The population of some wealthy countries is shrinking because of a declining birth rate. It comes as a surprise, and one with policy implications, that after a certain point of development that trend can reverse.
In many industrialized nations, including Japan, South Korea, Germany and Italy, and much of southern and eastern Europe, fertility is far below replacement — the level at which enough children are born to replace their parents. Many of these countries do not accept (or want) immigrants to make up this deficit, so their populations are projected to decline over the next 25–50 years, with potentially scary consequences1. Low fertility means that women delay and reduce childbearing2, choices that typically follow improvements in education, wealth and health. Widespread fertility decline and its associated problems have seemed inevitable. But on page 741 of this issue3, Myrskylä, Kohler and Billari brighten this prospect by presenting evidence that such declines may be expected to reverse.
For many years, environmental concerns have been used to argue that it would be a good thing if human populations became smaller. If that's true, should we not welcome low fertility and population decline wherever it occurs? The difficulty with this view is that although smaller populations may indeed be desirable in the long term, in the short term population decline poses challenges that we do not know how to manage. Low fertility means fewer babies, and eventually a smaller workforce that would have to pay higher per capita costs of infrastructure and social support systems. A consequence of low fertility and long lives is an ageing population with its attendant social and economic effects. National economic output would probably decline along with the size of the workforce. Political and military capability and influence would decline along with population. Thus, for many rich countries, population decline is a serious concern.
Myrskylä et al.3 examine the relationship between fertility and the human development index (HDI), a measure of education, income and lifespan4. Fertility decreases with increasing HDI during early stages of development. But at high levels of development, fertility in many countries increases with HDI. This is the first evidence that fertility levels might move back towards the replacement level in such countries as Italy, Spain, the Netherlands, Germany and Sweden. Perhaps babies will be 'in' again in the richest countries.
To understand the fuss about low fertility and population decline, consider how fertility affects population number. Annual fertility is measured as birth rate expected according to a woman's age, and it is summarized by the total fertility rate (TFR), the total number of children a woman could have at those age-specific rates. Replacement fertility in countries with long life expectancies is at a TFR of about 2.1. Many rich countries now have fertilities far below this replacement level, close to the record low fertilities of Spain, Japan and Italy, which had TFRs close to 1.3 in 2005. If fertility stayed at that level, the populations of these countries would eventually decline at about 1.5% per year. Annual immigration at that amount would just offset the decline, but would also lead to a rapid increase in the number of foreign-born residents. The latter factor comes with political concerns about the economic, social and cultural assimilation of immigrants, concerns that remain even in the United States, a country with a long history of immigration at or near such levels.
To obtain the HDI, education, income and length of life are evaluated relative to best-possible values and combined into a score on a scale of 0 to 1. Most low-fertility countries, including Spain and Italy, had HDI levels of more than 0.9 in 2005; more broadly, the HDI in most countries has been increasing over time. Myrskylä et al. discovered that in virtually all countries, the TFR falls as the HDI increases up to about 0.86. By contrast, when the HDI rises above that level, the TFR increases in many (but not all) countries.
The authors argue that high HDI levels (above 0.86) may result in changes that benefit women and make it easier for them to choose to have children. Increases in development in rich countries come about as a result of higher educational attainment for women, increases in the percentage of women in the labour force, and an increase in women's incomes. These changes make it likely that women, and couples, will find it easier to pay the high economic price of having children. In addition, women with more skills and work experience — important elements of what we call human capital — will probably find it easier to move out of jobs to have children and then to move back into jobs once the children are in school.
How far can these results go in alleviating concerns over population decline? An increase of 0.01 in the HDI can increase the TFR by 0.03 or more3, or equivalently can increase the eventual annual growth rate by about 0.06%. This may seem like considerable leverage. But the HDI can't go above 1, and many low-fertility countries already have HDI levels of around 0.93. Therefore, the best one can expect is an increase in TFR of 0.2, which is equivalent to raising the growth rate by about 0.4% from its currently projected lows. Countries such as Spain or Italy would still be below replacement, although, setting the social and political considerations to one side, they would be able to maintain their populations with far fewer immigrants.
Myrskylä and colleagues3 find important exceptions to the relationship between the TFR and HDI — in some countries, including Japan, South Korea and Canada, the TFR continued to fall even when the HDI rose above 0.86. What might be happening here? The authors suggest that the positive effects of increasing HDI on women's decisions to have children may not apply in Asian countries because of social or cultural characteristics. Perhaps so, but what about Canada? These puzzling findings may instead be due to use of the HDI, which does not directly tell us which aspects of human development affect women rather than men. A different measure, the gender development index (GDI)4, describes the difference between male and female development. It would be useful to examine the relationship between the TFR and GDI, and to ask if countries such as Japan or Canada have a noticeable difference between trends in the HDI and GDI.
A final point worth stressing is that Myrskylä and colleagues3 also show that fertility in developing countries, which have HDI levels much below 0.86, falls with increasing development. The social and environmental challenges of burgeoning populations in many developing countries, such as Bangladesh, Egypt, India and Pakistan, can only be addressed if these countries achieve and maintain low, below-replacement, fertility. Even in China, where low fertility was achieved by fiat, the maintenance of low fertility must eventually be driven by individual choice. In these and other developing countries, increased human development, especially development that benefits women, is still the most powerful and most democratic route to achieving and maintaining lower populations.
United Nations Population Division. Replacement Migration: Is it a Solution to Declining and Ageing Populations? (United Nations, 2002).
Lesthaeghe, R. & Willems, P. Pop. Dev. Rev. 25, 211–228 (1999).
Myrskylä, M., Kohler, H.-P. & Billari, F. C. Nature 460, 741–743 (2009).
United Nations Development Programme. Statistics of the Human Development Report http://hdr.undp.org/en/statistics/indices (2008).
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Economy and Society (2016)