Evolutionary psychology (Barkow, Cosmides, & Tooby, 1992; Buss, 1995) is an approach to understanding the mind that draws on two profoundly important theories. The first is Darwin's theory of evolution by natural selection, which underpins the idea that psychological mechanisms are adaptations (cf. Darwin, 1859, 1871). Darwin's theory explains how complex biological organisms can be constructed by natural selection operating on heritable differences between individuals that affect reproductive fitness. The second theory on which evolutionary psychology draws is the theory of computation, which underpins the treatment of psychological mechanisms as information processors and minds as computers. The originator of the modern theory of computation was the mathematician Alan Turing (cf. Turing, 1936-1937). Turing developed the abstract definition of a universal computer on which contemporary computer science is founded, and was able to prove some fundamental theorems about the capacities and limitations of symbolic information-processing systems. The universal machine concept is as important for our thinking about the nature of machines as natural selection is for thinking about the origins of complex biological systems.