Charles Darwin observed that closely related organisms typically varied across geographic locations separated by physical barriers and across geological periods separated by long time intervals. Darwin reasoned that a process of Natural Selection, analogous to the selective breeding of domestic animals, created differential survival and reproduction of certain individuals within a population. Eventually, over many generations, populations were transformed by natural selection into new species. A second Englishman, Alfred Russel Wallace, independently developed the concept of Natural Selection and the general theory was presented to the Scientific community with excepts from both Darwin and Wallace in 1858.
An unshakable foundation for Darwinian evolution theory was provided by the development of modern genetics. Understanding that traits were transmitted as discrete, non-blending units (genes) led to an understanding of evolution as a sustained, directional shift in population gone frequencies. Spontaneous changes in genes (mutations) provide new raw material for evolutionary change. Delineating the chemical structure of DNA, the molecule of heredity has made it possible to study evolution at the molecular level.
From the inception of evolutionary theory, it was understood that behavioral traits were shaped by Natural Selection just like morphological and physiological traits. Charles Darwin understood this, as did the American philosopher and psychologist William James. William James founded the Functionalist approach in psychology, which is based on the idea that complex mental functions are evolved traits.
This adaptationist approach to human psychology fell out of favor for nearly a century as a consequence of a number of tragic historical events. Darwinian theory was used as a prop to support a number of versions of the Naturalistic fallacy. Social Darwinists argued that the exploitation of the poor by the rich was just the natural order of things and Nazi death camps were created to eliminate “inferior” races. Partially as a result of these abominations, behavioral theories based on environmental determinism were embraced by psychologists (behaviorists) and anthropologists (cultural relativists).
Discoveries in the science of ethology (animal behavior) and sociobiology, such as the concept of inclusive fitness provided the basis for the modern reemergence of an adaptationist approach to human psychology, evolutionary psychology. Evolutionary psychology focuses on the evolved psychological mechanisms that comprise the mind as the central locus of behavioral adaptation. Evolutionary psychologists use information from a variety of sources to identify which aspects of human behavior represent evolved psychological mechanisms. The validity of the hypothesized adaptations is tested by generating and verifying specific predictions that are implied by evolved functionality as well as testing predictions that follow from alternative hypotheses. The interdisciplinary nature of evolutionary psychology gives it an inherently sound scientific basis.