Those Pesky Humans
They just keep reproducing, though far more slowly than anticipated by doomsayer Paul Ehrlich in his famous Population Bomb. Ehrlich is hardly contrite, telling the New York Times that the earth's optimal population is two billion. "I have severe doubts that we can support even two billion if they all live like citizens of the U.S.," he said. "The world can support a lot more vegetarian saints than Hummer-driving idiots."