Evolutionary psychology

Evolutionary psychology (abbreviated ev-psych or EP) is a theoretical approach to psychology that attempts to explain useful mental and psychological traits—such as memory, perception, or language—as adaptations, i.e., as the functional products of natural selection. The purpose of this approach is to bring the functional way of thinking about biological mechanisms such as the immune system into the field of psychology, and to approach psychological mechanisms in a similar way. In short, evolutionary psychology is focused on how evolution has shaped the mind. Though applicable to any organism with a nervous system, most research in evolutionary psychology focuses on humans.

Overview

Evolutionary Psychology 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." Evolutionary Psychology proposes that the human brain comprises many functional mechanisms, called psychological adaptations or evolved cognitive mechanisms 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 so on. Evolutionary psychology has roots in cognitive psychology and evolutionary biology. It also draws on behavioral ecology, artificial intelligence, genetics, ethology, anthropology, archaeology, biology, and zoology. Evolutionary psychology 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 Michael Ghiselin in his 1973 article in Science. Jerome Barkow, Leda Cosmides and John Tooby popularized the term in their highly influential 1992 book The Adapted Mind: Evolutionary Psychology and The Generation of Culture. Evolutionary psychology has been applied to the study of many fields, including economics, aggression, law, psychiatry, politics, literature, and sex.

Evolutionary psychology uses Nikolaas Tinbergen's four categories of questions and explanations of animal behavior. Two categories are at the species level; two, at the individual level. The species-level categories (often called “ultimate explanations”) are

• the function (i.e., adaptation) that a behavior serves and
• the evolutionary process (i.e., phylogeny) that resulted in this functionality.

The individual-level categories are

• the development of the individual (i.e., ontogeny) and
• the proximate mechanism (e.g., brain anatomy and hormones).

Evolutionary psychology emphasizes the functionality category.

General evolutionary theory

Main article: Evolution

The idea that organisms are composed of a number of parts that serve different functions (i.e., living things are, in some sense, machines) goes back at least to Aristotle. This idea is the foundation of modern medicine and biology. William Paley, drawing upon the work of many others, argued that organisms are machines designed to function in particular environments. Paley believed that this evidence of 'design' was evidence for a designer—God. Charles Darwin appears to have been impressed with Paley's argument that organisms are designed for particular environments. The theory of natural selection, created by Charles Darwin and Alfred Russel Wallace, provided a scientific account of the origins of functional design in the natural world that did not invoke a supernatural designer.

Evolutionary psychology is ultimately rooted in the basic theoretical principles of 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.^{[citation needed]}

Natural selection, a key component of evolutionary theory, involves three main ingredients:

• Variation refers to a state in which there exists a variety of genetically determined traits within a population.
• Heritability refers to genetically determined traits which vary in their expression within a population (hair color, intelligence, height, anxiety-level, etc.)
• Selection refers to those heritable traits that remain in, and spread through, a population because those traits increased the reproduction of the organism.

Many traits that are selected for can actually hinder survival of the organism while increasing its reproductive opportunities. Consider the classic example of the peacock's tail. It is metabolically costly, cumbersome, and essentially a "predator magnet." What the peacock's tail does do is attract mates. Thus, the type of selective process that is involved here is what Darwin called sexual selection." Sexual selection can be divided into two types:

• Intersexual selection, which refers to the traits that one sex generally prefers in the other sex, (e.g. the peacock's tail).
• Intrasexual competition, which refers to the competition among members of the same sex for mating access to the opposite sex, (e.g. two stags locking antlers).

Darwin and Wallace proposed that natural and sexual selection, and not a supernatural designer, explain why organisms comprise a number of functional mechanisms that often exhibit surprisingly complex evidence of design. This theory has two important implications for the nature of these mechanisms, including the mechanisms of the brain. First, all evolved mechanisms must serve some function that ultimately increased the reproduction of the organism. Second, the design of each mechanism will be best understood in relation to the environment in which it evolved.

Inclusive fitness

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:

cost < relatedness × benefit

In other words, altruism can evolve as long as the fitness cost of the altruistic act on the part of the actor is less than the degree of genetic relatedness of the recipient times the fitness benefit to that recipient. This perspective reflects what is referred to as the gene-centered view of evolution and demonstrates that group selection is a very weak selective force. However, in recent years group selection has been making a comeback, (albeit a controversial one), as multilevel selection, which posits that evolution can act on many levels of functional organization, (including the "group" level), and not just the "gene" level.

Middle-level evolutionary theories

Middle-level evolutionary theories are theories that encompass broad domains of functioning. They are compatible with general evolutionary theory but not derived from it. Furthermore, they are applicable across species. During the early 1970's, three very important middle-level evolutionary theories were contributed by Robert Trivers:

• The theory of reciprocal altruism explains how altruism can arise amongst non-kin, as long as there is a sufficient probability of the recipient of the altruistic act reciprocating at a later date. The possibility was also noted by Trivers, later coined 'indirect altruism' by Richard Alexander, that reciprocation could be provided by third parties, raising the issue of social reputation.

• Parental investment theory refers to the different levels of investment in offspring on the part of each sex. For example, females in any species are defined as the sex with the larger gamete. In humans, females produce approximately one large, metabolically costly egg per month, as opposed to the millions of relatively tiny and metabolically cheap sperm that are produced each day by males. Females are fertile for only a few days each month, while males are fertile every day of the month. Females also have a nine month gestation period, followed by a few years of lactation. Males' obligatory biological investment can be achieved with one copulatory act. Consequently, human females have a significantly higher obligatory investment in offspring than males do. (In some species, the opposite is true.) Because of this difference in parental investment between males and females, the sexes face different adaptive problems in the domains of mating and parenting. Therefore, it is predicted that the higher investing sex will be more selective in mating, and the lesser investing sex will be more competitive for access to mates. Thus, differences in behaviour between sexes is predicted to exist not because of maleness or femaleness per se, but because of different levels of parental investment.

• The theory of parent-offspring conflict rests on the fact that even though a parent and his/her offspring are 50% genetically related, they are also 50% genetically different. All things being equal, a parent would want to allocate their resources equally amongst their offspring, while each offspring may want a little more for themselves. Furthermore, an offspring may want a little more resources from the parent than the parent is willing to give. In essence, parent-offspring conflict refers to a conflict of adaptive interests between parent and offspring.

However, if all things are not equal, a parent may engage in discriminative investment towards one sex or the other, depending on the parent's condition. Recall that females are the heavier parental investors in our species. Because of that, females have a better chance of reproducing at least once in comparison to males. Thus, according to the Trivers-Willard hypothesis, parents in good condition are predicted to favor investment in sons, and parents in poor condition are predicted to favor investment in daughters.

Products of the evolutionary process

All biological traits are products of the evolutionary process. Adaptationist methods, including evolutionary psychology, attempt to distinguish between adaptations and traits produced as by-products of adaptation.

• Adaptations are specially designed, species-typical traits that, (in terms of fitness costs), are "cost-efficient" and function to solve problems related to one's inclusive fitness. An example would be the Giant Panda's so-called 'thumb'.

• Evolutionary by-products are traits that were not specially designed for an adaptive function, although they may also be species-typical and may also confer benefits on the organism. A "spandrel" is a term coined by S.J.Gould and R.Lewontin (1979a) for traits which confer no adaptive advantage to an organism, but are 'carried along' by an adaptive trait. Their example being the lengthening of a bone in the hind limb of the Giant Panda, as a result of the lengthening of the corresponding bone in the forelimb. The bone in the forelimb has adapted to perform a function similar to that of an opposable thumb. The change in the hind limb, arguably, confers no adaptive advantage, whereas the change in the forelimb certainly does. The important implication of this idea for Evolutionary Psychology being, that therefore not every trait can be accounted for in terms of adaptive advantage. For instance, Gould puts forward the hypothesis that language itself in humans came about as a spandrel: "Natural selection made the human brain big, but most of our mental properties and potentials may be spandrels - that is, nonadaptive side consequences of building a device with such structural complexity" (S.J.Gould. The Pleasures of Pluralism , p.11) But of course, once a trait confers an adaptive advantage, as arguably most of our "mental properties and potentials" do, it is no longer a spandrel, and thus opens the debate concerning the importance of the concept of spandrels.

Natural selection is not the only evolutionary process that can change gene frequencies and produce novel traits. Genetic drift, or noise, refers to random effects resulting from chance variation in the genes, environment, or development. An example would be dry earwax in humans. Unlike natural selection, genetic drift does not produce complex, functionally designed adaptations.

Evolved psychological mechanisms: the core of evolutionary psychology

Main article: Evolved psychological mechanisms

Evolutionary psychology is based on the belief that, just like hearts, lungs, livers, kidneys, and immune systems, cognition has functional structure that has a genetic basis, and therefore has evolved by natural selection. Like other organs and tissues, this functional structure should be universally shared amongst a species, and should solve important problems of survival and reproduction. Evolutionary psychologists seek to understand psychological mechanisms by understanding the survival and reproductive functions they might have served over the course of evolutionary history.

Evolutionary psychologists subdivide the concept of psychological mechanisms into two general categories:

• Domain-specific mechanisms, which deal with recurrent adaptive problems over the course of human evolutionary history
• Domain-general mechanisms, which deal with evolutionary novelty

The environment of evolutionary adaptedness

The term environment of evolutionary adaptedness, often abbreviated EEA, 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.

The genus Homo, which includes modern humans, appeared between 1.5 and 2.5 million years ago, a time that roughly coincides with the start of the Pleistocene 1.8 million years ago. Because the Pleistocene ended a mere 12,000 years ago, most human adaptations either newly evolved during the Pleistocene, or were maintained by stabilizing selection during the Pleistocene. Evolutionary psychology therefore proposes that the majority of human psychological mechanisms are adapted to reproductive problems frequently encountered in Pleistocene environments. In broad terms, these problems include those of growth, development, differentiation, maintenance, mating, parenting, and social relationships. To properly understand human mating psychology, for example, it is essential to recognize that in the EEA (as now) women got pregnant and men did not.

If humans are mostly adapted to Pleistocene environments, then some psychological mechanisms should occasionally exhibit “mismatches” to the modern environment, similar to the attachment patterns of ducks. One example is the fact that although about 30,000 people are killed with guns in the US annually (CDC pdf), whereas spiders and snakes kill only a handful, people nonetheless 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 (Öhman and Mineka 2001). A potential explanation is that spiders and snakes were a threat to human ancestors throughout the Pleistocene, whereas guns, rabbits and flowers were not. There is thus a mismatch between our evolved fear learning psychology and the modern environment.

In sum, evolutionary psychology argues that to properly understand the functions of the brain one must understand the properties of the environment in which the brain evolved.

Controversies

Animal behavior studies have long recognized the role of evolution; the application of evolutionary theory to human psychology, however, is controversial. There are many families of criticism of the idea.

How knowable is the early environment (Environment of Evolutionary Adaptedness)?

Some critics of evolutionary psychology claim that because little is known about the Pleistocene, the evolutionary context in which humans developed (including population size, structure, lifestyle, eating habits, habitat, and more), there is little basis on which evolutionary psychology may operate. Most EP research is thus confined to certainties about the past, such as pregnancies only occurring in women, and that humans lived in groups.

Many evolutionary psychologists argue that this criticism is based on a misunderstanding. Evolutionary psychologists argue that they use knowledge of the environment of evolutionary adaptedness to generate hypotheses regarding possible psychological adaptations, and subsequently, these hypotheses can be tested and evaluated against the empirical evidence in just the same way that any other hypothesis generated from any other theoretical perspective can be assessed.

Furthermore, evolutionary psychologists posit that there are many environmental features that we can be sure played a part in our species' evolutionary history. They argue that our hunter-gatherer ancestors most certainly dealt with predators and prey, food acquisition and sharing, mate choice, child rearing, interpersonal aggression, interpersonal assistance, diseases and a host of other fairly predictable challenges that constituted significant selection pressures.^[1]

There also exists debate within evolutionary psychology about the nature of the EEA. Many evolutionary psychologists contend that many aspects of the EEA were not as consistent as other evolutionary psychologists would argue. This argument is used to support the notion that the mind consists of not only domain-specific psychological mechanisms but of domain-general ones as well, that deal with environmental novelty.

Too many alternative hypotheses

Critics claim that many valid hypotheses, including contradictory ones, can be drawn from the same evolutionary principles. Evolutionary psychology can predict many, or even all, behaviours for a given situation, including contradictory ones. Therefore many human behaviours will always fit some hypotheses. The central paradigm of evolutionary psychology is impossible to prove, and the predicting power of evolutionary psychology is doubtful. For example, kin selection predicts that humans will be altruistic toward relatives in proportion to their relatedness, while reciprocal altruism predicts that we will be altruistic toward people from whom we can expect altruism in the future (not strangers). However, altruism towards a complete stranger fits the handicap principle. Thus altruism toward every class of person fits some well-known hypothesis. This doesn't seem to give us any way to predict how a human will act in a given situation.

Evolutionary psychologists respond that their discipline is not primarily concerned with explaining the behavior of specific individuals, but rather broad categories of human behaviors across societies and cultures. It is the search for species-wide trends in behavior that distinguishes evolutionary psychology from cultural or social explanations.

Falsifiability

Critics claim that many of the propositions of evolutionary psychology are not falsifiable. It is not possible to conduct definitive experiments on humans on an evolutionary timescale. This criticism in particular is common and often refers to evolutionary psychological theories as just-so stories.

The methods that evolutionary psychologists actually use for testing include comparing different species, comparing males and females, comparing individuals within a species and comparing the same individuals in different contexts. Their sources of data for testing evolutionary hypotheses include archeological records, data from hunter-gatherer societies, observations, self-reports, life-history data and public records, and human products. Source: Evolutionary Psychology: The New Science of the Mind by David Buss.

Biology versus environment

Some studies have been criticized for their tendency to attribute to evolutionary processes elements of human cognition that may be attributable to social processes (e.g. preference for particular physical features in mates).

Evolutionary psychologists respond that many traits have been shown to be universal in humans and that social processes are related to evolutionary processes. They argue that statements such as "biology vs. environment" and "genes vs. culture" amount to false dichotomies. Evolutionary psychologists justify this claim by arguing that behavior results from an organism interacting with its environment. Psychological mechanisms, they argue, are created by genes, (which, in turn, were selected for by the evolutionary process), and those mechanisms help the organism negotiate its environment. Furthermore, they assert that many aspects of the environment, (e.g. culture and social institutions), are rested upon those mechanisms. In short, evolutionary psychologists argue that there is a bidirectional influence between things like "biology and environment" and "cognition and social processes."

Reductionism

Evolutionary Psychology is grounded on the theory that fundamentally our psychology is based on biology, the composition of our brains. This is a form of reductionism, a research philosophy according to which the nature of complex things can be understood in terms of simpler or more fundamental things (i.e. reduced). Importantly, reductionism as applied to consciousness and the brain, comes in various forms, some of which may be more philosophically problematic for Evolutionary Psychology than others. It is a long-standing matter of debate in Philosophy of Mind as to whether Mental States are identical with physical Brain States, or what sort of relation could be said to hold between the two.

However, it can be argued that Evolutionary Psychology is not committed to any particular answer to this question, being potentially compatible with Supervenience, Interactionism, Epiphenomenalism and both Token and Type physicalism, for example. Nevertheless, some people remain skeptical about any form of reduction from psychology to biology, and question its validity as an approach.

Why then, is the accusation of reductionism commonly used as a criticism of Evolutionary Psychology, and not say, as a criticism of Neuropsychopharmacology?: a discipline in which an implicit premise as regards psychology is that all states of mind, including both normal and drug-induced altered states, and diseases involving mental or cognitive dysfunction, have a neuro-chemical basis at the fundamental level (though there has been some criticism on this subject). The reason is that Evolutionary Psychology is a controversial field in itself, and to quote Richard Dawkins: "'reductionism', like sin, is one of those things only mentioned by people who are against it." The Blind Watchmaker, 1986 p.13. Here Dawkins makes a distinction between "direct" and "hierarchical" reductionism: organisms can be described in terms of DNA, DNA in terms of atoms, atoms in terms of sub-atomic particles etc; but knowledge of sub-atomic particles will not directly explain animal or human behavior, nevertheless, one can make adequate explanations and predictions at higher levels.

Issues in ethics

That human psychology may be determined by our biology, which is shaped by our evolutionary past, is an important idea for those involved in ethics. The implications are as broad and varied as the field of ethics itself however, but generally, it is thought that Evolutionary Psychology describes factors which limit our free will, in that it can be seen to imply that we behave in ways in which we are ‘naturally inclined’. Evolutionary Psychology is not in itself of course a theory of ethics, it merely states what is, not what ought to be, but this idea of ‘natural inclination’ is a recurring theme in ethics, arising not just out of Evolutionary Psychology, but almost all of the social sciences.

To quote J. Mizzoni from his article Ruse's Darwinian ethics and Moral Realism: “There are some moral philosophers (e.g., Thomas Nagel) who believe that evolutionary considerations are irrelevant to a full understanding of the foundations of ethics. Other moral philosophers (e.g., J.L. Mackie) tell quite a different story. They hold that the admission of the evolutionary origins of human beings compels us to concede that there are no foundations for ethics.” As we can see, the matter is subject to debate, some believing that evolutionary considerations are correct and necessary, others that they are incorrect and a form of the naturalistic fallacy, and others indeed that they are morally harmful whether correct or not. This idea of the supposed moral harm done by bringing together the social sciences and ethics is arguably where the greatest controversy lies.

See also: Ethics and evolutionary psychology

Empirical evidence

Some commentators, like philosopher David Buller, agree with the general argument that the human mind has evolved over time but disagree with the specific claims evolutionary psychologists make. Buller has argued, among other things, that the so-called Cinderella Effect, the argument that there are gender differences with respect to sexual jealousy, and the contention that the mind consists of thousands of modules, are unsupported by the available empirical evidence. [1] (But see Daly and Wilson's response to Buller)

An alternative to the "mental module" view of how human minds evolved is offered by cognitive psychologist Merlin Donald. He argues that over evolutionary time the mind has gained adaptive advantage from a general problem solver. Donald articulates this view in his book "A Mind So Rare: The Evolution of Human Consciousness" [2].

Another criticism regarding empirical evidence is a perceived lack of cross-cultural proofs. Many empirical studies come from a single culture. In these cases it is unknown if discoveries hold across all cultures.

Some references for rebuttals to criticisms of evolutionary psychology

• Alcock, John (2001). The Triumph of Sociobiology. Oxford: Oxford University Press.

• Barkow, Jerome (Ed.). (2006) Missing the Revolution: Darwinism for Social Scientists. Oxford: Oxford University Press.

• Clarke, Murray (2004). Reconstructing Reason and Representation. Cambridge: MIT Press.

• Pinker, S. (1997). How the Mind Works. New York: W.W. Norton & Co.

• Pinker, S. (2002). The Blank Slate: The Modern Denial of Human Nature. New York: Viking.

• Richards, Janet Radcliffe (2000). Human Nature After Darwin: A Philosophical Introduction. London: Routledge.

• Segerstrale, Ullica (2000). Defenders of the Truth: The Battle for Science in the Sociobiology Debate and Beyond. Oxford: Oxford University Press.

• Miller, Geoffrey (2000). The Mating Mind: How Sexual Choice Shaped the Evolution of Human Nature. New York: Random House Inc.

References

• Barkow, Jerome; Cosmides, Leda; Tooby, John (1992) The Adapted Mind: Evolutionary Psychology and The Generation of Culture ISBN 0-19-510107-3.

• Buss, David, ed. (2005) The Handbook of Evolutionary Psychology. ISBN 0-471-26403-2.

• Buss, D.M. (2004). Evolutionary Psychology: The New Science of the Mind. Boston: Pearson Education, Inc.

• Ghiselin, Michael T. (1973). Darwin and Evolutionary Psychology. Science 179: 964-968.

• Wright, Robert (1995). The Moral Animal: Why We Are the Way We Are: The New Science of Evolutionary Psychology. ISBN 0-679-76399-6.

• Hilary Rose, Steven P. R. Rose, Charles Jencks, Alas, Poor Darwin: Arguments Against Evolutionary Psychology, Harmony Books, 2000, ISBN 0609605135

• Sewell, Graham, Yabba-Dabba-Doo! Evolutionary Psychology and the Rise of Flintstone Psychological Thinking in Organization and Management Studies, Human Relations, Vol. 57, No. 8, 923-955 (2004)

Also see books listed at the Human Behavior and Evolution Society.

See also

• Behavioural genetics
• Dual inheritance theory
• Evolutionary developmental psychology
• Evolutionary educational psychology
• Evolutionary physiology
• Philosophy of psychology
• Human behavioral ecology
• Psychoanalytic Theory "A Fundamental Revision"
• List of evolutionary psychologists
• List of publications on evolution and human behavior
• Gene-centered view of evolution

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