The human, chin revisited: what is it and who has it?

Although the presence of a "chin" has long been recognized as unique to Hom o sapiens among mammals, both the ontogeny and the morphological derails of this structure have been largely overlooked. Here we point out the essenti al features of symphyseal morphology in H, sapiens, which are present and w ell-defined in the fetus at least as early as the fifth gestational month. Differences among adults in expression of these structures, particularly in the prominence of the mental tuberosity, are developmental epiphenomena an d serve to emphasize the importance of studying this region in juveniles wh enever possible. A survey of various middle to late Pleistocene fossil homi nids for which juveniles are known reveals that these features are present in some late Pleistocene specimens assigned to H. sapiens, but not in all o f the presumed anatomically modem H. sapiens (i.e., Qafzeh 8, 9, and 11). T he adult specimens from Skhul, as well as the adult Qafzeh 7 specimen, are similarly distinctive in symphyseal morphology. Neanderthals are quite vari able in their own right, and they as well as other middle to late Pleistoce ne fossils lack the symphyseal features of H. sapiens. Some of the latter a re, however, seen in the Tighenif (Ternifine) mandibles. (C) 2000 Academic Press.