It is not hard to understand how most of us form the impression that overpopulation is one of the world's most pressing problems. Turn on your television and you see asylum-seekers slipping across border fences, or throngs of youths throwing stones somewhere in the Middle East. We hear of child soldiers in Africa, the disappearing rainforests of Brazil and melting polar ice caps - all caused by a human population that has nearly doubled in the past 40 years. We shake our heads when we read that, every year, the earth gains another 75 million human beings while losing approximately 27,000 plant or animal species.
Yet, beneath the surface of events, something else is happening. Though world population is still rising, it is doing so at barely half the rate of the late 1960s, and is now heading, many demographers believe, for absolute decline. The United Nations Population Division estimates that the number of infants and toddlers in the world (ages 0-4) will begin to contract within little more than ten years. The number of children under 15 will begin to decrease in little more than 20 years. This means, strange as it may sound, that all subsequent population growth will be due to increases in the numbers who survive to older ages. By 2050, there will be 35 million fewer children in the world than today, and 1.2 billion more people aged over 60.
Demographers at the International Institute for Applied Systems Analysis in Austria predict that total population will reach nine billion, mostly greying souls, by 2070 and then start to contract with compounding force. Long before then, many nations will shrink in absolute size, and the average age of the world's citizens will shoot up dramatically.
The new demographic currents in the world get stranger. During the second half of the 20th century, the median age in the UK increased by little more than three years, to 37.7. During the first half of the 21st century, according to UN forecasts, it will increase another 6.1 years. Yet this is nothing compared to the hyperageing occurring in Iran. There, before mid-century, the median age will increase by 20 years, according to UN projections, leaving more than half the population aged over 40.
Virtually anywhere one looks in the developing world - Egypt, Iraq, Mexico - the pattern is the same. Today, televised images from China show hordes of humanity crammed into tenements or camped out in railroad stations. Yet China's working-aged population will begin to shrink within ten years. By mid-century, 30 per cent of China's population will be aged over 60, and its total population could easily be less than it was in 1980. Even Africa is ageing at nearly double the rate of the US, and during the remainder of this century it will likely grow older than Europe is today.
Countries such as Italy and Japan at least got a chance to grow rich before they grew old. Most developing countries are growing old before they get rich.
Why is this happening? The primary reason is a dramatic fall in birth rates that began in western Europe in the 1930s and is now spreading to every corner of the globe. Since the start of the 1970s, while fertility rates were falling by 27 per cent in the industrialised countries, they were plummeting by 46 per cent in what the UN terms "less developed nations". The average woman in the world now bears just 2.69 children, down from more than 4.48 in 1970. That change is sufficient to cause rapid ageing of the population, particularly in regions where fertility has fallen most dramatically, such as the Middle East. If fertility rates continue to fall, as nearly all demographers believe they will, global population decline becomes almost inevitable.
It is easy to explain why children have become scarce in developed countries. In today's advanced economies, many people are not even done with school, much less established in a career, before their fertility (or their partner's) begins to decline. Then there is the rising cost of raising children. A recent survey found that parents in Britain spend on average £164,000 on each child, including the cost of university. As women have gained new economic opportunities, the costs in the form of foregone wages and compromised careers can often be even higher. Meanwhile, although social security systems around the world, as well as private pension plans, depend critically on the human capital created by parents, they offer the same pension benefits, and often more, to those who avoid the burdens of raising a family.
Now the developing world is experiencing the same demographic transition, only at a far faster pace. With the rapid growth of megacities, half the world's population now lives in urban areas, where children offer little or no economic benefit to their parents. And like their counterparts in the industrialised world, women in the third world increasingly take jobs, if only in sweatshops, and so they, too, may lose income when they bear children.
What also seems to have a dramatic effect is the availability of television. Since 1975, for example, Brazil's fertility rate has dropped by nearly half to just 2.27 children per woman. This is not the result of a family planning programme, since Brazil has never adopted one. Instead, studies show that births have declined from one region to the next coincident with the introduction of television. Today, the number of hours that a Brazilian woman spends watching telenovelas (domestically produced soap operas) strongly predicts how many children she will have. These soaps, though rarely addressing reproductive issues directly, typically depict wealthy individuals living the high life in big cities. The men are dashing, lustful, power-hungry and unattached. The women are lithesome, manipulative, independent and in control of their own bodies. The few who have young children delegate their care to nannies.
The telenovelas thus reinforce a cultural message that is conveyed as well by many North American and western European cultural exports: that people with wealth and sophistication are people who have at most one or two children. How much television affects birth rates through such messages, and how much it does so simply by changing how men and women spend their bedtime hours, we can only speculate. The US baby boom ended the year Johnny Carson, the late-night talk show host, took to the airwaves and began attracting millions of viewers.
Some of the global fall in fertility is also no doubt a response to falling infant mortality, which means that parents don't "need" as many children to achieve their ideal family size. Yet in many parts of the world, what with Aids, war, urban pollution and other sources of premature death, larger families are still necessary to avoid population loss. For example, in the developed world, the average woman must have about 2.1 children over her lifetime in order to replace the population, yet in war-torn Sierra Leone, 3.43 are needed. For the world as a whole, an average family size of 2.1 would lead to a 10 per cent loss of global population per generation, given current mortality rates. The spread of Aids in countries such as India could easily make these losses still more extreme. Women who are HIV-positive suffer a dramatic decline in their ability to bear children, which is having an even more profound effect on population than the number of deaths caused by Aids.
At first, slower population growth, and the population ageing that goes with it, seems beneficial. Many economists believe that falling birth rates helped make possible the economic boom that occurred first in Japan, and then in many other Asian nations, beginning in the 1960s. As the relative number of children declined, so did the burden of their dependency, thereby freeing up more resources for investment and adult consumption. The fall in Irish fertility rates, after birth control was legalised in 1979, produced a similar economic upturn. Today, China's rapid industrialisation is also aided by a dramatic decline in the proportion of dependent children in the population.
Over the next decade, the Middle East could benefit from a similar "demographic dividend". In every single country of that region, birth rates fell during the 1990s, often dramatically. The resulting "middle ageing" of the Middle East will ease the overall dependency ratio over the next ten to 20 years, freeing more resources for infrastructure and industrial development. With young adults accounting for a declining share of the population, the appeal of radicalism may also diminish, as Middle Eastern societies become increasingly dominated by middle-aged people concerned with such practical issues as healthcare and retirement savings. Just as population ageing in Europe in the 1990s was accompanied by the decline of the Red Brigades, the Red Army Faction and the IRA, falling birth rates in the Middle East could produce societies far less prone to political violence.
Yet even if declining fertility rates bring a "demographic dividend", that dividend eventually has to be repaid if the trend continues. At first there are fewer children to feed, clothe and educate, leaving more for adults to enjoy. But soon enough there are fewer productive workers as well, while there are also more and more dependent elderly, each of whom consumes far more resources than a child does. Even after considering the cost of education, a typical child in the US consumes 28 per cent less than the typical working-age adult, while elders consume 27 per cent more, mostly in health-related expenses.
The pandemic of obesity in the US and Europe, as well as the spread of sedentary lifestyles, threaten to create a new generation of elders that will be more prone to chronic disease and disability, and more costly to support. Already, annual gains in life expectancy among the elderly in the US are a fraction of what they were in the 1970s, presumably because of the increasingly lethal American lifestyle. Researchers estimate that obesity will cause a 10-20 per cent increase in the demand for nursing homes over what would otherwise occur from mere population ageing, and a 10-15 per cent increase in the cost of Medicare.
This dynamic suggests one of the many ways in which population ageing may become a vicious cycle. As the cost of supporting the elderly has risen, governments have already responded by raising taxes on younger workers, and will be compelled to do so much more often in the future. Younger workers, finding not only that the economy requires them to have far higher levels of education than were demanded of their parents, but that they must also pay higher taxes, will become less able to afford children, thus causing a new cycle of population ageing.
So where will the children of the future come from? Some biologists speculate that modern human beings have created an environment in which the "fittest", or most successful, individuals are precisely those who have few, if any, offspring. As more and more humans find themselves living under conditions in which children, far from providing economic benefit, have become costly impediments to success, those who are well adapted to this new environment will tend not to reproduce themselves. And many others who are not so successful will imitate them.
But this hardly implies extinction. Some people will still have children. They just won't be people highly motivated by material concerns or secular values. Disproportionately, the parents of the future will be people who are at odds with the modern environment - people who either "don't get" the new rules of the game that make large families a liability or who, out of religious or chauvinistic conviction, reject the game altogether.
Today, there is a strong correlation between religious conviction and high fertility. Compare, for example, the US - where as many as 84 per cent believe that Jesus was God or the Son of God - with the far more secular UK. The US fertility rate, which is the highest in the developed world, is 31 per cent greater than the UK's. Within the US, the pattern is the same. Fully 47 per cent of people who attend church weekly say that their ideal family size is three or more children, compared to only 27 per cent of those who seldom attend church. In Utah, where 69 per cent of all residents are registered members of the Church of Jesus Christ of Latter-Day Saints, fertility rates are the highest in the nation. Utah annually produces 90 children for every 1,000 women of childbearing age, while Vermont - the only state to send a socialist to Congress and the first to embrace gay unions - produces only 49.
So does the future belong to those who believe they are commanded by a higher power to procreate? On current trends, the answer appears to be yes. Once, demographers believed that some law of human nature would prevent fertility rates from remaining below replacement levels within any healthy population for more than brief periods. After all, don't we all carry the genes of our neolithic ancestors, who one way or another managed to produce enough babies to sustain the race? Yet today we can see that no law of nature ensures that human beings, living in free and developed societies, will create enough children to reproduce themselves. Japanese fertility rates have been below replacement levels since the mid-1950s, while the last time Europeans produced enough children to reproduce themselves was the mid-1970s.
Current demographic trends work against modernity in another way as well. Not only is the spread of urbanisation and industrialisation a major cause of falling fertility, it is a major cause of so-called "diseases of affluence", such as overeating, lack of exercise and substance abuse, which leave an ever higher percentage of the population stricken by chronic conditions. Those who reject modernity would thus seem to have an evolutionary advantage, whether they are clean-living Mormons, or Muslims who remain committed to comparatively large families, or members of emerging sects and national movements that combine pro-natalism with anti-materialism.
How can secular societies avoid population loss and decline? The problem is not that most people in these societies have lost interest in children. In every European nation, according to surveys, women in their forties intended to produce more children than they did. Indeed, if they had produced their ideal number of children, the continent would face no prospect of population loss.
The problem rather is that, even as modern societies demand more and more investment in human capital, this demand threatens its own supply. The clear tendency of economic development is towards a more knowledge-based, networked economy, in which decision-making and responsibility are increasingly necessary. So children often remain economically dependent on their parents well into their own childbearing years because it takes that long to acquire the panoply of technical skills, credentials, social understanding and personal maturity that jobs increasingly now require.
For the same reason, many couples discover that, by the time they feel they can afford children, they can no longer produce them, or must settle for just one or two.
Meanwhile, even as ageing societies become increasingly dependent on the human capital that parents provide, parents themselves get to keep less and less of the wealth they create by investing in their children. Employers make use of the skills parents endow in their children, but offer parents no compensation. Governments also depend on parental investment to provide the next generation of taxpayers but, with rare exceptions, give parents no greater benefits in old age than non-parents.
What can be done? Clearly, secular societies need to rethink how they go about educating young adults and integrating them into the workforce, so that tensions between work and family are reduced. Education should be a lifetime pursuit, rather than crammed into the prime reproductive years. There should also be many more opportunities for part-time and flexitime employment, and such work should offer full pension benefits, as well as meaningful career paths.
Governments should also relieve parents of having to pay into social security systems. By raising and educating their children, parents have already contributed hugely to these systems by providing essential human capital. Requiring parents to contribute payroll taxes as well is not only unfair, but also imprudent for societies that are already consuming more human capital than they produce.
In his 1968 bestseller, The Population Bomb, Paul R Ehrlich warned: "The battle to feed all of humanity is over. In the 1970s the world will undergo famines - hundreds of millions of people are going to starve to death in spite of any crash programmes embarked upon now." Fortunately, Ehrlich's prediction proved wrong, perhaps in part because so many people believed it would come true. But having averted the perils of overpopulation, the world now faces the unexpected challenge of population ageing and decline. We are in many ways blessed to have this problem instead of its opposite, but a problem it still is.
Phillip Longman is a Bernard L Schwartz Senior Fellow at the New America Foundation in Washington, DC and the author of The Empty Cradle: how falling birth rates threaten global prosperity and what to do about it (Perseus)