Evolutionary psychology is a social and natural science theoretical approach that examines psychological structure from a modern evolutionary perspective. It aims to determine which human psychological traits are evolved adaptations – that is, the functional products of natural or sexual selection in human evolution. In evolutionary biology, adaptationist thinking about physiological mechanisms such as the heart, lungs, and immune system is common. Some evolutionary psychologists argue that the modularity of the mind is similar to that of the body, with different modular adaptations serving different functions. According to these evolutionary psychologists, much of human behaviour is the result of psychological adaptations that evolved in response to recurring problems in human ancestral environments.
Evolutionary psychology is more than just a subfield of psychology; its evolutionary theory can provide a foundational, metatheoretical framework that integrates the entire field of psychology, just as evolutionary biology has done for biology.
Evolutionary psychologists believe that universally occurring behaviours or traits in all cultures are good candidates for evolutionary adaptations, such as the ability to infer others' emotions, distinguish kin from non-kin, identify and prefer healthier mates, and cooperate with others. Human social behaviour has been studied in terms of infanticide, intelligence, marriage patterns, promiscuity, perception of beauty, bride price, and parental investment. Evolutionary psychology's theories and findings have applications in a wide range of fields, including economics, the environment, health, law, management, psychiatry, politics, and literature.
Criticism of evolutionary psychology includes issues of testability, cognitive and evolutionary assumptions (such as modular brain functioning and large uncertainty about the ancestral environment), the importance of non-genetic and non-adaptive explanations, and political and ethical issues arising from research interpretations.
Human nature is viewed as the result of a universal set of evolved psychological adaptations to recurring problems in the ancestral environment, according to evolutionary psychology. Proponents argue that it seeks to integrate psychology into the other natural sciences by grounding it in biology's organising theory (evolutionary theory) and thus understanding psychology as a branch of biology.
According to anthropologist John Tooby and psychologist Leda Cosmides:
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.
The goal of evolutionary psychology is to identify evolved emotional and cognitive adaptations that represent "human psychological nature," just as human physiology and evolutionary physiology have worked to identify physical adaptations of the body that represent "human physiological nature." It is "not a single theory but a large set of hypotheses," according to Steven Pinker, and the term "has also come to refer to a particular way of applying evolutionary theory to the mind, with an emphasis on adaptation, genelevel selection, and modularity." The computational theory of mind underpins evolutionary psychology's understanding of the mind. It describes mental processes as computational operations, so a fear response, for example, is described as the result of a neurological computation that takes in perceptional data, such as a visual image of a spider, and outputs the appropriate reaction, such as fear of potentially dangerous animals. Because of the combinatorial explosion, any domain-general learning is impossible, according to this viewpoint. The domain is defined by Evolutionary Psychology as problems of survival and reproduction.
While philosophers have generally thought of the human mind as having broad faculties such as reason and lust, evolutionary psychologists describe evolved psychological mechanisms as being narrowly focused to deal with specific issues such as catching cheaters or choosing mates. The discipline considers the human brain to be made up of many functional mechanisms known as psychological adaptations, evolved cognitive mechanisms, or cognitive modules that have been designed by natural selection. Language-acquisition modules, incest-avoidance mechanisms, cheater-detection mechanisms, intelligence and sex-specific mating preferences, foraging mechanisms, alliance-tracking mechanisms, agent-detection mechanisms, and other mechanisms are examples. Some mechanisms, known as domain-specific, deal with recurring adaptive problems throughout human evolution. To deal with evolutionary novelty, domain-general mechanisms are proposed.
Evolutionary psychology derives from cognitive psychology and evolutionary biology, but it also incorporates behavioural ecology, artificial intelligence, genetics, ethology, anthropology, archaeology, biology, and zoology. It is closely related to sociobiology, but there are key differences between them, such as the emphasis on domain-specific rather than domain-general mechanisms, the importance of current fitness measures, the importance of mismatch theory, and psychology rather than behaviour.
The four categories of questions proposed by Nikolaas Tinbergen can aid in clarifying the distinctions between several distinct but complementary types of explanations. Traditional psychology focuses on the "how?" questions, whereas evolutionary psychology focuses on the "why?" questions.
Evolutionary psychology is founded on several core premises.
The brain is an information processing device that generates behaviour in response to both external and internal inputs.
Natural and sexual selection shaped the brain's adaptive mechanisms.
Throughout humanity's evolutionary history, different neural mechanisms have been specialised to solve problems.
The brain has evolved specialised neural mechanisms designed to solve problems that have recurred throughout deep evolutionary time, giving modern humans stone-age minds.
Most brain contents and processes are unconscious; and most mental problems that appear simple to solve are actually extremely difficult problems solved unconsciously by complex neural mechanisms.
Human psychology is made up of many specialised mechanisms, each of which is sensitive to different types of information or inputs. These mechanisms interact to produce visible behaviour.
The origins of evolutionary psychology can be traced back to Charles Darwin's theory of natural selection. Darwin predicted in The Origin of Species that psychology would develop an evolutionary basis:
In the distant future I see open fields for far more
important researches. Psychology will be based on a
new foundation, that of the necessary acquirement of
each mental power and capacity by gradation. — Darwin, Charles (1859). The Origin of Species
Two of his later books, The Descent of Man, and Selection in Relation to Sex in 1871 and The Expression of the Emotions in Man and Animals in 1872, were devoted to the study of animal emotions and psychology. William James' functionalist approach to psychology was inspired by Darwin's work. Darwin's theories of evolution, adaptation, and natural selection have shed light on why brains work the way they do.
The content of evolutionary psychology has been derived from the biological sciences (particularly evolutionary theory as it relates to ancient human environments, paleoanthropology, and animal behaviour) and the human sciences, particularly psychology.
W.D. Hamilton's (1964) papers on inclusive fitness, as well as Robert Trivers' (1972) theories on reciprocity and parental investment, aided in the establishment of evolutionary thinking in psychology and other social sciences. In his 1975 book Sociobiology: The New Synthesis, Edward O. Wilson combined evolutionary theory with studies of animal and social behaviour, building on the work of Lorenz and Tinbergen.
In the 1970s, two major branches of ethology emerged. To begin, the study of animal social behaviour (including humans) gave rise to sociobiology, which was defined in 1975 by its preeminent proponent Edward O. Wilson as "the systematic study of the biological basis of all social behaviour" and in 1978 as "the extension of population biology and evolutionary theory to social organisation." Second, there was behavioural ecology, which focused on the ecological and evolutionary basis of animal and human behaviour rather than social behaviour.
University departments began to include the term evolutionary biology in their titles in the 1970s and 1980s. Donald Symons' 1979 book The Evolution of Human Sexuality, as well as Leda Cosmides and John Tooby's 1992 book The Adapted Mind, helped usher in the modern era of evolutionary psychology. According to David Buller, the term "evolutionary psychology" is sometimes seen as denoting research based on the specific methodological and theoretical commitments of certain researchers from the Santa Barbara school (University of California), so some evolutionary psychologists prefer to call their work "human ecology," "human behavioural ecology," or "evolutionary anthropology."
The primary branches of psychology are developmental, social, and cognitive psychology. Establishing some measure of the relative influence of genetics and environment on behaviour has been central to behavioural genetics and its variants, particularly molecular studies that investigate the relationship between genes, neurotransmitters, and behaviour. Dual inheritance theory (DIT), which emerged in the late 1970s and early 1980s, takes a slightly different approach by attempting to explain how human behaviour is the result of two distinct and interacting evolutionary processes: genetic evolution and cultural evolution. Some see DIT as a "middle ground" between views emphasising human universals and those emphasising cultural variation.
The theories that underpin evolutionary psychology originated with Charles Darwin's work, including his speculations about the evolutionary origins of human social instincts. Modern evolutionary psychology, on the other hand, is only possible because of advances in evolutionary theory in the twentieth century.
According to evolutionary psychologists, natural selection has provided humans with many psychological adaptations in the same way that it has provided humans with anatomical and physiological adaptations. Psychological adaptations, like all adaptations, are said to be specialised for the environment in which an organism evolved, or the environment of evolutionary adaptedness. Sexual selection provides organisms with mating-related adaptations. [28 Sexual selection results in adaptations that help male mammals compete for females, despite the fact that they have a relatively high maximal potential reproduction rate. With a relatively low maximal potential reproduction rate for female mammals, sexual selection leads to choosiness, which aids females in selecting higher quality mates. Charles Darwin described both natural and sexual selection, and he used group selection to explain the evolution of altruistic (self-sacrificing) behaviour. However, group selection was deemed a weak explanation because in any group, the less altruistic individuals are more likely to survive, and the group as a whole becomes less self-sacrificing.
William D. Hamilton proposed inclusive fitness theory in 1964, emphasising a gene-centered approach to evolution. Hamilton observed that genes can help the survival and reproduction of other copies of the same genes (most simply, identical copies in the organism's close relatives) by influencing the organism's social traits in such a way that (statistically) results in helping the survival and reproduction of other copies of the same genes (most simply, identical copies in the organism's close relatives). Self-sacrificing behaviours (and the genes that influence them) can evolve if they help the organism's close relatives so much that it more than compensates for the individual animal's sacrifice, according to Hamilton's rule. The issue of how altruism can evolve was resolved by inclusive fitness theory.
Evolutionary psychology is informed by a number of mid-level evolutionary theories. According to the r/K selection theory, some species thrive by having a large number of offspring, whereas others thrive by having fewer offspring but investing significantly more in each one. The second strategy is used by humans. The theory of parental investment explains how parents invest more or less in individual offspring based on how successful those offspring are likely to be, and thus how much they may improve the parents' inclusive fitness. According to the Trivers–Willard hypothesis, parents in good circumstances tend to invest more in sons (who are best able to capitalise on good circumstances), whereas parents in bad circumstances tend to invest more in daughters (who are best able to have successful offspring even in poor conditions). Animals' life histories evolve to match their environments, determining details such as age at first reproduction and number of offspring, according to life history theory. According to dual inheritance theory, genes and human culture have interacted, with genes influencing cultural development and culture, in turn, influencing human evolution on a genetic level (see also the Baldwin effect).
Evolved psychological mechanisms
Evolutionary psychology is based on the hypothesis that cognition, like the hearts, lungs, livers, kidneys, and immune systems, has a functional structure with a genetic basis and thus evolved through natural selection. This functional structure, like other organs and tissues, should be universally shared by a species and should solve important problems of survival and reproduction.
Evolutionary psychologists seek to comprehend psychological mechanisms by comprehending the survival and reproductive functions that they may have served throughout evolutionary history. These may include the ability to deduce others' emotions, distinguish kin from non-kin, identify and prefer healthier mates, cooperate with others, and follow leaders. Evolutionary psychology sees humans as frequently in conflict with others, including mates and relatives, which is consistent with the theory of natural selection. For example, a mother may wish to wean her child from breastfeeding before her infant, allowing the mother to invest in additional children. The role of kin selection and reciprocity in the evolution of prosocial traits such as altruism is also recognised by evolutionary psychology. Humans, like chimps and bonobos, have subtle and adaptable social instincts that allow them to form extended families, lifelong friendships, and political alliances. Evolutionary psychologists have made modest findings in studies testing theoretical predictions on topics such as infanticide, intelligence, marriage patterns, promiscuity, perception of beauty, bride price, and parental investment.
Proponents of evolutionary psychology conducted some historical events explorations in the 1990s, but the response from historical experts was overwhelmingly negative, and little effort has been made to continue that line of research.
Historian Lynn Hunt says that the historians complained that the researchers:
have read the wrong studies, misinterpreted the results of experiments, or worse yet, turned to
neuroscience looking for a universalizing, anti-representational and anti-intentional ontology to
bolster their claims.
Hunt states that
"the few attempts to build up a subfield of psychohistory collapsed under the weight of its
presuppositions." She concludes that as of 2014 the "'iron curtain' between historians and
Products of evolution: adaptations, exaptations, byproducts, and random
Not all of an organism's characteristics are evolutionary adaptations. Traits can also be exaptations, byproducts of adaptations (also known as "spandrels"), or random variation between individuals, as shown in the table below.
Psychological adaptations are thought to be innate or relatively easy to learn and manifest in cultures all over the world. For example, toddlers' ability to learn a language with little or no training is most likely a psychological adaptation. On the other hand, because our ancestors did not read or write, learning to read and write today requires extensive training and is likely to involve the repurposing of cognitive capacities that evolved in response to selection pressures unrelated to written language. Variations in manifest behaviour, on the other hand, can result from universal mechanisms interacting with different local environments. Caucasians, for example, who relocate from a northern climate to the equator will have darker skin. The mechanisms that control their pigmentation do not change; instead, the input to those mechanisms changes, resulting in different outputs.
Obligate and facultative adaptations
The question of whether an adaptation is generally obligate (relatively robust in the face of typical environmental variation) or facultative may be raised (sensitive to typical environmental variation). The sweet taste of sugar and the pain of hitting one's knee against concrete are both the result of fairly obligate psychological adaptations; typical environmental variability during development has little effect on how they work. In comparison, facultative adaptations are similar to "if-then" statements. Adult attachment style, for example, appears to be particularly sensitive to early childhood experiences. The proclivity to form close, trusting bonds with others as adults is dependent on whether early childhood caregivers could be relied on to provide consistent assistance and attention. Another example of a facultative adaptation is the ability of skin to tan as a result of exposure to sunlight. When a psychological adaptation is facultative, evolutionary psychologists are interested in how developmental and environmental factors influence the adaptation's expression.
Evolutionary psychologists believe that behaviours or traits that occur universally across cultures are prime candidates for evolutionary adaptation. Language, cognition, social roles, gender roles, and technology are examples of cultural universals. Psychological adaptations that have evolved (such as the ability to learn a language) interact with cultural inputs to produce specific behaviours (e.g., the specific language learned).
Basic gender differences, such as men's greater eagerness for sex and women's greater coyness, are explained as sexually dimorphic psychological adaptations reflecting male and female reproductive strategies.
Evolutionary psychologists contrast their approach to the "standard social science model," which holds that the mind is a general-purpose cognition device shaped almost entirely by culture.
The environment of evolutionary adaptedness
According to evolutionary psychology, in order to properly understand brain functions, one must first understand the properties of the environment in which the brain evolved. That environment is known as the "environment of evolutionary adaptedness."
John Bowlby pioneered the concept of an evolutionary adapted environment as part of attachment theory. This is the environment to which a specific evolved mechanism has been adapted. The environment of evolutionary adaptedness is defined more specifically as the set of historically recurring selection pressures that formed a given adaptation, as well as those aspects of the environment that were required for the proper development and functioning of the adaptation.
Humans, or the genus Homo, first appeared between 1.5 and 2.5 million years ago, roughly coinciding with the start of the Pleistocene epoch 2.6 million years ago. Because the Pleistocene epoch ended only 12,000 years ago, most human adaptations either evolved during the Pleistocene or were maintained by stabilising selection. According to evolutionary psychology, the majority of human psychological mechanisms are adapted to reproductive problems that were common in Pleistocene environments. These issues encompass growth, development, differentiation, maintenance, mating, parenting, and social relationships in general.
The environment of evolutionary adaptation is vastly different from that of modern society. Modern humans' ancestors lived in smaller groups with more cohesive cultures and more stable and rich contexts for identity and meaning. Researchers look to existing hunter-gatherer societies for clues about how hunter-gatherers lived in an evolutionary adapted environment. Unfortunately, the few surviving hunter-gatherer societies differ from one another, and they have been pushed out of good land and into harsh environments, so it is unclear how closely they reflect ancestral culture. However, small-band hunter-gatherers all over the world provide a similar developmental system for the young ("hunter-gatherer childhood model," Konner, 2005; "evolved developmental niche" or "evolved nest;" Narvaez et al., 2013). The niche's characteristics are largely the same as those of social mammals, which evolved over 30 million years ago: soothing perinatal experience, several years of on-request breastfeeding, nearly constant affection or physical proximity, responsiveness to need (reducing offspring distress), selfdirected play, and, for humans, multiple responsive caregivers. Initial research indicates the importance of these components in early childhood for positive child outcomes.
Chimpanzees, bonobos, and other great apes are sometimes used by evolutionary psychologists to gain insight into human ancestors' behaviour.
Because an organism's adaptations were designed for its ancestral environment, a new and different environment can result in a mismatch. Because humans are primarily adapted to Pleistocene environments, psychological mechanisms occasionally exhibit "mismatches" to the modern environment. One example is that, despite the fact that guns kill approximately 10,000 people in the United States each year, while spiders and snakes kill only a handful, people learn to fear spiders and snakes about as easily as they do a pointed gun, and more easily than an unpointed gun, rabbits, or flowers. One possible explanation is that throughout the Pleistocene, spiders and snakes posed a threat to human ancestors, whereas guns (and rabbits and flowers) did not. As a result, there is a misalignment between humans' evolved fear-learning psychology and the modern environment.
This mismatch is also visible in the phenomenon of the supernormal stimulus, which elicits a stronger response than the stimulus for which the response evolved. Niko Tinbergen coined the term to refer to non-human animal behaviour, but psychologist Deirdre Barrett claims that supernormal stimulation governs human behaviour just as powerfully as it does that of other animals. She describes junk food as an exaggerated stimulus to cravings for salt, sugar, and fat, and she claims that television is an exaggeration of social cues such as laughter, smiling faces, and attention-grabbing action. Magazine centrefolds and double cheeseburgers trigger evolutionary adapted instincts for an environment where breast development was a sign of health, youth, and fertility in a prospective mate, and fat was a rare and vital nutrient. Mark van Vugt, a psychologist, recently argued that modern organisational leadership is a mismatch. His argument is that humans are not suited to working in large, anonymous bureaucracies with formal hierarchies. The human mind continues to respond to personalised, charismatic leadership in informal, egalitarian settings. As a result, many employees are dissatisfied and alienated. Salaries, bonuses, and other perks exploit instincts for relative status, which attracts men to senior executive positions in particular.