasal stuffiness, a worse antibody response, and a slightly longer-lasting cold

Iron is food for bacteria. They thrive on it. Humans have evolved a means of starving these bacteria. When a person gets an infection, the body produces a chemical (leukocyte endogenous mediator) that reduces blood levels of iron. At the same time, the infected person spontaneously reduces the consumption of iron-rich food such as ham and eggs, and the human body reduces the absorption of whatever iron is consumed (Nesse & Williams, 1994). These natural bodily reactions essentially starve the bacteria, paving the way to combat the infection for a quick recovery. Although this information has been available since the 1970s, apparently few physicians and pharmacists know about it (Kluger, 1991). They continue to recommend iron supplements, which interfere with our evolved means for combating the hostile force of infections. Among the Masai tribe, fewer than 10 percent suffered infections caused by an amoeba. When a subgroup was given iron supplements, 88 percent of them developed infections (Weinberg, 1984). Somali nomads have naturally low levels of iron in their diets. When investigators sought to correct this with iron supplements, there was a 30 percent jump in infections within a month (Weinberg, 1984). Old people and women in America are routinely given iron supplements to combat “iron-poor blood,” which might paradoxically increase their rate of infections.

Part 5: Problems Of Group Living

10. Aggression And Warfare

Only two species have been documented to show male-initiated coordinated coalitions that raid neighboring territories and lethally attack members of their own species: chimpanzees and humans.

Aggression therefore can be used to defend against attack.

13. Toward A Unified Evolutionary Psychology

You don’t want to cling to the disciplinary divisions that strike you as somewhat arbitrary. Because evolution by selection is the only known process that is capable of generating complex functional organic design, evolutionary psychology appears to be the only viable metatheory that is powerful enough to integrate all these subdisciplines.

Traditional cognitive psychology is anchored by several core assumptions that evolutionary psychology challenges (Cosmides & Tooby, 1994). First, mainstream cognitive psychologists tend to assume that cognitive architecture is general purpose and content free.

Indeed, many cognitive psychologists have intentionally used artificial stimuli precisely because they want to get rid of the messy “content” with which subjects might have had prior experience. Literally hundreds of experiments were conducted using “nonsense syllables” to study memory processes because researchers believed that actual words with understandable content would “contaminate” the results. The use of artificial content-free stimuli makes sense if the mind is indeed a general-purpose information processor. It makes less sense if cognitive mechanisms are specialized to process information about particular tasks.

Tooby and Cosmides (1998) argue that an evolutionary perspective presents something of a paradox when contrasted with the view of humans as riddled with cognitive biases.

Tooby and Cosmides argue for an evolutionary theory of cognitive mechanisms called ecological rationality.

Debilitating or lethal consequences; cars are too evolutionarily recent. Problem-solving strategies, in short, might be exquisitely designed for solving one set of problems—those that recurred over evolutionary time—but very poor at solving artificial or novel problems like hazards posed by cars.

The criterion by which the “correctness” of solutions is evaluated is evolutionary: The decisions made by the cognitive mechanism led, on average, to better survival and enhanced reproduction in ancestral environments relative to alternative designs that were present at the time. What matters in the eyes of selection is not truth, validity, or logical consistency but simply what works in the currency of reproductive success. Before we conclude that human cognitive mechanisms are riddled with biases and errors of judgment, we need to ask which adaptive problems human cognitive mechanisms evolved to solve and what would be “sound judgment” or “successful reasoning” from an evolutionary perspective. If humans have trouble locating their cars by color at night in parking lots illuminated with sodium vapor lamps, we would not conclude that our visual system is riddled with errors. Our eyes were designed to perceive the color of objects under natural, not artificial, light (Shepard, 1992). Many of the research programs that have documented “biases” in judgment, it turns out, have used artificial, evolutionarily unprecedented experimental stimuli that are analogous to sodium vapor lamps.

These results suggest that people do not ignore base-rate information in making judgments, as long as the base-rate information is presented in a manner that maps more closely onto the sorts of input that humans would have been likely to process in ancestral times.

Conducting experiments that more closely mimic the formats of the information that humans were designed to process provides a different picture of the cognitive capabilities of humans when engaged in making judgments under uncertainty (see also Wang, 1996). The portrait of human cognitive mechanisms afforded by this line of thinking offers a marked contrast to the mainstream portrait of general mechanisms and crude heuristics. Rather than a single general intelligence, humans possess multiple intelligences. Rather than a general ability to reason, humans have many specialized abilities to reason, depending on the nature of the adaptive problems they were designed by selection to solve.

“That tribal chiefs are often both gifted orators and highly polygynous is a splendid prod to any imagination that cannot conceive of how linguistic skills could make a Darwinian difference”

Mainstream social psychology has amassed a number of important descriptions of empirical phenomena. It has not yet developed a powerful theory to explain the origins of these phenomena or shown how they fit within a larger understanding of human psychology. Evolutionary psychology provides the missing overarching theoretical framework.

Historical approaches to morality have been dominated by “rationalist” theories, whereby people arrive at a moral judgment through moral reasoning (Haidt, 2001, 2012). By logic and rationality, we are presumed to weigh the issues of right and wrong, harm and misdeed, justice and fairness, and arrive at the morally correct answer. Psychologist Jon Haidt has challenged this view, arguing instead that humans have evolved moral emotions that produce quick automatic evaluations. Only subsequently, when we are forced to explain or rationalize our moral stances, do we grasp for the straws of reasoning that we hope will support a judgment we’ve already made.

Haidt found similar reactions to a number of other scenarios that people find disagreeable but without a clear victim. A plausible explanation is that humans have evolved moral emotions. The repulsion of incest evolved to prevent inbreeding and becomes activated in reaction to the thought of sex between Julie and Mark

Transgressor, and found growth and fulfillment. They were most satisfied by endings in which the perpetrator of the injustice suffered greatly, knew that the suffering was retribution for the transgression, and experienced public humiliation in the process. In short, the moral outrage that people experience at cheating and violations of social contracts evolved to serve a policing function, holding others to their commitments and obligations.

Displays of shame might minimize attack or punishment from dominant others, lowering the costs to the violator of the moral code.

In sum, moral emotions might serve as “commitment devices” that promote prosocial deeds, reparation of harm, and punishment of cheaters, all while signaling to others that one is a good coalitional ally.

A father’s presence or absence early in a child’s life can calibrate the kind of sexual strategy he or she adopts later in life. Individuals growing up in fatherless homes during the first 5 to 7 years of life, according to this theory, develop the expectations that parental resources will not be reliably or predictably provided and that adult pair bonds will not be enduring. These individuals adopt a sexual strategy marked by early sexual maturation, early sexual initiation, and frequent partner switching—a strategy designed to produce a large number of offspring, with little investment in each.

Do attachment styles represent early environmental calibration, or do they reflect heritable individual differences, as suggested by some research (Bailey, Kirk, Zhu, Dunne, & Martin, 2000; Goldsmith & Harman, 1994)? Are individual differences in attachment stable over the life course? Do the underlying psychological mechanisms of attachment coordinate with the specific features of adaptive problems posed by each alternative strategy? These questions await further conceptual and empirical work. Nonetheless, studies demonstrate that early age of menarche is indeed linked with parental marital unhappiness and more rejection from the father, as well as with an earlier age of dating men. This suggests promise for the theory of early attachment in promoting different adult sexual strategies (Kim, Smith, & Palermiti, 1997), although it is not inconsistent with a pure heritability interpretation

Ultimately, a comprehensive evolutionary developmental psychology will include an account of the species-typical, sex-differentiated, and individually differentiated transformations over the life span of the adaptive problems faced, the differing environments that calibrate our evolved psychology.

As one niche becomes more crowded with competitors, success of those in the niche can suffer compared with those seeking alternative niches (Maynard Smith, 1982; Wilson, 1994). Selection favors mechanisms that cause individuals to seek niches in which the competition is less intense.

Like the red queen

In this example, the proclivity toward aggression is not directly heritable but rather would be “reactively heritable”—it is a secondary consequence of heritable body build that provides input into species-typical mechanisms of self-assessment and decision-making.

Evolved mechanisms are not only attuned to recurrent features of the external world, such as the reliability of parental provisioning, but can also be attuned to the evaluation of the self.

If facial features involved in appearing dominant and attractive are partially heritable, one can speculate that males have an evolved psychological mechanism designed to appraise the degree to which they appear dominant and attractive: “If high on these dimensions, pursue a short-term sexual strategy; if low, pursue a long-term mating strategy.” Stable individual differences in pursuing short-term and long-term sexual strategies, in this view, are not directly heritable. Instead, they represent adaptive individual differences based on the assessment of heritable information.

Linda Mealey (1995) proposed a theory of psychopathy based on frequency-dependent selection.

Psychopaths pursue a deceptive or “cheating” strategy in their social interactions, especially with interaction partners who are less attractive and those who they don’t expect to interact with in the future

In short, there are both benefits and costs to various personality traits, and selection can favor and maintain genetic diversity within the population.

Perceiving a dangerous animal behind a tree when one is not there and inferring sexual intentions when none exist are mistakes but might not be dysfunctional because, on average, the threshold for perceiving these phenomena led to greater survival and reproductive success than did alternative thresholds.

Although the experience of depression can be incredibly miserable, this emotional pain might serve adaptive functions. First, a depressed mood helps us to disengage from a hopeless strategy, conserve energy, use cognitive resources for focusing on complex social problems, and consequently motivate new paths to solving adaptive problems (Andrews & Thomson, 2009). Second, it deflates our “blind” human optimism, thus allowing us to more objectively reassess our goals (Nesse & Williams, 1994; Stevens & Price, 1996). Third, depression might function to send a needy signal to family, friends, or romantic partners that elicits investment, care, and helping from others—a “cry for help”

Although useful, the stress response is costly (excessive calorie use, tissue damage); therefore, there must be a reason why anxious responses occur so frequently. From an evolutionary perspective, the answer is clear: Of 100 potentially dangerous situations, one death is more costly than responding to 99 false alarms

If we mask these symptoms, we might thwart an otherwise natural healing process. This is analogous to treating a fever or a cough: These are mechanisms designed to help fix an infection or extrude foreign matter from the respiratory system.

Patterns of local within-group similarity and between-group differences are best regarded as phenomena that require explanation. Transforming these differences into an autonomous causal entity called “culture” confuses the phenomena that require explanation with a proper explanation of those phenomena. Attributing such phenomena to culture provides no more explanatory power than attributing them to God, consciousness, learning, socialization, or even evolution unless the causal processes that are subsumed by these labels are properly described.

Under high-variance conditions, there are tremendous benefits to sharing.

Although causality is often difficult to determine unambiguously, ecological variables such as parasite prevalence have been linked to cultural patterns—smaller ethnic groups, higher rates of polygyny, lower levels of parental care, and even greater cultural levels of “collectivism” (Nettle, 2009). Even cultural differences in proneness to shame, an emotion that motivates avoiding reputation-damaging action, can be explained in part by ecological variables such as cultural differences in mobility—the ability to move to other social groups (Sznycer et al., 2012).

(1) “Culture” is not an autonomous causal agent in competition with “biology” for explanatory power; (2) cultural diversities—local within-group similarities and between-group differences—are phenomena to be explained but do not, by themselves, provide an explanation for cultural phenomena; (3) cultural phenomena can be usefully divided into types, such as evoked culture and transmitted culture; (4) explanations for evoked culture require a foundation of evolved psychological mechanisms, without which the differently activated cultural diversity could not occur; and (5) transmitted culture also rests on a foundation of evolved psychological mechanisms that influence which ideas are attended to, encoded, retrieved from memory, and transmitted to other individuals. As evolutionists Pete Richardson and Rob Boyd conclude, “nothing about culture makes sense except in light of evolution”

So what are the cognitive adaptations of which religion is hypothesized to be a by-product? The first is our hyperactive agency detection device, which leads us to infer that unseen forces are human agents

Clouds and skies, of course, don’t have agency, yet we attribute human-like motivations to them as if they were agents with motives and intentions.

Theory of mind adaptations are extremely useful in predicting the behavior of other people, their proper function. It is a small extrapolation to go from “there are people watching me who have a desire for my well-being” to “there is an all-seeing god watching me who has a desire for my well-being.”

A 2-year-old reaching out to a mother to be soothed bears resemblance to a worshiper reaching out to a god: “we never lose the longing for a caretaker…

Others include costly signaling to gain entry to the group, emotionally arousing rituals that get culturally transmitted due to their attention-grabbing nature, and coalitional psychology to minimize within-group conflict

As humans became more and more reliant on cumulative culture, selection favored the ability to learn from and absorb complex cumulative culture and use it to their advantage. Thus, selection favored adaptations for cultural learning over individual learning. Rather than learning through individual trial and error, humans increasingly relied on the ability to observe others (e.g., prestigious peers, parents, teachers) and to imitate certain aspects of their behavior, even in early childhood (Legare, 2017). Humans also became cultural teachers—instructing others through verbal instruction or through modeling how to perform complex cultural tasks from basket weaving to computer coding

The display hypothesis appears to account for the age and sex distribution of culture production.

Just as artificial drugs can be created to “juice” our pleasure centers, art, music, and literature can “juice” psychological adaptations. Humans have learned to artificially activate existing mechanisms by inventing cultural products that mimic the stimuli for which the mechanisms were originally designed. These cultural activities, in short, are not adaptations but rather are non-adaptive by-products.

Studying human psychology through adaptive problems and their solutions—the organizing principle of this book—provides a more natural means of “cleaving nature at its joints” and hence crossing current disciplinary boundaries and unifying the field of psychology.

Like anatomy based on quadrants vs organs