One of the major conflicts in the social sciences since the Second World War has concerned whether, and to what extent, human beings have a nature. One view, traditionally associated with the political left, has rejected the notion that we have a contentful nature, and hoped thereby to underwrite the possibility that we can shape social institutions by references only to norms of justice, rather than our innate dispositions. This view has been in rapid retreat over the past three decades, in the face of an onslaught from several different strands of psychology purporting to show that human nature has a content. In this paper, I argue for a third view: that human beings have a contentful nature, but that nature is uniquely flexible and therefore places relatively few constraints on the shape of our social institutions. Human beings are shaped, by nature, to be cultural animals. We are innately disposed to imitate the behavior of those around us, to a far greater degree than other animals: this disposition toward overimitation allows us to construct local traditions of behavior and thereby to adapt to an enormous variety of environments. These facts, in turn, ensure that human populations live embedded in local forms of life; thus our nature entails that we are deeply cultural animals.