Facing a violent past: Evolution of human ancestors' faces a result of need to weather punches during arguments, study suggests -- ScienceDaily
The reference above offers a hypothesis to explain why Australopithecus and other prehuman ancestors had such robust faces, with heavy bone structure. The suggestion is that the males fought a lot, including hitting each other in the face. Evolution then equips the prehumans with strong bones to resist damage.
We do know that more 'primitive' human societies are more violent than modern humans, so this kinda makes a kinda sense. However, I suspect that punching would not have been the main form of attack. After all, we know that, with the more fragile bones of modern human faces, hitting someone in the head is still likely to break wrist bones. It must have been more the case in earlier times. So, did they hit each other in the head with weapons? Or is this hypothesis so much bulldust?
PS. Something I just happen to know (weird for a person who hates boxing) is a tidbit about boxing history. Early boxing was bare knuckle, and mainly involved blows to the body, since hitting someone bare knuckle on the face or head hurt the puncher's fist like crazy, and sometimes broke bones. Since boxing gloves became adopted, hitting the face or head increased dramatically, with that becoming the primary target. The death rate during boxing bouts also increased substantially. Bare knuckle boxing very rarely resulted in death. Boxing with gloves kills frequently enough to add up to many boxing deaths each year. That is simply because gloved boxers hit their opponent in the head, where bare knuckle boxers do not. Not if they want to keep intact hand bones, that is.