Five years ago, a curious paper appeared in Nature. It acknowledged something that has become screamingly obvious: the collapse in the birth rate of the world’s most advanced countries which followed the introduction of the Pill is beginning to reverse itself. This is something I have been expecting for thirty years. Below is the letter I wrote to Nature in 2009.



 The recent uptick in fertility in many developed countries, which Myrskylä et al (Nature 460, 741-743; 2009) attribute to the Human Development Index passing a critical threshold, has a simpler explanation.

Circa 1970, the birth rate dropped abruptly in the countries cited as the Pill became widely available. That created a novel evolutionary situation. Until then, it was irrelevant to evolution whether a woman became pregnant because she wanted a child, or just because she had sex, as long as the maternal instinct got switched on at birth. Post-1970, however, women who actually desire children have been strongly selected for: unless it is unlike almost every other human characteristic, the desire for children will be largely under genetic control.

 Consider two women who in pre-Pill days would each have had 4 children, the first woman because she actively wanted a large family, the second just as an accepted consequence of marriage. Post-Pill, the first woman still has 4 children, who tend to inherit their mother’s desire for many offspring: the second caps her family at a much smaller number, who inherit their mother’s desire for few. Of course there are more extreme cases, including women who use contraception to ensure they have no babies at all. In a very few generations, the willingness to use contraception to limit family size will be effectively bred out of the population.

 Exactly one generation post-Pill, the birth rate indeed started to creep up again. If my hypothesis is correct, it will continue to increase rapidly, far ahead of any HDI-related prediction, approaching pre-Pill levels around 2050. This makes all variants of the UN population projections at http://esa.un.org/unpp/ grossly unrealistic: they are fallacious to the same degree as ignoring the anthropogenic greenhouse effect in climate prediction. Our future planning is grossly in error. Very soon, the problems of runaway population growth foreseen by Malthus will return to haunt us.


I was far from the first or the last person to make a similar point. But the letter was ignored, after a delay long enough to make it seem likely it had been referred back to the paper’s authors, who have continued to advocate purely economic causes.

Last year, the argument was fortunately revived in New Scientist’s letter pages. I will be blogging more about this in due course.



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