In this paper I argue that the “dynamic functionalism” of Dewey’s evolutionary approach to ethics – moral norms emerge to address specific problems but must be constantly readjusted to changing contexts – had its roots in the comparative jurisprudence of Sir Henry Sumner Maine and Oliver Wendell Holmes Jr. First, I will discuss the rise of the comparative sciences in the nineteenth century, part of the backdrop for the work of Maine and various evolutionary anthropologists. Next, I will examine Maine’s Ancient Law (1861), Edward Burnett Tylor’s Primitive Culture (1871), and Holmes’s The Common Law (1881), three related books that set up a dichotomy between existing custom and historical progress. Finally, I will show how this dichotomy was reflected in Dewey’s writing and teaching at the University of Michigan in the early 1890s, including “Anthropology and Law” (1893) and several courses in political philosophy.