NCPA - National Center for Policy Analysis


August 27, 2009

Many developed regions of the world have below-replacement fertility levels (less than 2.1 children per woman).   In many highly developed countries, the trend towards low fertility has also been deemed irreversible.  However, if Mikko Myrskyla of the University of Pennsylvania and his colleagues are correct, things might not be so bad.  A study they have just published in Nature suggests that as development continues, the demographic transition reverses itself.

Dr. Myrskyla looked at the world as it was in 1975 and as it is now (or, at least, as it was in 2005).  He compared two things:

  • One was the total fertility rate (the number of children that would be born to a woman in a particular country over the course of her life if she experienced the age-specific fertility rates observed in that country during the calendar year in question).
  • The other was the human development index for that country (the HDI, a measure used by the United Nations, has three components: life expectancy; average income per person; and level of education. Its maximum possible value is one).

What did the researchers find?

  • Back in the 1970s, no country got anywhere near one; of the 107 places the researchers looked at, the best was Canada, with an HDI of 0.89.
  • By 2005, however, things had improved markedly; two dozen of what were now 240 countries had HDIs above 0.9 -- and something else remarkable had happened.
  • Back in 1975, a graph plotting fertility rate against the HDI fell as the HDI rose; by 2005, though, the line had a kink in it.
  • Above an HDI of 0.9 or so, it turned up, producing what is known in the jargon as a "J-shaped" curve (even though it is the mirror image of a letter J).
  • In many countries with high levels of development (around 0.95) fertility rates are now approaching two children per woman (there are exceptions, notably Canada and Japan, but the trend is clear).

Dr. Myrskyla's data, however, suggest the ultimate outcome of development may not be a collapsing population at all but, rather, the environmentalist's nirvana of uncoerced zero population growth.

Source:  Editorial, "A link between wealth and breeding: The best of all possible worlds?" The Economist, August 6, 2009; based upon: Mikko Myrskyla et al., "Advanced in development reverse fertility declines," Nature, August 6, 2009.

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