By the final third of the twentieth century, evolutionary concepts were increasingly penetrating psychological theories. For example, both attachment theory and Jungian psychology borrow from evolutionary biology. The field of sociobiology explicitly applies the principles of evolutionary theory to the understanding of social behavior. This approach assumes that at least some part of social behavior is genetically based and therefore has been acted upon by evolution. In other words, when a behavior has survived across thousands of generations, it most likely serves an evolutionary purpose. This approach was first applied to the study of non-human animals; it wasn’t until the 1970s that evolutionary theory was rigorously applied to the study of human social behavior.

Evolutionary psychology is an outgrowth of sociobiology that focuses specifically on the evolutionary roots of human behavior.