National Geographic: After nearly going extinct 150,000 years ago, humankind split into small groups–living in isolation for nearly a hundred thousand years before "reuniting" and migrating out of Africa, a new gene study says. At one point our species may have been down to as few as 2,000 individuals, probably due to climate change–a longstanding theory bolstered by the new findings. The research fills a gap in our understanding of what was happening in Africa before humans first left …