There are two ways to look at world population numbers.
By one measure, the world has grown beyond its capacity. As Hillary Rodham Clinton's science advisor, Nina V. Fedoroff, recently told the BBC: "The planet can't support many more people."
But in parts of Europe and other developed countries, the problem isn't too many people but too few: Dwindling birthrates have prompted concerns about whether a shrinking pool of young people will be able to maintain the social safety net for the previous generation.
Politically, the discussion about population is deeply polarized. Conservatives talk about falling birthrates in almost apocalyptic terms, suggesting Europe is being punished for its sins of secularism and feminism. Bestselling author Mark Steyn has predicted "the demise of European races too self-absorbed to breed," while 2008 Republican presidential candidate Mitt Romney warned that "Europe is facing demographic disaster." Liberals, meanwhile, tend to see the Malthusian specter of overpopulation as a far greater threat.
So who is right? Is our future endangered by overpopulation or underpopulation? The answer is both. But in an elegant irony, the two problems have the same solution: giving women more control over their fertility and their lives. Both very high birthrates and very low ones threaten social stability, and both, it turns out, are symptoms of countries' failures to meet women's needs.
Right now, the world's population is growing at the unsustainable rate of 78 million people a year, and according to the United Nations, it will probably keep growing at 70 million or 75 million a year through 2020. Almost all of that growth is in the slums of the Third World. As former CIA Director Michael V. Hayden said in a speech last year, "By mid-century, the best estimates point to a world population of more than 9 billion. That's a 40% to 45% increase -- striking enough -- but most of that growth is almost certain to occur in the countries least able to sustain it. Places where swelling population is likely to fuel instability and extremism -- not just in those areas but beyond them as well."
The ethical and effective way to counter rapid population growth is to bolster women's rights and improve their access to family planning. Education is crucial -- study after study has found that girls who go to school marry later and have fewer, healthier children. Access to contraception is also key. According to the Guttmacher Institute, almost a quarter of married women in sub-Saharan Africa have an unmet need for birth control. In a number of Latin American and African countries, more than 40% of recent births are said to be unwanted. Meanwhile, high rates of unsafe, illegal abortion -- responsible for 13% of maternal mortality globally, according to the World Health Organization -- speak to women's desperation to control their fertility.
At the same time, several developed countries, including Japan, Russia, Italy and Spain, have what appears to be the opposite problem. A stable population requires each woman to have an average of 2.1 children. (The extra tenth of a percent accounts for early deaths.) Demographers say that countries can adapt without much trouble to fertility that is a few tenths of a percent less than that. However, below about 1.7 children per woman, economic growth, pension systems and general cultural viability all come into question as a shrinking pool of young people is forced to support a growing number of the aged.
Italy, for example, has a fertility rate of 1.3 children per woman.
One leading demographer estimated that if Italy's 1995 birthrate remained stable over 100 years, then without immigration its population a century hence would be a mere 14% of what it is today.
That kind of population decline can't simply be remedied with immigration without causing major cultural upheavals and nationalist backlashes.
Some social conservatives are using the threat of rapid First World population decline to argue for restrictions on women's rights. But that gets it precisely backward. In developing countries, lower social status for women is associated with higher fertility, but once societies become highly industrialized and women taste a certain amount of freedom, the reverse is true.
Fertility is reaching dangerously low levels in countries where social attitudes and institutions haven't caught up with women's desire to combine work and family. When faced with men who are unwilling to share domestic burdens, inflexible workplaces and day-care shortages, many women respond by having fewer children or forgoing motherhood altogether.