[patrickp]

In addition, we can survive and grow quite happily on a vegetable-only diet, whereas we cannot survive on a meat-only diet, as proper predators do!

Interestingly, the physiology that most closely matches ours is not any of the apes, but pigs. It's thought that this is because our natural diet is very similar to that of omnivorous pigs. That's why pigs are so often used for trials of drugs etc to be used for humans, and why pigs are mooted as potentially the best non-human bet for sourcing transplant material - size also has to do with this, of course.

My personal opinion is that, along with the benefits accruing from socialisation, tool use was what drove the evolution of our brains and nervous systems. Both language use and dexterity would be advantageous in developing these skills, so the development of the nervous system, plus that of the organs of manipulation and communication (mostly hands, voices and faces) would tend to produce the most successful individuals.

In fact, a chimpanzee, for instance, doesn't really posses comparatively more musculature than a human, but is considerably stronger. The reason for this is that a chimp's muscles are connected to its skeleton in ways that produce much greater leverage; at the same time, this means that a chimp has nowhere near the dexterity that a human has.

The fact is that humans, individually, make appallingly poor predators. What gives them their edge is social cooperation and the development of tools such as weapons. In other words, humans could not become successful predators until the development of communication and toolmaking skills enabled this. But then, while it was humans' evolutionary prowess that enabled them to be able to become successful predators, at the same time this evolutionary prowess laid the grounds for humans to become agricultural creatures, a way of life offering far greater opportunity to develop those skills of toolmaking and socialisation further, and offering much greater security for the future.

Specialising in predation has always been, essentially, a sideline for humans. While primitive societies may have had (and some still do today) individuals who have specialised in hunting, it's always been the skills of communication, toolmaking and farming that have taken these societies forward, and, probably, overspecialising in hunting that has held them back.