This blog is intended to go along with Population: An Introduction to Concepts and Issues, by John R. Weeks, published by Cengage Learning. The latest edition is the 12th (it came out in 2015), but this blog is meant to complement any edition of the book by showing the way in which demographic issues are regularly in the news.

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Wednesday, September 5, 2012

Does Human Fertility Square With Evolutionary Theory?

The connection between demography and evolutionary theory is a tight one in that Darwin acknowledged that his early thinking was inspired by reading Malthus. But, are we humans very good at evolution? This question was raised in an article just published online (although not yet accessible to most of us) in the Proceedings of the Royal Society B: Biological Sciences, with Anna Goodman of the London School of Hygiene and Tropical Medicine as the lead author. This week's Economist was one of several news outlets that picked up on the story.
Why the demographic transition happens, though, is obscure—for this reaction by Homo sapiens to abundance looks biologically bonkers. Other species, when their circumstances improve, react by raising their reproductive rate, not curtailing it. And work just published by Anna Goodman of the London School of Hygiene and Tropical Medicine and her colleagues, in the Proceedings of the Royal Society, suggests what humans do is indeed bananas. Dr Goodman has shown that the leading explanation advanced by biologists for the transition does not, in the context of the modern world, actually deliver the goods.
This explanation is that, according to circumstances, people switch between two reproductive strategies. One, known to ecologists as “r-selection”, is to produce lots of offspring but invest little in each of them. This works in environments with high infant mortality. The other, known as “K-selection”, is to have only a few offspring but to nurture them so that they are superb specimens and will thus do well in the competition for resources and mates, and produce more grandchildren for their parents than their less well-nurtured contemporaries. The demographic transition, according to this analysis, is a shift from r-type to K-type behaviour.
My reaction to this is, of course, that biologists may not understand why the demographic transition occurs, but we social scientists do understand it. As far as we know, humans are the only species able to effectively control their own mortality and fertility levels. This happened mostly after Darwin died, of course, so we can't necessarily blame him for the fact that subsequent biologists want to impose the exact same models on humans that they find working in other animals. The article has drawn a lot of on-line comments and my sense is that most readers get it, even if the author of the Economist article (and perhaps of the Royal Proceedings article) did not.


  1. Through the ages, the number of children has depended on everything from mere survival of the family line, to religious beliefs, to the undying expectation of a boy after the 8th girl is born. Since the health practices have improved, resulting in declining death rates, number of child births in various countries has depended more on regional ideology and attitudes than on the need to continue the family genes. I think the differences in ideologies, cultural practices, and development stages of various countries are much better suited explanations for the demographic transitions. They can explain the youth bulge in India and the growing elderly population in Japan.

  2. Most humans are well aware and in control of their reproductive abilities. Over the last several decades this choice of having more children or not has become more evident, especially in developing countries, which was a long awaited movement. Humans all over the globe have varying cultural and ideological beliefs, but they are still considered to take part in the demographic transitions that influence their choices due to human instinct. The only "shift' that is taking place is that people are finally starting to realize that our globe cannot provide for families of 6, so now its time to downsize!