Evolutionary psychology is an approach to psychology that attempts to explain psychological traits using the Theory of Evolution, by considering them as adaptations to their environment, 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 heart or the immune system, into the field of psychology, and to approach psychological mechanisms.
Evolutionary psychology is not an area of study, such as memory or attention but instead is a way of viewing psychology and framing research. Research has focused on a diverse range of topics from facial recognition to mate to choice to altruism. It is one of the youngest paradigms in psychology formalizing in the 1980s. Only within the last ten years have universities created specific departments for evolutionary psychology and conferred specific degrees in the field.
Evolutionary psychology obviously has deep roots with Charles Darwin and his theory of evolution. But the connection is deeper than that. Darwin is sometimes described as the first evolutionary psychologist. In the closing pages of his work The Origin of Species he states:
"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." 
However, most of psychology took a very different path for the next 60 years focusing on behavioral psychology, while evolutionary biology focused mainly on mechanisms of evolution and united genetics and evolution. Several important individuals in psychology and biology however tried to accomplish what Darwin had pointed to.
William James in his book Principles of Psychology focused a great deal on instincts and advocated a functionalist approach to psychology. RA Fisher the famous statistician and evolutionary biologist, as well as J. B. S. Haldane, helped define a mathematical base for many of the ideas that would later come to dominate evolutionary psychology.
During the peak of the cognitive revolution in psychology two very important works were published. The first was George C. Williams' Adaptation and Natural Selection in 1964. This was an extremely important book in evolutionary biology; it advocated a gene-centric view of evolution and used mathematical models to demonstrate that currently vogue theories of group selection were impossible. Two years later in 1966 W.D. Hamilton would use the concepts of gene-centric evolution to argue that evolution could support development of traits that did not directly favor the individual. This would become known as inclusive fitness and Hamilton's rule would later serve as bedrock for future work in evolutionary psychology.
The 1970s brought about the first recognizably modern research in evolutionary psychology. One significant development was the publication by evolutionary biologist Robert Trivers on his theories of reciprocal altruism, parental investment theory, and parent-offspring conflict. All of these ideas made use of Williams' and Hamilton's work. Another important event was E.O. Wilson's publication of Sociobiology. Wilson's work attempted to explain such mysterious of evolution as the peacock's tail and the social structure of ants. He also advocated the explanations he found be applied to human behavior. His ideas were highly controversial and received a lot of political backlash, though the scientific community was mostly positive.
In many ways sociobiology is very similar to evolutionary psychology, but with the size of the political pressure and negative press surrounding sociobiology the term fell out of favor in the early 80s. Focus shifted from studying the evolutionary adaptiveness of specific behaviors, to studying the adaptiveness of the mechanisms which produce those behaviors. Many students and proponents started using the term evolutionary psychology. This would become the more accepted phrase.
Most of the early work focused on demonstrating that the core belief in a universal human nature that could be elucidated from an evolutionary perspective was a viable idea. David Buss did a cross cultural study that examined 32 groups all over the world to show that there was a gender difference in preferences for short-term mates, but remarkable similarity for long-term mates. This prediction actually stemmed from evolutionary ideas of Trivers and concepts such as Bateman's principle. This dataset was also important because it showed that even a diverse range of cultures shared a common psychology.
By the 1990s the field had expanded considerably and gained a lot of recognition. Several Journals dedicated to evolutionary psychological research were started, including Evolution and Human Behavior which is run by the Human Behavior and Evolution Society.
Basics of the field
There are several major principles usually formulated by proponents:
- The brain as a physical system - this is usually analogous to a computer, it is thought by proponents that the brain is responsible for taking in information from the environments, computing a solution for optimal behavior and then directing that behavior.
- Selection shaped the neural circuits in the Environment of evolutionary adaptedness - Proponents of the theory believe that selection shaped the psychological responses of the organism, but that this selection is rooted in the evolutionary past. One common example of this is the preference for fat in food. In the EEA it would have been a great benefit but in the modern age it causes health concerns, but because behavior was selected for in the EEA and there hasn't been enough time people still eat fatty foods in abundance.
- The conscious mind is only a small part of psychology - Most of psychology now recognizes that there is an extensive unconscious mind that can control behavior and motivation. One does not have to know why he is doing something in order to do it, or even really ware of what he is doing. Proponents of evolutionary psychology believe that much of the "why" is hidden from conscious thought.
- The mind is domain-specific not domain-general - Evolutionary psychologist believe that the mind is made up of modular elements that evolved separately to address separate problems. This is opposed to thinking of the mind as a general problem solving system with out specific domains of processing.
Adaptationist perspective and functional design
Evolutionary psychology takes an adaptationist perspective to psychology. In evolutionary biology hypothesis about historical reasons for a particular trait can range from drift, to phylogenetic constraint. Adaptationist are primarily interested in those traits shaped directly by selection. In order to argue that a given trait is an adaptation evolutionary biologist and psychologist usually turn to ideas of functional design.
If a particular trait appears to be designed to solve a particular problem evolutionary proponents theorize that selection shaped it for that function. The only mechanism that proponents of evolution postulate that can create functional design is selection. Drift, constraint, neutral selection and byproducts do not create functional design.
Tinbergen's four questions
Evolutionary psychologist rarely claim that their ideas are in direct competition with other hypothesis in cognitive or behavioral or developmental psychology. Instead they say that multiple causes are different levels of explanations.
This idea comes from Tinbergen's four questions. The evolutionary psychologist addresses casual relationships in deep time and focuses on ultimate causation. Developmental psychologist, cognitive psychologist or even neurologist focus on proximate or ontogenetic causes.