Paleopathological Evidence in Support of a Defensive Function for Homo erectus Skull Form

Franz Weidenreich was a trained medical doctor and had worked most of his career in medical institutions in Germany. It is likely that he had more than a passing familiarity with the effects of head trauma, although he did not publish on this subject early in his career. We believe that Weidenreich's identifications of healed depressed fractures on the skulls of Homo erectus should be taken much more seriously than they have been. Consequently, we undertook a systematic reexamination of Weidenreich's evidence for cranial bashing in Homo erectus using all the casts of the excavated remains from Longgushan.

In Weidenreich's final analysis, he attributed some ten depressions or defects in the skulls from Longgushan to hominid agency.14 He recanted on some earlier claims, ascribing this damage instead to carnivores. Other damage is clearly geological—crushing from the weight of overlying sediment and impressions in the bone from rocks pushed into the fossilizing bone by the enclosing sediment. But a number of the remaining depressions in the Homo erectus skulls from Longgushan match closely the size, form, and even location of healed depressed fractures seen in modern human skulls.

The face and lower jaw frequently bear the brunt of frontal assaults. Are there any anatomical indications that Homo erectus evolved to taking it on the chin, as would be expected if our argument is correct? Broken jaws in modern barroom brawls frequently occur just behind the chin region.15 In Homo erectus this area of the mandible on both sides of the

Healed depressed fractures are depressions in the skull resulting from a blow heavy enough to break the outer table of bone but not to cave in and displace a fragment of bone. The top view is a contemporary Homo sapiens (United States) showing a healed depressed fracture near the crown of the head along the sagittal suture. Middle and bottom views show the depressed fracture in Homo erectus Skull X from Longgushan in a similar location.

jaw is strengthened to form a thickened mass of bone termed by Weidenreich the torus mandibularis. Like the various cranial tori there has never been an adequate functional anatomical explanation for the torus mandibularis. It does not serve for the attachment of any muscle and its thickness is not in the area of support for chewing strength. We believe that the torus mandibularis is also an adaptation to withstand trauma to the jaw and lower face.

Broadly speaking, cranial pachyostosis in Homo erectus evolved as a result of sexual selection, a subset of principles of Darwinian natural selection that comes into play in social species, the sexes of which compete for mates. Homo erectus uniqueness in skull form then represents a detour in the broad march of human evolution along the course of an enlarging brain and a decreasing emphasis on large teeth.

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