July 12, 2013
to be posted on nobabies.net

Ruth Mace
Department of Anthropology
University College London
London WC1E 6BT

Dear Ruth Mace:
I read your warm spirited article (Ruth Mace The Cost of Children NATURE vol. 499 no. 7456 July 4, 2013 page 32) with a sense we share interests.  We are both interested in the decline in the number of children being born, which at its logical extreme of course must go far beyond the experience of going weeks at a time without properly interacting with children.  Of the factors you consider might be at work I take it that economic factors appear to be predominant.  By as you say, “One cannot rule out the effects of factors that have not been tested for.”  You conclude that the demographers have passed the baton to evolutionary anthropologists who have seized it and run.

Alas, were that true.  From my perspective the baton appears to lie on the track all neglected and motionless.  But it is within reach.  There is unquestionably a biological component influencing how many children a couple has.  (An Association between Kinship and Fertility of Human Couples Agnar Helgason et al. SCIENCE vol. 329 no. 5864 February 8, 2008 page 813 – 816)  By and large less kinship means less fertility.  That oversimplifies but not much.  If you look at the article you may decide that the effect is small in any one generation but also you will see that the effect accumulates over generations. 

If you should wish to see more, I suggest this link.  http://nobabies.net/A%20December%20summary.html
If you find it forbidding I am at your service to explain, summarize, hedge or whatever you like.  I have been raising some fruit flies in pursuit of the principle and attach a copy.  Although I am sure my fruit flies are as fiscally prudent and as well educated as any fruit flies, that isn’t saying much.  They respond to the same biological clues that humans respond to and it just about has to be for the same reasons.  In fact at this point in time I am unconvinced that there is anything BUT kinship, measured over generations, that has a significant effect on fertility. 

Education seems to you to be less important than economic considerations, but it might be easier to get a hold of it.  The inverse correlation between education and fertility is well known, but nobody to my satisfaction has sorted out just which lessons count.  I rather suspect that girls are going to schools where they learn things that would make us cringe, yet their fertility is affected just as it would be had they matriculated where either of us did. 

Oversimplifying it a bit, girls in school do as they are told and make good grades while boys clown and fight.  At least I did.  But both do something that isn’t on the curriculum.  They fall in love.  And since school introduces them to strangers they are more likely to marry strangers.  That means fewer children.  This notion, of course, is subject to test.  Work out mating patterns in places where the birth rate is falling and check to see whether education or income has any effect on fertility after mating has been accounted for.  That has been done in Denmark (Human Fertility Increases with marital radius. Rodrigo Labouriau and António Amorim.  GENETICS volume 178 January 2008 page 603 and Comment on “An Association Between the Kinship and Fertility of Human Couples,” Rodrigo Labouriau and António Amorim SCIENCE vol. 322, page 1634b December 12, 2008) and in both cases the answer was absolutely not. 

There is the baton. 

Let me know what you think.


M. Linton Herbert MD 

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