stylistic:tone
Bone thickness

In 2004, Noel Boaz and Russel Ciochon suggested it was a result of a cultural practice, wherein H. erectus would fight each other with fists, stones, or clubs to settle disputes or battle for mates, since the skull is reinforced in key areas. The mandible is quite robust, capable of absorbing heavy blows (no "glass jaw"); the heavy brow ridge protects the eyes, and transitions into a bar covering the ears, connecting all the way in the back of the skull, meaning blows to any of these regions can be effectively dissipated across the skull; and the sagittal keel protects the top of the braincase. Many skullcaps bear usually debilitating fractures, such as the Peking Man skull X, yet they can show signs of surviving and healing. Anthropologist Peter Brown suggested a similar reason for the unusual thickening of the modern Australian Aboriginal skull, a result of a ritual popular in central and southeast Australian tribes where adversaries would wack each other with waddies (sticks) until knockout.