If we don't get our act together in time and we push this planet past its limits, to the point where things get disaster-movie bad, at the very least we can take solace in the fact that we've been there once before. According to new research out of Stanford University, the human species was on the brink of extinction 70,000 years ago due to an extended drought. It shrunk the human population to a number perhaps as low as 2,000.