Evolutionary psychology (EP) attempts to explain mental and psychological traits—such as memory, perception, or language—as adaptations, that is, as the functional products of natural selection or sexual selection. Adaptationist thinking about physiological mechanisms, such as the heart, lungs, and immune system, is common in evolutionary biology. Evolutionary psychology applies the same thinking to psychology.
Evolutionary psychologists argue that much of human behavior is generated by psychological adaptations that evolved to solve recurrent problems in human ancestral environments. They hypothesize, for example, that humans have inherited special mental capacities for acquiring language, making it nearly automatic, while inheriting no capacity specifically for reading and writing. Other adaptations, according to EP, might include the abilities to infer others' emotions, to discern kin from non-kin, to identify and prefer healthier mates, to cooperate with others, and so on. Consistent with the theory of natural selection, evolutionary psychology sees organisms as often in conflict with others of their species, including mates and relatives. For example, mother mammals and their young offspring sometimes struggle over weaning, which benefits the mother more than the child. Humans, however, have a marked capacity for cooperation as well.
Evolutionary psychologists see those behaviors and emotions that are nearly universal, such as fear of spiders and snakes, as more likely to reflect evolved adaptations. Evolved psychological adaptations (such as the ability to learn a language) interact with cultural inputs to produce specific behaviors (e.g., the specific language learned). This view is contrary to the idea that human mental faculties are general-purpose learning mechanisms.
Evolutionary psychology (EP) is an approach to the entire discipline that views human nature as a universal set of evolved psychological adaptations to recurring problems in the ancestral environment. Proponents of EP suggest that it seeks to heal a fundamental division at the very heart of science --- that between the soft human social sciences and the hard natural sciences, and that the fact that human beings are living organisms demands that psychology be understood as a branch of biology. Anthropologist John Tooby and psychologist Leda Cosmides note:
"Evolutionary psychology is the long-forestalled scientific attempt to assemble out of the disjointed, fragmentary, and mutually contradictory human disciplines a single, logically integrated research framework for the psychological, social, and behavioral sciences—a framework that not only incorporates the evolutionary sciences on a full and equal basis, but that systematically works out all of the revisions in existing belief and research practice that such a synthesis requires.
Just as human physiology and evolutionary physiology have worked to identify physical adaptations of the body that represent "human physiological nature," the purpose of evolutionary psychology is to identify evolved emotional and cognitive adaptations that represent "human psychological nature." EP is, to quote Steven Pinker, "not a single theory but a large set of hypotheses" and a term which "has also come to refer to a particular way of applying evolutionary theory to the mind, with an emphasis on adaptation, gene-level selection, and modularity." EP proposes that the human brain comprises many functional mechanisms, called psychological adaptations or evolved cognitive mechanisms or cognitive modules designed by the process of natural selection. Examples include language acquisition modules, incest avoidance mechanisms, cheater detection mechanisms, intelligence and sex-specific mating preferences, foraging mechanisms, alliance-tracking mechanisms, agent detection mechanisms, and others. EP has roots in cognitive psychology and evolutionary biology (See also sociobiology). It also draws on behavioral ecology, artificial intelligence, genetics, ethology, anthropology, archaeology, biology, and zoology. EP is closely linked to sociobiology, but there are key differences between them including the emphasis on domain-specific rather than domain-general mechanisms, the relevance of measures of current fitness, the importance of mismatch theory, and psychology rather than behaviour. Many evolutionary psychologists, however, argue that the mind consists of both domain-specific and domain-general mechanisms, especially evolutionary developmental psychologists. Most sociobiological research is now conducted in the field of behavioral ecology.
The term evolutionary psychology was probably coined by American biologist Michael Ghiselin in a 1973 article published in the journal Science. Jerome Barkow, Leda Cosmides and John Tooby popularized the term "evolutionary psychology" in their highly influential 1992 book The Adapted Mind: Evolutionary Psychology and The Generation of Culture. EP has been applied to the study of many fields, including economics, aggression, law, psychiatry, politics, literature, and sex.
|How vs. Why Questions:||Sequential vs. Static Perspective|
Explanation of current form in terms of a historical sequence
Explanation of the current form of species
How organisms’ structures function
Developmental explanations for changes in individuals, from DNA to their current form
Mechanistic explanations for how an organism’s structures work
Why organisms evolved the structures (adaptations) they have
The history of the evolution of sequential changes in a species over many generations
A species trait that evolved to solve a reproductive or survival problem in the ancestral environment
The species-level categories (often called “ultimate explanations”) are
The individual-level categories are
Evolutionary psychology mostly focuses on the adaptation (functional) category.
Evolutionary psychology is a hybrid discipline that draws insights from modern evolutionary theory, biology, cognitive psychology, anthropology, economics, computer science, and paleoarchaeology. The discipline rests on a foundation of core premises. According to evolutionary psychologist David Buss, these include:
Evolutionary psychology is founded on the computational theory of mind, the theory that the mind, our "inner world," is the action of complex neural structures in the brain. For example, when a child shrinks in fear from a spider, the child's brain has attended to the spider, computed that it's a potential threat, and initiated a fear response.
Evolutionary psychology is rooted in evolutionary theory. It is sometimes seen not simply as a sub-discipline of psychology but as a way in which evolutionary theory can be used as a meta-theoretical framework within which to examine the entire field of psychology. A few biologists challenge the basic premises of evolutionary psychology.
Selection refers to the process by which environmental conditions "select" organisms with the appropriate traits to survive; these organisms will have such traits more strongly represented in the next generation. This is the basis of adaptive evolution. Darwin's great claim was that this "natural selection" was creative - it could lead to new traits and even new species, it was centred on individual survival, and it could explain the broad scale patterns of evolution.
Inclusive fitness theory, which was proposed by William D. Hamilton in 1964 as a revision to evolutionary theory, is basically a combination of natural selection, sexual selection, and kin selection. It refers to the sum of an individual's own reproductive success plus the effects the individual's actions have on the reproductive success of their genetic relatives. General evolutionary theory, in its modern form, is essentially inclusive fitness theory.
Inclusive fitness theory resolved the issue of how "altruism" evolved. The dominant, pre-Hamiltonian view was that altruism evolved via group selection: the notion that altruism evolved for the benefit of the group. The problem with this was that if one organism in a group incurred any fitness costs on itself for the benefit of others in the group, (i.e. acted "altruistically"), then that organism would reduce its own ability to survive and/or reproduce, therefore reducing its chances of passing on its altruistic traits. Furthermore, the organism that benefited from that altruistic act and only acted on behalf of its own fitness would increase its own chance of survival and/or reproduction, thus increasing its chances of passing on its "selfish" traits. Inclusive fitness resolved "the problem of altruism" by demonstrating that altruism can evolve via kin selection as expressed in Hamilton's rule:
| System level and problem|| Author|| Basic ideas|| Example adaptations|
| System Level:|
How to survive?
| Charles Darwin (1859)|| Natural Selection (or “survival selection”) The bodies and minds of organisms are made up of evolved adaptations designed to help the organism survive in a particular ecology (for example, the white fur of polar bears).|| Bones, skin, vision, pain perception, etc.|
| System Level: |
How to attract a mate and/or compete with members of one's own sex for access to the opposite sex?
| Charles Darwin (1859)|| Sexual selection Organisms can evolve physical and mental traits designed specifically to attract mates (e.g., the Peacock’s tail) or to compete with members of one’s own sex for access to the opposite sex (e.g., antlers).|
In most species with pronounced sexual selection, the adaptations are in males. These adaptations tend to evolve in species in which a successful male mates with multiple females. For instance, they appear in peacocks but not raptors, which are generally monogamous. Females rarely evolve such adaptations because being the "top female" doesn't improve a female's reproductive career as much as being "top male" improves a male's reproductive outcome.
| Peacock’s tail, antlers, courtship behavior, etc|
| System Level:|
Family & Kin
Problem: Gene replication. How to help those with whom we share genes survive and reproduce?
| W.D. Hamilton (1964)||Inclusive fitness (or a "gene’s eye view" of selection, "kin selection") / The evolution of sexual reproduction Selection occurs most robustly at the level of the gene, not the individual, group, or species. Reproductive success can thus be indirect, via shared genes in kin. Being altruistic toward kin can thus have genetic payoffs. (Also see Gene-centered view of evolution) Also, Hamilton argued that sexual reproduction evolved primarily as a defense against pathogens (bacteria & viruses) to "shuffle genes" to create greater diversity, especially immunological variability, in offspring.|| Altruism toward kin, parental investment, the behavior of the social insects with sterile workers (e.g., ants).|
| System Level:|
Non-kin small group
| Robert Trivers (1972)|| Parental Investment Theory / Parent - Offspring Conflict / Reproductive Value The two sexes often have conflicting strategies regarding how much to invest in offspring, and how many offspring to have.|
Parents allocate more resources to their offspring with higher reproductive value (e.g., "mom always liked you best"). Parents and offspring may have conflicting interests (e.g., when to wean, allocation of resources among offspring, etc.).
| Sexually dimorphic adaptations that result in a "battle of the sexes," parental favoritism, timing of reproduction, parent-offspring conflict, sibling rivalry, etc.|
| System Level: Non-kin small group
How to succeed in competitive interactions with non-kin? How to select the best strategy given the strategies being used by competitors?
| John von Neumann and Oskar Morgenstern (1944);|
John Maynard Smith (1982)
Game Theory / Evolutionary Game Theory
Organisms adapt, or respond, to competitors depending on the strategies used by competitors. Strategies are evaluated by the probable payoffs of alternatives. In a population, this typically results in an "evolutionary stable strategy," or "evolutionary stable equilibrium" -- strategies that, on average, cannot be bettered by alternative strategies.
| Facultative, or frequency-dependent, adaptations. Examples: hawks vs. doves, cooperate vs. defect, fast vs. coy courtship, etc.|
| System Level: Non-kin small group
How to maintain mutually beneficial relationships with non-kin in repeated interactions?
| Robert Trivers (1971)||"Tit for Tat" Reciprocity One can play nice with non-kin if a mutually beneficially reciprocal relationship is maintained across multiple social interactions, and cheating is punished.||Cheater detection, emotions of revenge and guilt, etc.|
| System Level: Non-kin, large groups governed by rules and laws|
How to maintain mutually beneficial relationships with strangers with whom one may interact only once?
| Herbert Gintis (2000, 2003); and others.|| Generalized Reciprocity (Also called "strong reciprocity"). One can play nice with non-kin strangers even in single interactions if social rules against cheating are maintained by neutral third parties (e.g., other individuals, governments, institutions, etc.), a majority group members cooperate by generally adhering to social rules, and social interactions create a positive sum game (i.e., a bigger overall "pie" results from group cooperation).|
Generalized reciprocity may be a set of adaptations that were designed for small in-group cohesion during times of high inter-tribal warfare with out-groups.
Today the capacity to be altruistic to in-group strangers may result from a serendipitous generalization (or "mismatch") between ancestral tribal living in small groups and today's large societies that entail many single interactions with anonymous strangers. (The dark side of generalized reciprocity may be that these adaptations may also underlie aggression toward out-groups.)
| To in-group members: Capacity for generalized altruism, acting like a "good Samaritan," cognitive concepts of justice, ethics and human rights.|
To out-group members:
Capacity for xenophobia, racism, warfare, genocide.
| System Level: Large groups / culture.
How to transfer information across distance and time?
| Richard Dawkins (1976)||Memetic Selection Genes are not the only replicators subject to evolutionary change. “Memes” (e.g., ideas, rituals, tunes, cultural fads, etc.) can replicate and spread from brain to brain, and many of the same evolutionary principles that apply to genes apply to memes as well. Genes and memes may at times co-evolve ("gene-culture co-evolution").|| Language, music, evoked culture, etc. Some possible by-products, or "exaptations," of language may include writing, reading, mathematics, etc.|
Additional middle-level evolutionary theories used in EP include:
While philosophers have generally considered human mind to include broad faculties, such as reason and lust, evolutionary psychologists describe EPMs as narrowly evolved to deal with specific issues, such as catching cheaters or choosing mates.
Some mechanisms, termed domain-specific, deal with recurrent adaptive problems over the course of human evolutionary history. Domain-general mechanisms, on the other hand, deal with evolutionary novelty.
EP argues that to properly understand the functions of the brain, one must understand the properties of the environment in which the brain evolved. That environment is often referred to as the environment of evolutionary adaptedness, or EEA for short.
The term environment of evolutionary adaptedness was coined by John Bowlby as part of attachment theory. It refers to the environment to which a particular evolved mechanism is adapted. More specifically, the EEA is defined as the set of historically recurring selection pressures that formed a given adaptation, as well as those aspects of the environment that were necessary for the proper development and functioning of the adaptation. In the environment in which ducks evolved, for example, attachment of ducklings to their mother had great survival value for the ducklings. Because the first moving being that a duckling was likely to see was its mother, a psychological mechanism that evolved to form an attachment to the first moving being would therefore properly function to form an attachment to the mother. In novel environments, however, the mechanism can malfunction by forming an attachment to a dog or human instead.
Evolutionary psychologists use several methods and data sources to test their hypotheses, as well as various comparative methods to test for similarities and differences between: humans and other species, males and females, individuals within a species, and between the same individuals in different contexts. They also use more traditional experimental methods involving, for example, dependent and independent variables.
Evolutionary psychologists also use various sources of data for testing, including archeological records, data from hunter-gather societies, observational studies, self-reports, public records, and human products.
Areas of research in evolutionary psychology can be divided into broad categories of adaptive problems that arise from the broader theory of evolution itself: survival, mating, parenting, kinship, and group living.
Given that sexual reproduction is the means by which genes are propagated into future generations, sexual selection plays a large role in the direction of human evolution. Human mating, then, is of interest to evolutionary psychologists who aim to investigate evolved mechanisms to attract and secure mates. Several lines of research have stemmed from this interest, such as studies of mate selection, mate poaching , and mate retention , to name a few.
Much of the research on human mating is based on parental investment theory , which makes important predictions about the different strategies men and women will use in the mating domain (see above under "Middle-level evolutionary theories"). In essence, it predicts that women will be more selective when choosing mates, whereas men will not, especially under short-term mating conditions. This has led some researchers to predict sex differences in such domains as sexual jealousy (however, see also, ), wherein females will react more aversively to emotional infidelity and males will react more aversively to sexual infidelity. This particular pattern is predicted because the costs involved in mating for each sex are distinct. Women, on average, should prefer a mate who can offer some kind of resources (e.g., financial, commitment), which means that a woman would also be more at risk for losing those valued traits in a mate who commits an emotional infidelity. Men, on the other hand, are limited by the fact that they can never be certain of their paternity because they do not bear offspring themselves. This obstacle entails that sexual infidelity would be more costly for a man because it is not in his best interest to invest resources in another man's offspring.
Another interesting line of research is that which examines women's mate preferences across the ovulatory cycle . The theoretical underpinning of this research is that ancestral women would have evolved mechanisms to select mates with certain traits depending on their hormonal status. For example, the theory hypothesizes that, during the ovulatory phase of a woman's cycle (approximately days 10-15 of a woman's cycle ), a woman who mated with a male with high genetic quality would have been more likely, on average, to produce and rear a healthy offspring than a woman who mated with a male with low genetic quality. These putative preferences are predicted to be especially apparent for short-term mating domains because a potential male mate would only be offering genes to a potential offspring. This hypothesis allows researchers to examine whether women select mates who have characteristics that indicate high genetic quality during the high fertility phase of their ovulatory cycles. Indeed, studies have shown that women's preferences vary across the ovulatory cycle. In particular, Haselton and Miller (2006) showed that highly fertile women prefer creative but poor men as short-term mates. Creativity may be a proxy for good genes . Research by Gangestad et al. (2004) indicates that highly fertile women prefer men who display social presence and intrasexual competition; these traits may act as cues that would help women predict which men may have, or would be able to acquire, resources.