"Anthropologists believe early humans evolved in Africa and then moved out from there in successive waves. However, what drove their migrations has been a matter of conjecture. One new explanation is climate change."
"Anthropologist Anders Erikkson of Cambridge University in England says the first few hardy humans who left Africa might've gone earlier but couldn't. Northeastern Africa — the only route to Asia and beyond — was literally a no man's land.
'The people couldn't really couldn't leave,' he says. 'The climate was too arid and too hot, so humans were bottled up.'
Eventually they got out of the bottle — we know that from the trail of fossil bones and stone tools they left behind. And recently, scientists have learned to read genetic mutations in current populations to track where our ancestors went for the past 70,000 years or so."