Humans exhibit many of the same anatomical and physiological adaptations as other primates. When it comes topsychology and behavior, however, humans are much more complicated. Although we share with other primates basic emotions—rage, fear, sexual desire, and mother love—humans alone can communicate symbolically through written and spoken language, create and disseminate works of mathematics, science, and art, and manipulate the behavior of others with appeals to duty, religion, laws, and promises. And although other primates may be able to deceive one another, language allows us to devise elaborate stories, excuses, and lies. Evolutionary psychologists study the human mental functions that underlie these capacities by drawing on cross-species comparisons, cross-cultural comparisons, case studies (e.g., of brain damage), and laboratory experiments.
Like other evolutionary scientists, evolutionary psychologists generally assume that the attributes of the species they study (in this case, humans) have evolved through natural selection. Specifically, evolutionary psychologists assume that the brain circuitry and processes underlying human behavior include features maintained from our primate ancestry and modifications that were selected because, at the time they evolved, they led to adaptive behavior. It is thus sometimes said that the human brain houses an “adapted mind.” However, evolutionary psychologists do not assume that all human behavior is adaptive. Because the environments we live in today are in many ways dissimilar to the environments that our ancestors were designed to cope with, many of our behaviors may be anachronistic—once adaptive, but now neutral or even maladaptive. It is thus also sometimes said that the human brain houses a “mala-dapted mind.”
Physically, the human brain is much like that of all other mammals, consisting of a brain stem, which regulates mostly unconscious physical activity; a subcortical system, which modulates drives, emotions, physical sensations, and memory; and a convoluted cortex, which allows for the handling of greater amounts and complexity of information than is possible by members of other taxa. Primates as an order have brains relatively larger than other mammals of similar body sizes, and the human brain is significantly larger—even in proportion to body mass—than those of other primates. [See Brain Size Evolution.] As mammalian brains increased in size, the cerebral cortex increased relatively more than other parts. It is this expanded cortex that confers on humans great intelligence, a capacity for symbolic representation, and a reflective self-awareness.
Some parts of the human brain are physically distinguishable from adjacent areas, allowing for three-dimensional mapping of subcortical structures as well as two-dimensional mapping of the cortical surface. Boundaries of these structurally distinct areas often coincide with boundaries of functionally distinct areas, leading some theorists to conceive of the brain as not just a single organ, but as many organs or functional “modules” bundled together. These different organs or modules interconnect with one another to varying degrees, allowing both serial and parallel information processing at multiple levels of integration. Consequently, a person can engage in several activities at the same time, and can even experience two or more seemingly contradictory thoughts or feelings simultaneously—such as love and hate or curiosity and fear. Another consequence of this design is that, although some mental activity is available to consciousness, most occurs at a level of physical automaticity. We do not “know,” for example, how we change the focus of our eyes from near to far, or how we retrieve an old phone number out of memory, or how we come to distinguish and prefer chocolate as compared to vanilla—we just do.
Natural selection has responded to the existence of static and predictable stimuli with the evolution of simple low-level processing mechanisms. Collectively, these confer a set of panhuman “instinctive” behavioral responses and psychological preferences. The existence of spatially diverse and temporally dynamic stimuli, in contrast, has led to the evolution of more general and more complex learning mechanisms designed to generate what is statistically likely to be the most adaptive response in each unique or new circumstance. The expanded human cortex, with its increased capacity for associative learning, abstract generalization, and transitive reasoning, is what allows for this adaptive, functional plasticity, and is what underlies the great cultural and individual diversity of the human species.
The Adapted Mind
In stark contrast to Skinnerian behaviorists, who view the infant mind as a tabula rasa, or blank slate, evolutionary psychologists are quick to point out that baby brains are not, in fact, blank or empty; infants come into the world with rudimentary knowledge and specialized information processing systems already “wired in.” Furthermore, although knowledge does increase with experience, certain types of information are absorbed quite readily by the human brain, whereas other types are acquired only with difficulty. From an evolutionary perspective, the differential ease with which we learn about different aspects of our experience reflects their relative importance for our ancestors’ survival and reproductive success.
Perhaps the most important psychological adaptation for survival and reproduction is the sense of emotional attachment that develops between an infant and its mother. This is true for other primates as well as for humans, but humans develop motor skills more slowly as infants. Although we wean infants a bit earlier than chimpanzees do, human offspring require intensive investment and supervision long after weaning. Like other primates, young human children left on their own would have been vulnerable to starvation, exposure, predators, and the abuse of intolerant adults throughout evolutionary history. Close bonds between mother and child have thus been in the genetic interest of both mother and child—a bond to keep the child from wandering away from its primary protector and to keep the mother motivated to address the constant demands of what must often have been a distracting and irritating burden.
To this end, infants can recognize their mother’s voice and smell soon after birth, and as soon as their eyes are able to focus enough to discriminate individual faces, they can recognize—and show preference for—that of their own mother. Once human children are old enough to crawl (potentially into danger), babies develop an intense desire to be within sight of their mother, and when temporarily separated, they experience and communicate great distress. Mothers, reciprocally, develop an intense attachment to their child above all others, and they too experience distress upon separation. Attachment, separation anxiety, and the many forms of preverbal communication that mutually reward mother-infant interactions are features of the human psyche that have deep roots in our primate heritage and are both universal and compelling.
Other emotions appear early in life, across cultures, and without having to be learned. These so-called primary emotions include fear, anger, happiness, sadness, surprise, disgust and, according to some, curiosity. The primary emotions are universal not only in terms of our phenomenological experience but also in terms of their outward expression; facial expressions of the primary emotions are consistently performed across cultures and ages even in children blind from birth, and (among the sighted) are recognized quickly and reliably. Babies communicate with facial expression long before they can see the expressions of others, and at about seven months of age when their visual system has developed enough to discriminate facial detail, they are differentially and appropriately responsive to the facial expressions of those around them.
Later in development, children acquire the so-called social emotions, such as guilt, shame, allegiance, vengeance, sympathy, remorse, and gratitude. Unlike the primary emotions, the social emotions require an awareness and appreciation of social context, and so routinely appear only after a child is physically and mentally capable of navigating the social world—around ages four, five, and six. The social emotions are critical for cooperating with nonrelatives and for getting along in large social groups in which people must often depend upon one another. The social emotions motivate us to repeat and to reward mutually beneficial interactions, and to avoid and to punish those who take advantage.
Knowing whom to trust and whom to avoid requires the ability to discriminate between and remember unique individuals, as well as to remember how they behaved in previous encounters. To this end, natural selection has honed in us a rather amazing capacity to recognize individual faces and voices—even after as little as a single exposure and sometimes after as long as decades between encounters. Furthermore, recognition of specific individuals is often associated with an automatically generated emotion—fear, anger, pleasure, anxiety—depending on our past experience with that person. In fact, one of the first human universals to be documented was the facial expression of anxiety upon first seeing a stranger approach, followed by an “eyebrow flash” and a smile of relief and pleasure when he or she appeared close enough to be recognized as a friend.
We even have emotional responses to strangers who look or act like people we have previously met. These “gut feelings” about people (and situations) are, essentially, classically conditioned visceral responses that send us a message that if experience is anything to go by, we should pay special attention because these same conditions were, in our own past, associated with salient outcomes. Emotion, even in the form of such vague “intuitions,” is designed to guide us away from situations that are statistically likely to be harmful, and toward situations that are statistically likely to be beneficial. For evolutionary psychologists, the fact that our emotions and visceral responses are so automatic and so easily conditioned is a legacy of our past that has been built into our adapted brain and our adapted mind.
Important aspects of the behavior of the physical world also seem to be innately wired into, or easily acquired by, our adapted brain. Universally, babies appear to experience anxiety about steep drop-offs as soon as they can see them—without having to learn by experiencing a fall. They also flinch or move away from objects that are getting larger on a projection screen and therefore appear to be coming toward them. Although babies cannot count or do mathematics, they very quickly internalize the fundamental concepts of Newtonian mechanics (length, mass, speed, and gravity), as well as the concepts of more and less, larger and smaller. Without having to be taught, all but the most profoundly retarded of individuals automatically acquires, and communicates about, one of the most abstract concepts of all: the relation between past, present, and future.
Language is another kind of complex and abstract knowledge that is second nature to very young children. Across all cultures and language groups, children progress through a regularized series of stages of language development, acquiring the ability to both understand and produce grammatical speech (or, in the case of deaf children, visual signs). To acquire the 60,000-word vocabulary typical of an eighteen-year-old, a person must learn, on average, ten words a day; at their peak, children acquire several new words an hour. That this is a highly specialized kind of learning that is prewired into our adapted mind is evident by the fact that most adults have to work extremely hard to acquire a second or third language, and if they succeed in doing so, they are rarely as fluent as in their first language. Furthermore, it is exceedingly difficult to “teach” the smartest computers and robots how to understand even very elementary forms of speech, and although other animals can be taught the meanings of certain word or symbol sequences, they are unable to acquire the rules of grammar and syntax that come so naturally to human children. Linguistic skill is a human-specific attribute that develops easily and quickly during a critical period of brain development, and once achieved, it is never forgotten. For evolutionary psychologists, language facility is a paradigmatic feature of our adapted mind.
Another feature of our adapted mind is an innate preference for things that were “good” for our ancestors and a distaste of things that were “bad.” We naturally like sweet foods that provide us with the necessary glucose for our calorie-hungry brain and salty foods that provide us with the minerals to run our neuronal sodium pump; yet we have to acquire (and in some cases may never acquire) a taste for bitter foods and for foul-tasting or foul-smelling foods, which signal our brain that they may contain toxins. Even our taste for spices is adaptive: the most commonly used seasonings in cuisines around the world (lemon, garlic, various peppers, and oregano) are those that protect us with their potent antibacterial properties. Our brain also automatically causes us to develop highly ingrained aversions to foods that we ingested several hours before becoming ill. Even in cases when we consciously know that it was not the salad dressing or the broccoli au gratin that actually made us sick, we may still feel nauseous just thinking about the item ten years later. Our adapted mind is watching out for us—motivating us to eat things that we can use and to avoid things that might poison us.
Our adapted mind also demonstrates other kinds of “taste.” Children around the world show a decided preference for parklike landscapes that provide plenty of water, flowers, and foliage, and for forms of play that provide exercise, strengthen muscles, and increase physical coordination. Adults particularly admire the beautiful faces and shapely bodies of the young, healthy, and disease-free—those who are the safest to befriend and most profitable to mate with. And people of all ages have a predisposition to pay attention to, admire, and emulate the practices and preferences of successful peers. These aspects of our psychology are obvious to advertisers who today use outdoor scenes, sports, and sex to get our attention, and who pay movie stars and sporting idols to promote their products, but the reason they exist in the first place is because they helped our ancestors to survive, acquire physical and social skills, find a mate, reproduce, and successfully raise children.
Even our facility at logical reasoning—an aptitude that many philosophers consider to be the hallmark of our species and a measure of our mental flexibility— seems to be in some ways programmed. For example, just as we so readily develop emotional “intuitions” about certain kinds of people and places, we also readily develop mental stereotypes. Stereotypes are basically abstract concepts that arise from the mental integration of experience and that are designed to represent a statistically accurate synopsis of reality. Stereotypes are formed by a process that parallels what we call “inductive reasoning,” but which occurs at an automated rather than accessible level. The automaticity of stereotypes allows us to respond quickly to new stimuli so that we do not waste precious time assessing each nuance of each new minute of our day. In this way, having a mental stereotype is much like having the concept of “more versus less” or “sweet versus bitter”: it is a very gross assessment, but it is often all that is needed.
Deductive logic, too, exhibits features that signal the hand of natural selection. Solution of logic problems involving the classic “if p, then q” form may seem either simplistic or deviously difficult, depending on the specific content of the statements ρ and q. When problems are worded such that the task is to identify people who may be breaking a social rule (e.g., “If you take cake, then you must pay for it”), the solutions are readily apparent: anyone who takes cake (p) must be checked, and anyone who does not pay (not q) must be checked. When, however, problems are worded such that the task is to identify inanimate objects that may be breaking an arbitrary physical or numerical rule (e.g., “If a card is even-numbered, then it must go in a green folder”), the solutions prove to be quite elusive: everyone realizes that they must check for even-numbered cards (p), but a large majority fail to realize that they must check cards in the nongreen (not q) rather than the green (q) folders. That is, despite the identical format of the problems, success is achieved easily only on those that have clear relevance for human social interaction. Our facility for deductive logic is, like our memory and our emotional responsivity, selectively tuned to protect us from situations in which we might be harmed or cheated by other people.
In fact, it might have been the complexity of human social groups and interactions that created the selection pressures that led to our great intelligence. Populations of social species typically have some form of hierarchical organization involving complex, sometimes dynamic, relationships, and youngsters in such groups must learn not simply who is their mother, but who is their mother’s friend and who is their mother’s enemy, who leads the group and who follows, who dominates and who can be dominated. Furthermore, each individual’s status in the group must be continually monitored because relationships may change with age or reproductive status and as enmities and alliances form, dissolve, and reconfigure. Keeping track of all these identities, relationships, and their history requires keen faculties of discrimination, memory, and inference.
Although our highly social primate relatives can do these things to some extent, humans have taken this kind of mental social register to another level altogether. To be able to infer how other people might respond to a contemplated action, and thus to plan or strategize about our own behavior, we rely not only on our knowledge about particular others but also on a “theory of mind.” At about age four, children begin to understand that other people have independent thoughts, feelings, and beliefs—that each person has his or her own mind— and that the contents of each mind are, in fact, different. This critical insight completely changes how the child behaves, for now he or she can attempt to “manage” others by manipulating their feelings and beliefs. It is at this age that human children first start to show sympathy and empathy for others who are in distress, first start to use gifts, promises, and friendship to create alliances, and first start to lie to protect their own interests.
In many ways, our intelligence is really a specialized social intelligence. We devote much of our everyday conscious thought not to how to walk or focus our eyes or do science, but to figuring out how best to deal with others and how to improve our own image and status in their thoughts. We use our amazing gift for language not primarily to discuss philosophy or the structure of matter, but to gossip, seduce, insult, boast, and assign credit and blame. Our television, magazines, books, and newspapers cater to our hunger for knowledge about other people—even make-believe people—over that about other creatures or the physical world. In sum, just as coral polyps have evolved to be natural architects, sheep to be natural lawnmowers, and cats to be natural mousetraps, humans have evolved to be natural psychologists.
Because predicting other people’s behavior is so important to us, any aspect of a person that is consistent and can help us to predict accurately becomes salient. Such relatively stable behavioral predispositions are what we refer to in everyday parlance as “personality.” We care about others’ personality not only when it comes to important decisions about marriage, politics, and business partnerships, but also when making decisions about everyday social and economic transactions such as with whom to carpool or eat lunch. We have created an expansive lexicon describing intricate nuances of personality, both normal and abnormal, and we use these to label ourselves and others—sometimes for the sake of accurate prediction, and sometimes for more nefarious purposes.
There are many systems that modern psychologists use to discuss variation in personality, but from an evolutionary perspective there are two major dimensions that repeatedly emerge as most important: dominance/ submissiveness and friendliness/hostility. Our special attention to these two dimensions of personality seems to highlight once again the importance of social hierarchies, factions, and alliances to human life.
Also salient to us are some consistent differences between the sexes. Boys and men around the world are, on average, more physically aggressive, more competitive, more impulsive, and more risk-prone than girls and women, who are, on average, more nurturant, more empathetic, more cooperative, and more harm-avoidant than boys and men. These differences manifest in multitudinous ways, including differential representation of the sexes in certain activities and careers, greater participation by males in war and both violent and nonviolent crime, and a longer life expectancy for females with higher death rates for males at every age.
Although human politics and sex role relations are vastly more complicated than those of our primate (and other mammalian) kin, the physical and temperamental differences that underlie human sex differences are also found in other species. Male mammals generally have a higher metabolic rate than females, reach sexual maturity at a later age but at a larger size, are more aggressive, and have a greater ratio of muscle to fat than do females; like human males, they have a shorter life expectancy and higher death rates at all ages. Female mammals generally are more sexually discriminating than males, and in addition to being the sole provisioner of nursing young, are typically the sole social parent as well. These taxon-wide sex differences have evolved as a consequence of intrasexual competition among males and gestation-driven selection in females. Although we humans may exaggerate them or mask them with our cultural inventions, they are a fundamental aspect of our evolved nature.
The Maladapted Mind
Psychologists and psychiatrists are now beginning to apply evolutionary theory to human emotion, cognition, and personality to try to understand how our mental adaptations sometimes go awry in modern society, causing psychosocial dysfunction and pathology.
Of the primary emotions, the one that is most easily recognizable in pathological form is sadness. Clinical depression can become so severe as to culminate in suicide—clearly not an adaptive outcome. The symptoms of depression, however, can be seen to be extensions of normal sadness—an emotion that is designed to orient us away from misadventure after having experienced a loss. It is after having experienced a loss, of course, that further losses would be most costly. Thus, depression may serve as a protective buffer when we are at our weakest. The pathology of modern depression is not that it exists, but that we do not regroup and come out of it in a timely and functional manner. The selective process that finetuned our emotional responsivity could not have foreseen features of today’s existence such as the absence of extended kin support networks and the stress of constantly having to be alert to the behavior and intentions of strangers and modern “institutional entities” (e.g., law, big business, and the stock market). Our fears and anxieties are attuned to an era that is long gone: our (reasonable) fear of steep drop-offs can prevent us from flying, and our (reasonable) anxiety about strangers can give us disabling stage fright and contribute to xenophobia.
Reason itself can also be led astray. As heuristics, stereotypes are designed to work to our advantage, but the “experiences” that now go into our mental computations include not just real experiences that reflect true probabilities but also thousands upon thousands of images of murder and mayhem from movies, newspapers, and television. In fact, the more media a person consumes, the more likely he or she is to have exaggerated fears and inflated estimates of the likelihood of personally experiencing a frequently portrayed tragedy. Similarly, our judgments about our own physical attractiveness and the attractiveness of our partners is radically (negatively) altered by the fact that we are constantly surrounded by (artificially enhanced) images of the most beautiful of the beautiful.
Even personality attributes that may have been adaptive in the past may no longer be so. Aggressive and narcissistic men who are today diagnosed with antisocial personality disorder may have been the successful warrior-kings of old. Harm-avoidant and compulsive women who today succumb to anorexia may have been the best midwives and mothers.
Over a century ago, Charles Darwin predicted that “In the distant future … psychology will be based on a new foundation” (The Origin of Species, 1859). That time has come.
[See also Emotions and Self-Knowledge ; Human Families and Kin Groups ; Mate Choice , article on Human Mate Choice ;Parental Care ; Primates , article on Primate Societies and Social Life .]
Sources & References
Barkow, J., L. Cosmides, and J. Tooby, eds. The Adapted Mind. New York, 1992. A rather technical book that introduced the term evolutionary psychology and first defined this research program.
Baron-Cohen, S., ed. The Maladapted Mind. East Sussex, England, 1997. Each chapter discusses some form of modern psychopathology from an evolutionary perspective.
Buss, D. M. “Evolutionary Personality Psychology.” Annual Review of Psychology 42 (1991): 459–491.
Buss, D. M. “Evolutionary Psychology: A New Paradigm for Psychological Science.” Psychological Inquiry 6 (1995): 1–30. A paper on philosophy and method of evolutionary psychology, followed by peer commentaries and a rejoinder by the author.
Byrne, R. W., and A. Whiten. Machiavellian Intelligence: Social Expertise and the Evolution of Intellect in Monkeys, Apes, and Humans. Oxford, 1988.
Crawford, C, and D. L. Krebs, eds. Handbook of Evolutionary Psychology: Ideas, Issues, and Applications. Mahwah, N.J., 1998.
Cummins, D. D., and C. Allen, eds. The Evolution of Mind. Oxford, 1998.
Damasio, A. R. Descartes Error: Emotion, Reason and the Human Brain. New York, 1994. A premier neuroscientist discusses his compelling work on emotion and cognition.
Eibl-Eibesfeldt, I. Human Ethology. New York, 1989. A comprehensive and detailed documentary of human behavior in comparative perspective. Includes many classic photos and diagrams.
Frank, R. H. Passions within Reason: The Strategic Role of the Emotions. New York, 1988. An evolutionary economist shows how and why humans are not simply “rational” beings.
Gaulin, S. J. C, and D. H. McBurney. Psychology: An Evolutionary Approach. Upper Saddle River, N.J., 2001. An excellent textbook; the most reader-friendly item on this list.
Gazzaniga, M. S., ed. The Cognitive Neurosciences. Cambridge, Mass., 1995. This advanced specialty encyclopedia includes several entries on evolutionary psychology, including those by Premack and Premack (social awareness and theory of mind), Brothers (social awareness and theory of mind), Tooby and Cosmides (functional organization of the brain/mind), Cosmides and Tooby (cognition as mental computation), Gaulin (sex differences in cognition), Preuss (comparative cognitive neuroscience), Gallistel (cognitive modularity), and Daly and Wilson (parental motivations).
Griffiths, P. E. “Modularity, and the Psychoevolutionary Theory of Emotion.” Biology and Philosophy 5 (1990): 175–196.
Hrdy, S. Mother Nature: A History of Mothers, Infants, and Natural Selection. New York, 1999. A best-seller by a premier anthropologist focusing on human and nonhuman primate mother-infant interactions from an evolutionary perspective.
Irons, W. “How Did Morality Evolve?” Zygon: The Journal of Science and Religion, 26 (1991): 49–89.
Katz, L., ed. Evolutionary Origins of Morality: Cross-Disciplinary Perspectives. Essex, England, 2000. Four papers on the evolution of morality, each followed by a series of expert commentaries and a rejoinder by the author. Reprinted in its entirety from a special issue of the Journal of Consciousness Studies (7,1–2 2000).
Lamb, M. E., R. A. Thompson, W. P. Gardner, E. L. Charnov, and D. Estes. “Security of Infantile Attachment as Assessed in the ‘Strange Situation’: Its Study and Biological Interpretation.” Behavioral and Brain Sciences 7 (1984): 127–171. A technical review on attachment followed by a series of expert commentaries and a rejoinder by the authors.
MacDonald, K. B., ed. Sociobiological Perspectives on Human Development. New York, 1988. Includes chapters on adolescence as a life stage, development of cognition, and family interactions.
Mealey, L. Sex Differences: Developmental and Evolutionary Strategies. San Diego, Calif., 2000. Compares human and non-human behavioral and psychological sex differences from an evolutionary perspective.
Nesse, R. M. “Evolutionary Explanations of Emotions.” Human Nature 1 (1990): 261–289. A lucid presentation by an evolutionary psychiatrist; hard to find, but worth reading.
Panksepp, J. Affective Neuroscience. New York, 1998. Advanced text intergrating comparative neuroscience with theories of emotion.
Pinker, S. The Language Instinct. Cambridge, Mass., 1994. The best of the books on the evolution of language.
Scheibel, A. B., and J. W. Schopf, eds. The Origin and Evolution of Intelligence. Boston, 1997. Written at a somewhat less technical level than The Cognitive Neurosciences (above), this collection is also shorter and restricted to evolutionary angles, but authors and topics overlap. Includes Seyfarth and Cheney on monkey minds, Savage-Rumbaugh on ape language, Cosmides and Tooby on modularity, and Pinker on language.
Simpson, J. A., and D. T. Kenrick, eds. Evolutionary Social Psychology. Hillsdale, N.J., 1996. Many chapters discuss cognition in the context of social relationships.
Wilson, M., and M. Daly, “Competitiveness, Risk-taking, and Violence: The Young Male Syndrome.” Ethology and Sociobiology 6 (1985): 59–73. A classic discussion of male risk taking from an evolutionary perspective.