Human societies share a large number of complex social traits relating to kinship, which together constitute what is called here the human kinship configuration. I use a comparative phylogenetic approach to show that each of the traits making up that configuration has an evolutionary history and hence a biological foundation. The origin of many complex traits may be explained in terms of emergent products of the combination of more elementary features present in other primate species, whereas other traits appear to emerge from the combination of primate features with uniquely human cognitive abilities. The resulting composite traits thus have a compounded biological foundation, but at the same time they are always manifest under specific cultural—formal and semantic—expressions in any society. The traits may thus be seen as open-ended, culturally polymorphic and polysemous categories, or sociocultural categories, with the categories themselves having a biological foundation while their contents are culturally defined. Importantly, those categories need not be cross-culturally universal even though they are natural; their presence or absence in a given society is culturally modulated. I argue that a large number of such categories operate as an interface that helps bridge the gap between human biology and the sociocultural realm and that information on that interface is required for understanding how human nature structures cultural diversity.