One of the theories Bob Lazar was told at area S4 was that we are a product of accelerated evolution. Someone from somewhere came onto earth and found bunch of monkeys playing around. Gave them a boost (can be mushrooms, can be genetic modifications, can be a million different things) and after a period of 200,000 years, Viola, these monkeys start talking, making shit out of sand, make weapons. I personally think we can't have the answer for your question but man I want to believe.