Population growth also worsens human strife. Several recent studies have shown that a key predictor of armed civil conflict in developing nations is not their predominant religion or the region in which they are located, but the fraction of the adult population between the ages of 15 and 29.
Rapidly growing countries are flooded with unemployed and disenfranchised young men. Far too often, they become prime fodder for crime or war, or even recruitment into a terrorist cell.
Gunnar Heinsohn, an expert in genocide research at the University of Bremen, Germany, argues, for example, that a critical difference between two Muslim countries, war-torn Afghanistan and peaceful Tunisia, is that Afghanistan's birth rate is four times as high. Throw as many soldiers and dollars at Afghanistan as you like, he suggests, but the country will be roiled by conflict until its mushrooming population stabilises.
Finally there is the politically charged issue of immigration. According to the United Nations Population Division, the US population will swell by well over 100 million people by the year 2050, largely because of the millions of Latin American immigrants it receives each year.
Rapidly growing countries are flooded with unemployed and disenfranchised young men.
Western Europe faces similar pressures but with the complication that many of its immigrants are Muslims from north Africa, the Middle East and south Asia: they do not always assimilate as easily into western societies as many Latin Americans. Immigrants contribute positively in diverse ways, but large numbers can also exacerbate economic, environmental and social pressures.
Fortunately, rapid population growth is soluble. There is a simple means to slow it: educate women, especially about their reproductive health. On average, better-educated women defer having children until their early 20s. They have fewer children overall and fewer unwanted pregnancies. More of their children survive, and they are healthier and better educated in their turn. The women and their families are also much better off economically.
Giving women the option of contraception is the single most important factor in achieving the "demographic transition" in which a nation's population growth slows, longevity increases, and it starts to balance its numbers of young and older people.
It's hard to say whether the upper echelons of conservative faiths will ever stop condemning contraception. But it's certain that with a different leadership, the US could become part of the family-planning solution, rather than part of the problem. Before the next US presidential election, the candidates should say where they stand on family-planning issues - and US citizens should remember this when they vote.
William Laurance is a biologist at the Smithsonian Tropical Research Institute in Balboa, Panama.
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Published on 30 October 2007
