After watching the Discovery Channel’s special on Ardipithecus Ramidus tonight, I was reading some reviews of recent evolution-themed books. One of the reviews had this paragraph referencing Nicholas Wade’s excellent Before the Dawn: Recovering the Lost History of our Ancestors :
In the lost history whose DNA-aided recovery Wade chronicles, one of the most interesting chapters covers “gracilization” — that is, “a worldwide thinning of the human skull” starting around 40,000 years ago. Why was it that, millenniums before the agricultural revolution, our ancestors became progressively lighter-boned and smaller? A crucial clue: The fossil record and contemporary breeding experiments alike confirm that domestication, whether accidental — as in the evolution of the dog from the wolf — or deliberate, induces pedomorphism, or the retention of juvenile features into adulthood. “Gracilization . . . occurred because early modern humans were becoming tamer,” Wade writes. “And who, exactly, was domesticating them? The answer is obvious: people were domesticating themselves. In each society the violent and aggressive males somehow ended up with a lesser chance of breeding. This process started some 50,000 years ago, and, in [primatologist Richard] Wrangham’s view, it is still in full spate.”
Based on the reconstruction of Ardi, it appears that we have been domesticating ourselves for a lot longer. One of the questions raised by Ardi was – what advantage did bipedal locomotion confer, why did it evolve so early in hominids? And a secondary question was, why did the Ardipithecus males have such small, non-combat worthy, canine teeth? The explanation offered during the special was: free hands allowed for more food gathering and transport back to the family or group. Males would no longer need to fight for access to females (as is the case in chimps and other great apes) if the females chose to mate with the males who were capable of bringing in more food. If the females did not have visible, easily detectable estrus, and exchanged frequent sex for food, then fully bipedal motion would be advantageous as compared to chimp-like knuckle walking.
For an alternative take on this (and just a very good summary of the Ardipithecus Ramadi papers in general) go here.