The received wisdom among demographers and other social sciences is that as countries develop economically and socially their fertility rates decline. However, a recent article in Nature1 has shown that at higher levels of development, as measured by the UN’s Human Development Index (HDI), the fall in fertility goes into reverse. Could this be the answer to the problem of ageing populations?

Before answering this question, it is important to try and understand why this reversal of fertility has happened and whether it is likely to be permanent. The reversal is likely to have been due to a mixture of a number of socio-economic changes, for example: increased employment flexibility and conditions, especially for women, welfare provision and reforms, governments’ family policies and direct attempts to increase fertility. The authors tested whether the increase in fertility at higher HDI levels was due to a catch-up in fertility due to earlier delayed childbearing. However, this does not seem to have been the case. There may also have been the impact of immigrant fertility. Countries with higher HDI scores are among the countries with the largest immigrant populations. As immigrants tend to have higher fertility than the host country population then one would expect fertility to increase as the proportion of immigrants in society increases.

Not every country with a high HDI has seen its fertility increase. Most of these exceptions are Asian which may therefore imply certain cultural barriers to a change in fertility and also, in some cases, a lower immigrant population. However, a Western exception to the rule is Canada which is surprising and the authors have not been able to identify why this is the case.

What does this change imply for the future of populations in developed countries currently worrying about population ageing? Although fertility is shown to increase in most societies as they reach high HDI scores, it still does not return to replacement level. Therefore the population of these countries is still destined to decline unless immigration makes up the difference. However the decline may be slower than previously expected and the level of immigration required to make up for a lack of births could be lower than expected under current assumptions of a continuing fall in fertility as countries become more well off. While this may sound good for these developed countries it may reduce the opportunities for migrants from poorer countries to move to developed countries and improve their own livelihood and, through their remittances, help the societies they have left.

But what about the impact on climate change? To the extent that greenhouse gas emissions are related to levels of consumption and population, an increase in population in countries with higher levels of HDI, which to a very large extent reflects levels of material well being and consumption, means that the world will have to try even harder to reduce its emissions.

Will this reversal of fertility rates last? This depends very much on what the underlying causes of the change are. If the increased fertility is due to permanent socio-economic changes then it may well last. However, if it’s due to immigration then, as immigrant numbers reduce, so would the level of fertility.


1 Myrskyla M. et al. Advances in development reverse fertility declines. Nature 460, 741 – 734 (2009).

Dermot Grenham is chief actuary for the social security, demography and overseas pensions team of the Government’s Actuary Department in the UK. He has held various financial reporting...