Gracilization: evidence of humans domesticating themselves

"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.