It is crucial to understand that kinship relationships are quite distinct from biological relationships. Kinship systems vary greatly, but as physiological processes are the same everywhere, these variations are clearly social rather than biological. There is more to it than this however. It had long been conventional to distinguish social parents (†pater and †mater) from physiological ones (†genitor and †genetrix), but John Barnes (1961) introduced a further distinction between genitor and genetrix, the supposed biological parents of the child, and the genetic father and mother from whose sperm and ovum the child was actually produced. Like mater and pater, genetrix and genitor are sociallyascribed roles, assigned according to prevailing ideas about the biology of *conception, combined with assumptions about the sexual activities of possible parents. Of these three levels-social kinship, *emic views about physical kinship, and genetic relationship - social anthropology is concerned only with the first two. It deals not with biology itself, but with biological kinship as culturally defined by the society concerned.