Besides what others pointed out, there's evidence that the proto-humans of 500 thousand years ago hadn't developed spoken language yet [1]. So it was hard to te

Besides what others pointed out, there's evidence that the proto-humans of 500 thousand years ago hadn't developed spoken language yet [1]. So it was hard to teach what you knew to people living next to you, let alone pass on knowledge to other generations. [1] http://en.wikipedia.org/wiki/Origin_of_speech#When_did_speech_evolve.3F http://en.wikipedia.org/wiki/Origin_of_speech#When_did_speec...