National Geographic : 2011 Jan
mid-19th century on, sewers began to channel human waste away from drinking water, which was then ltered and chlorinated; that dramati- cally reduced the spread of cholera and typhus. Moreover in 1798, the same year that Malthus published his dyspeptic tract, his compatriot Edward Jenner described a vaccine for small- pox---the rst and most important in a series of vaccines and antibiotics that, along with bet- ter nutrition and sanitation, would double life expectancy in the industrializing countries, from 35 years to 77 today. It would take a cranky person to see that trend as gloomy: " e devel- opment of medical science was the straw that broke the camel's back," wrote Stanford popula- tion biologist Paul Ehrlich in 1968. Ehrlich's book, e Population Bomb, made him the most famous of modern Malthusians. In the 1970s, Ehrlich predicted, "hundreds of millions of people are going to starve to death," and it was too late to do anything about it. " e cancer of population growth...must be cut out," Ehrlich wrote, "by compulsion if voluntary meth- ods fail." e very future of the United States was at risk. In spite or perhaps because of such lan- guage, the book was a best seller, as Malthus's had been. And this time too the bomb proved a dud. e green revolution---a combination of high-yield seeds, irrigation, pesticides, and fer- tilizers that enabled grain production to double ---was already under way. Today many people are undernourished, but mass starvation is rare. Ehrlich was right, though, that population would surge as medical science spared many lives. A er World War II the developing coun- tries got a sudden transfusion of preventive care, with the help of institutions like the World Health Organization and UNICEF. Penicillin, the smallpox vaccine, DDT (which, though later controversial, saved millions from dy- ing of malaria)---all arrived at once. In India life expectancy went from 38 years in 1952 to 64 today; in China, from 41 to 73. Millions of people in developing countries who would have died in childhood survived to have chil- dren themselves. That's why the population explosion spread around the planet: because a great many people were saved from dying. And because, for a time, women kept giving birth at a high rate. In 18th-century Europe or early 20th-century Asia, when the average woman had six children, she was doing what it took to replace herself and her mate, because most of those children never reached adulthood. When child mortality declines, couples eventually have fewer children---but that transition usually takes a generation at the very least. Today in developed countries, an average of 2.1 births per woman would maintain a steady population; in the devel- oping world, "replacement fertility" is somewhat higher. In the time it takes for the birthrate to settle into that new balance with the death rate, population explodes. Demographers call this evolution the demo- graphic transition. All countries go through it in their own time. It's a hallmark of human prog- ress: In a country that has completed the transi- tion, people have wrested from nature at least some control over death and birth. e global population explosion is an inevitable side e ect, a huge one that some people are not sure our civilization can survive. But the growth rate was actually at its peak just as Ehrlich was sound- ing his alarm. By the early 1970s, fertility rates around the world had begun dropping faster When child mortality declines, couples eventu- ally have fewer children---but that transition takes a generation.