Peter Brown, a paleoanthropologist at the University of New England in Armidale, Australia, has investigated skull thickness in modern and historical Australian Aboriginal populations, whose cranial bones are the thickest of any living H. sapiens. In a sample of 430 Aboriginal crania, Brown found evidence of healed depressed fractures on the frontal or parietal bones in 59 percent of the female crania and in 37 percent of male crania. Depressed fractures occurred in these people and they survived; undoubtedly, many others did not. His findings led Brown to hypothesize that the thick skull vaults of the Aboriginals may have evolved as a consequence of the traditional method for settling conflicts.
A similar explanation may account for the evolution of pachyostosis and other unique features that strengthened the H. erectus skull. We are reasonably confident that the distinct anatomical features, as well as the healed fractures that have been preserved in the fossil record, are primarily a response to violence within the species. We can only speculate about whether the violence involved ritualized fights with clubs or rocks among hot-headed young males competing over females, or instead revolved around other kinds of conflict. But we would lay bets that, as in many other species, we are detecting the results of sexual selection.
If H. sapiens evolved from H. erectus, why dont we, too, have thickened cranial bones? If modern children had thicker skulls, for instance, significantly smaller numbers of them would suffer serious head injuries when they crash on bicycles, skateboards, and snowboards. Theoretically, a species could have both a commodious skull to house an enlarged brain and a thick, heavily armored skull for protection. But reality steps in when the weight of such a structure has to be supported and balanced atop the spine. Cranial bone may have become thinner in modern humans simply to reduce skull weight.
, your browridge is wimpy.
