Somewhere between 300,000 and 250,000 years ago, humans popped up. Until about 25,000 years ago, humans existed is small family groups, and were hunter /gatherers. Then all over the globe, towns and cities emerged, along with farming, kicking off empires and civilizations. Why? Why didn't some guy, 200,000 years ago, figure out farming? What took so long? And what happened 25,000 years ago, when cavemen, all over the world, decided to give up hunter/gathering, move to a city and become vacuum cleaner salesmen?