Population growth is no longer a clear-cut problem, reports Harriet Swain Peter McDonald (below) says the issue is how we will balance the world's labour supply

This is World Population Week, promoted by the United States-based Population Institute to draw attention to the "four horsemen of the 21st-century apocalypse: overpopulation, deforestation, water scarcity and famine". Tuesday was the day, according to the United Nations, when the world's population reached six billion, double the number 40 years ago. Alarming visions of how our apparently overcrowded world is to accommodate all these extra people - five billion more than there were in 1800 - have prompted warnings of imminent disaster.

But all is not quite what it seems. First, fertility is declining. Estimates for the world population in 2050 are about 8.9 billion, rather than the 9.4 billion predicted just three years ago. And while the West regards population decline as desirable for developing countries, it sees it as a problem in its own. Although some praise countries such as China for its effective control of population growth, others attack human rights abuses carried out in the name of population control and argue that moderate population growth carries material and social benefits.

Two centuries ago, Thomas Malthus plotted population growth against resources and warned that resources were not enough; either natural or "moral" disasters, such as abortion, would have to keep population in check. But it is clear that population is not just about matching numbers.

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At the last ten-yearly conference held by the United Nations Population Fund in Cairo in 1994, countries agreed that total fertility rates should be less significant than rates of family education, literacy and standards of reproductive and sexual health. The message was that individuals, particularly women, should be free to decide how many children they want to have, and have the information and ability to be able to do so. This approach is harder than simple family planning because it involves coordinating different agencies, some more willing than others.

But more sophisticated approaches are needed, as fear of fertility ceases to dominate.

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Kathleen Kiernan, reader in social policy and demography at the London School of Economics, says the reason for falling fertility is education and "empowerment" of women. There is clear evidence that the higher the levels of education for women, the lower the fertility rate tends to be.

It is not straightforward. In some cultures, educated women still like to have large numbers of children, both as proof of prosperity and as security for old age. According to Kiernan, wealthier women in the West are also more likely than poorer women to have children, while no link has been found between female employment and fertility.

Nor are children the only focus. Ageing, a growing issue in the developed world, is now affecting developing countries, where life expectancy has increased.

The difficulties ageing raises are accentuated by HIV and Aids, which, according to a recent UNFPA report, have reduced long-term population projections by about a third. Many of those affected by the two conditions are of working age, which forces old people to support sick children whom they once expected would support them. Many are also professional and educated people; replacing their skills becomes an additional expense.

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Added to these issues are changing family patterns. Family breakdown, cohabitation and teenage pregnancy all have an impact on population. But the study of population does not carry the sense of doom it once did. John Hobcraft, professor of population studies at the LSE, says: "There clearly are still people around who see population as the problem. But I think it is a much smaller group of people than it used to be."