Evolutionary theory came of age with the publication of Charles Darwin's Origin of Species (1859), in which he argued that all organisms, living and dead, including humans, are the end result of a long, slow, natural process of development from one or a few simple life forms. Believing this new world history to be the death knell of traditional ways of thinking, many were inspired to find evolutionary parallels in other fields, including ethics—in both evolution of appropriate guides for proper human conduct (substantive ethics) as well as the justificatory foundations for all such social behavior (metaethics).

At the substantive level the evolutionary ethicist's usual point of departure was Darwin's own suggested mechanism of change—the "natural selection" of the "fittest" organisms in the struggle for existence—seeking to find an analogue in human conduct. Although this philosophy became known as Social Darwinism, its widespread popularity...