In a distinctly un-Malthusian fashion, population then took off. It hit two billion in the nineteen-twenties, and was three billion by 1960. In 1968, when Paul Ehrlich published “The Population Bomb,” predicting the imminent deaths of hundreds of millions of people from starvation, it stood at around three and a half billion; since then, it has been growing at the rate of a billion people every twelve or thirteen years. According to the United Nations, it reached six billion on October 12, 1999. (A baby boy born in Sarajevo, Adnan Mević, was, for symbolic purposes, designated the world’s six-billionth person and greeted at the hospital by U.N. Secretary General Kofi Annan.) For large and slow-to-reproduce mammals like humans, such a growth curve is, to put it mildly, unusual. Edward O. Wilson has called “the pattern of human population growth” in the twentieth century “more bacterial than primate.” Predicting where the numbers will go from here is, at least in the short term, pretty straightforward. Fourteen years from now, there will be eight billion people on the planet. At around the same time, India will overtake China as the most populous nation on earth. Most of the growth will occur in the world’s poorer countries. Proportionally, Europe’s population will decline, while Africa’s will increase.