Go forth and multiply a lot less, The Economist recommends:
Sometime in the next few years (if it hasn’t happened already) the world will reach a milestone: half of humanity will be having only enough children to replace itself. That is, the fertility rate of half the world will be 2.1 or below. This is the “replacement level of fertility”, the magic number that causes a country’s population to slow down and eventually to stabilise. According to the United Nations population division, 2.9 billion people out of a total of 6.5 billion were living in countries at or below this point in 2000–05. The number will rise to 3.4 billion out of 7 billion in the early 2010s and to over 50% in the middle of the next decade. The countries include not only Russia and Japan but Brazil, Indonesia, China and even south India.The move to replacement-level fertility is one of the most dramatic social changes in history. It manifested itself in the violent demonstrations by students against their clerical rulers in Iran this year. It almost certainly contributed to the rising numbers of middle-class voters who backed the incumbent governments of Indonesia and India. It shows up in rural Malaysia in richer, emptier villages surrounded by mechanised farms. And everywhere, it is changing traditional family life by enabling women to work and children to be educated. At a time when Malthusian alarms are ringing because of environmental pressures, falling fertility may even provide a measure of reassurance about global population trends.
So, why is 2.1 such a special number?
If there were no early deaths, the replacement rate would be 2.0 (actually, fractionally higher because fewer girls are born than boys). Two parents are replaced by two children. But a daughter may die before her childbearing years, so the figure has to allow for early mortality. Since child mortality is higher in poor countries, the replacement fertility rate is higher there, too. In rich countries it is about 2.1. In poor ones it can go over 3.0. The global average is 2.33. By about 2020, the global fertility rate will dip below the global replacement rate for the first time.
Population growth has quite a bit of momentum though:
Populations can rise while fertility declines because of inertia, which matters a lot in demography. If, because of high fertility in earlier generations, there is a bulge of women of childbearing years, more children will be born, though each mother is having fewer children. There will be more, smaller families. Assuming fertility falls at current rates, says the UN, the world’s population will rise from 6.8 billion to 9.2 billion in 2050, at which point it will stabilise (see chart 1).
Behind this is a staggering fertility decline. In the 1970s only 24 countries had fertility rates of 2.1 or less, all of them rich. Now there are over 70 such countries, and in every continent, including Africa. Between 1950 and 2000 the average fertility rate in developing countries fell by half from six to three — three fewer children in each family in just 50 years. Over the same period, Europe went from the peak of the baby boom to the depth of the baby bust and its fertility also fell by almost half, from 2.65 to 1.42 — but that was a decline of only 1.23 children. The fall in developing countries now is closer to what happened in Europe during 19th- and early 20th-century industrialisation. But what took place in Britain over 130 years (1800–1930) took place in South Korea over just 20 (1965–85).Things are moving even faster today. Fertility has dropped further in every South-East Asian country (except the Philippines) than it did in Japan. The rate in Bangladesh fell by half from six to three in only 20 years (1980 to 2000). The same decline took place in Mauritius in just ten (1963–73). Most sensational of all is the story from Iran.
When the clerical regime took over in 1979, the mullahs, apparently believing their flock should go forth and multiply, abolished the country’s family-planning system. Fertility rose, reaching seven in 1984. Yet by the 2006 census the average fertility rate had fallen to a mere 1.9, and just 1.5 in Tehran. From fertility that is almost as high as one can get to below replacement level in 22 years: social change can hardly happen faster. No wonder the explosion on the streets of Iran this year seemed like a clash between two worlds: 15–29 year-olds, one-third of the population, better educated and with different expectations, against the established regime and the traditionalists.
Why has fertility dropped? Imagine you were born a poor peasant, but now you find yourself living in the city:
You may have moved to a town, or your village may have grown. Schools, markets and factories are within reach. And suddenly, the incentives change. A tractor can gather the harvest better than children. Your wife may get a factory job — and now her lost wages must be set against the benefits of another baby. Education, thrift and a stake in the future become more important, and these middle-class virtues go hand in hand with smaller families. Education costs money, so you may not be able to afford a large family. Perhaps the state provides a pension and you no longer need children to look after you. And perhaps your wife is no longer willing to bear endless offspring. Higher living standards, better communications and more education enable you to rely on markets and public services, not just yourself and your family.
Macroeconomic research bears out this picture. Fertility starts to drop at an annual income per person of $1,000–2,000 and falls until it hits the replacement level at an income per head of $4,000–10,000 a year (see chart 2). This roughly tracks the passage from poverty to middle-income status and from an agrarian society to a modern one. Thereafter fertility continues at or below replacement until, for some, it turns up again (see article).The link between living standards and fertility exists within countries, too. India’s poorest state, Bihar, has a fertility rate of 4; richer Tamil Nadu and Kerala have rates below 2. Shanghai has had a fertility rate of less than 1.7 since 1975; in Guizhou, China’s poorest province, the rate is 2.2. So strong is the link between wealth and fertility that the few countries where fertility is not falling are those torn apart by war, such as Congo, Liberia and Sierra Leone, where living standards have not risen.
Family research adds detail to this sketch. Indonesia’s Family Life Survey showed that, on average, each birth reduced by a fifth the likelihood that a woman would have a job — lowering household income and pushing some families into poverty. So smaller families made middle-class status more likely. Between 1974 and 1996, Bangladesh turned a district called Matlab into a giant demographic experiment: some villages and households got family planning, others did not. According to one study of the results, fertility in the areas that received help declined by around 15% more than in those that did not. And over the two decades of the experiment, indicators of the well-being of women and their children — health, earnings, household assets and so on — were all higher in the villages that got the planning. Does this suggest that lower fertility causes wealth, or that wealth lowers fertility? It would be better to say that the two things go together.
Higher standards of living reduce fertility, and lower fertility improves living standards — in a modern economy.