@inbook{DurrantEllis2003,
author = {Durrant, Russil and Ellis, Bruce J.},
title = {Evolutionary psychology},
editor = {Gallagher, M. and Nelson, R. J. and Weiner, I. B.},
journal = {Handbook of psychology: Biological psychology},
year = {2003},
volume = {3},
pages = {1-33}
}
Central assumption of evolutionary psychology: "the human brain is comprised of a large number of specialized mechanisms that were shaped by natural selection over vast periods of time to solve the recurrent information-processing problems faced by our ancestors." [p1]
Evolutionary psychology seeks to identify these information-processing problems, develop models that attempt to explain how the human brain evolved to solve them, and test the models (Buss, 1995; Tooby & Cosmides, 1992).
Evolutionary psychology is a burgeoning field. [p1]
Evolutionary psychologists employ four levels of explanation, which are ordered in a hierarchy. In order from top to bottom, they are: metatheoretical assumptions of modern evolutionary theory, middle-level evolutionary theories, hypotheses, and predictions. [p2-3]
Metatheory Level of Analysis:
Metatheoretical assumptions are a guiding light for evolutionary psychologists, demarcating what lines of research should and should not be pursued. Furthermore, they tie together a wide variety of middle-level theories.[p3]
Four metatheoretical assumptions are held by all evolutionary scientists: natural selection, adaptation, sexual selection, and inclusive fitness theory.[p3]
Natural Selection:
Certain phenotypic characteristics of an organism (both physical and psychological) confer a survival and reproductive advantage. Provided these characteristics are heritable, over time they will become more prevalent in a population of organisms.[p4]
Adaptation:
These phenotypic characteristics referred to above are called adaptations. They have biological functions (e.g. the immune system protects an organism from disease).[p5]
Not all changes in the characteristics in a population are adaptations: By-products (traits that developed concomitantly with an adaptation), and noise (traits that develop randomly) are selectively neutral or even deleterious traits, and are therefore considered nonadaptations.[p5]
An important task of the evolutionary psychologist is to tease apart adaptations from nonadaptations. One such method for doing so is to see whether or not a trait demonstrates adaptive complexity (many parts or systems working together to grant the organism a selective advantage); such a complex system is unlikely to have evolved due to chance or as a byproduct of another trait.[p5-6]
As in other scientific domains, in situations where it is not clear whether a trait is an adaptation the preferred hypothesis is one that both explains what is currently known (Haig & Durrant, 2000; Holcomb, 1998) and leads to new knowledge (Ketelaar & Ellis, 2000).
Sexual Selection:
Some traits serve only to enhance an organism's ability to reproduce, sometimes even placing it at a survival disadvantage (e.g. extravagant feathers in some species of birds may impede their movement, making them easier to be captured by prey, but also allow them to attract more mates). [p6-7]
Inclusive Fitness Theory:
The "core idea of inclusive fitness theory is that evolution works by increasing copies of genes, not copies of the individuals carrying the genes". So, somewhat counterintuitively, altruism (self-sacrifice) can be selected because, while it provides a survival disadvantage for the single organism, it provides a survival advantage for its genetic code. [p7]
There are several special metatheoretical assumptions that evolutionary psychologists endorse: that psychological mechanisms are the main unit of analysis, that there are many such mechanisms, and that they are adapted to a specific environment[p7].
Psychological Mechanisms as the Main Unit of Analysis:
In the terminology of evolutionary psychologists, psychological adaptations are called psychological mechanisms.[p8]
Since the study of the evolution of behaviour and cognition is the goal of evolutionary psychology, psychological mechanisms, not genes, should be the main unit of analysis. This is because genes act only indirectly on behaviour and cognition.[p8]
One criteria for identifying psychological mechanisms: they solved survival and reproductive problems faced by our ancestors; they take in selective information from the world as input; use rules and procedures to process this information; generate output that solves adaptive problems (Buss, 1999).
Domain Specificity of Psychological Mechanisms:
Evolutionary psychologists posit that there are a multitude of psychological mechanisms that are specially designed for specific adaptive problems (domain-specific), as well as all-purpose mechanisms for solving more general problems and integrating information from across the disparate mechanisms of the mind (domain-general). [p9]
Evidence for domain-specific mechanisms: organisms face a wide variety of adaptive problems that require a wide variety of problem-solving strategies (e.g. mate and food selection) that domain-general mechanisms are insufficient in handling. [p9]
Even domain-general mechanisms seem to be at least partially informed by domain-specific mechanisms (e.g. Garcia & Koelling, 1966).
Studying domain-specific mechanisms offers a "theoretically guided taxonomy of mental processes".[p10]
The Environment of Evolutionary Adaptedness:
Adaptations arise as a solution to problems faced in specific environments.
The environment in which an adaptation arose is called its environment of evolutionary adaptedness (EEA). Although the problems presented to humans by modern environments are in many ways quite similar to those in the EEA for our psychological mechanisms, they differ in others, which can result in dysfunctional behaviour (e.g. the maladaptive drug cocaine acts on the adaptive dopamine reward system).[p10]
The Middle-Level Theory Level of Analysis
Middle level theories provide an empirical link between metatheoretical assumptions and the real world, indirectly providing evidence for the metatheory. Moreover, they employ the basic logic provided by metatheoretical assumptions to expand knowledge. [p11]
Two examples of middle-level theories are Parental Investment Theory and Good Genes Selection Theory.
Parental Investment Theory:
The theory that "the sex that invests more in offspring should be more careful and discriminating in mate selection, should be less willing to engage in opportune mating, and should be less inclined to seek multiple sexual partners", with the opposite holding true for the sex that invests less in offspring. In the case of humans, due to the reproductive burdens placed on females in the form of the resource-intensive process of egg production, a long gestation period, a potentially harmful childbirth, and the years of care needed to raise a child, they have much more parental investment than males--a trend that is nearly universal across species. [p12]
Parental investment theory predicts that parental investment in males should only evolve when there is a great degree of certainty that the offspring to which he is devoting resources is his own. And whenever it does evolve, behaviour that increases this certainty should also be selected ('mate retention strategies'). Consistent with parental investment theory, these behaviours are observed across a wide variety of species (e.g. sexual jealousy, possessiveness, and threats of violence are mate retention strategies for human males; a barbed penis that removes any sperm from prior matings is a mate retention strategy for male damselflies). [p13]
Good Genes Sexual Selection Theory:
The theory that "the outcome of mate choice and intrasexual competition will be determined by traits that indicate high genetic viability" (Andersson, 1994; Williams, 1966). Although these traits are sometimes seemingly superficial (e.g. the extravagant plumage of some birds), they are usually costly to produce, and therefore only the organisms with the best genes will possess them. [p14-15]
Direct phenotypic benefits are the more immediate benefits that one mate can provide another (e.g. resource-accruing potential). These benefits are not always mutually exclusive from good genes selection (e.g. extravagant plumage in birds indicates both good genes and a lack of parasites). [p15]
The Hypothesis Level of Analysis
"[A] hypothesis is a general statement about the state of the world that one would expect to observe if the theory from which it was generated were in fact true". Hypotheses vary in terms of their adherence to middle-level theory from firm hypotheses, to expectations, to hunches. [p17]
An example of a firm hypothesis derived from the good genes sexual selection theory: because good genes indicators require a strong metabolism to develop, individuals who possess them should be healthier than those who do not. [p18]
The Prediction Level of Analysis
Predictions are "specific statements about the state of the world that one would expect to observe if the hypothesis were in fact true". They are "explicit, testable" forms of hypotheses. Because of this concrete nature of predictions, they play a critical role in determining whether or not a middle-level theory is correct. [p19-20]
An example of a hypothesis generated by good genes sexual selection theory: "More symmetrical individuals should have better mental and physical health, better immune system function, and lower parasite loads than should less symmetrical individuals". [p20]
The Future of Evolutionary Psychology
Evolutionary psychology seeks ultimate explanations (i.e. why do organisms have a given trait), which are complementary with the proximate explanations (i.e. how traits work) offered by psychology proper; each informs the other. As evolutionary psychology continues to mature, its unique perspective will continue to have substantial effects on psychology as a whole.