A brief comment on the tooth form and diet issue. This is really a very
old chestnut indeed. While it is perfectly possible to attribute subtle
changes in dentition to changes in diet in most species, the fact that
Homo has been processing its food for at least 2.5 million years means
that the pattern of adaptation has become somewhat uncoupled. Broadly
early hominids have broader and flatter molars than their primate
ancestors suggesting a somewhat tougher diet, perhaps more dry and
fibrous plant material as opposed to the fruit and soft leaf diet of
chimps. However given that chimps and baboon eat significant quantities
of meat and yet have relatively high-crowned teeth this all starts to look
a little wobbly. Orang-utans have superficially more human looking teeth
but little is known of their evolutionary ecology. From the early hominid
pattern we see the megadonty of the robust 'australopithecines' with
their large mill-stone like molars popularly but not exclusively attributed to
a diet of tough vegetable matter. The progressive reduction of the human
dentition in the Homo lineage is generally held to represent a shift to
food processing before it was put in the mouth rather than a change in
diet per se. Thus the flat molars of humans are probably explained by a
shift to tougher/gritier food than the other great apes around 5 million
years ago, the side to side motion facilitated by the reduction in the
size of the canine and the loss of the canine/premolar complex. But by 2
million years ago Homo was a committed meat eater; that this is not
reflected in the teeth merely emphasizes the role of stone tools.

Mark Leney
Institute of Biological Anthropology
Oxford