"Certainly the first true humans were unique by virtue of their large brains. It was because the human brain is so large when compared with that of a chimpanzee that paleontologists for years hunted for a half-ape, half-human skeleton that would provide a fossil link between the human and the ape."

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It has actually been suggested that warfare may have been the principle evolutionary pressure that created the huge gap between the human brain and that of our closest living relatives, the anthropoid apes. Whole groups of hominids with inferior brains could not win wars and were therefore exterminated.

— Jane Goodall