Broadly speaking, ‘functionalism’ refers to a range of theories in the human sciences, all of which provide explanations of phenomena in terms of the function, or purpose, they purportedly serve. In the period spanning the last decades of the nineteenth century and the first half of the twentieth, virtually every human science generated a school that identified itself as functionalist, and in nearly every instance that school dominated its discipline for a time. Darwinian evolutionary theory provided the initial impetus to functionalist reasoning. But †Darwin’s multifarious argument admits of variable interpretation, so different constructions of his model yielded varieties of functionalism. The earliest schemes, those of psychology and economics, were promulgated at the turn of the century. These were not equally important, however; functionalist psychology was extremely influential, while functionalist economics was nearly inconsequential. But in both, the *individual was the basic unit of analysis, and individual action was conceptualized in terms of recursive processes of evolutionary adaptation. That is, both functionalist psychology and economics relied on an interpretation of the inherent nature of the human organism, and constituted fundamentally historical approaches to explanation.