Lewis Henry Morgan of Rochester, New York, lawyer and pioneer anthropologist, was the leading American contributor of his generation to the social sciences. Among the classic works whose conjunction in the 1860s gave modern anthropology its shape, Morgan's massive and technical Systems of Consanguinity and Affinity of the Human Family was decisive. Thomas Trautmann offers a new interpretation of the genesis of "kinship," and of the role it played in late nineteenth-century intellectual history.