The United Nations says that the world's population will reach 7 billion people this month. The approach of that milestone has produced a wave of articles and opinion pieces blaming the world's environmental crises on overpopulation. In New York's Times Square, a huge and expensive video declares that "human overpopulation is driving species extinct." In London's busiest Underground stations, electronic poster boards warn that 7 billion is ecologically unsustainable. In 1968, Paul Ehrlich's bestseller The Population Bomb declared that as a result of overpopulation, "the battle to feed humanity is over," and the 1970s would be a time of global …