December 19, 2011

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NY, NY 10019
You suggest (Miracle or Malthus ECONOMIST vol. 401 no. 8764 December 17, 2011 page 81 that sub-Saharan Africa has a birth rate that is falling, but falling much slower than it has fallen elsewhere.  The “demographic dividend,” rapid economic growth produced in part by having a large proportion of the population being young, productive adults as fertility falls, might be less pronounced but more prolonged than in places where fertility fell faster. 

You account for the slow fall with cultural expectation, relatively unavailable, contraception, weak political will, and lack of education for women.  But you left one thing out.  A study done in Iceland compared kinship with fertility.  A. Helgason et al., Science 319 813 (2008) You reviewed it under the misleading title, “Kissing cousins.  Missing children.”    They found that marrying roughly third or fourth cousins produced the highest number of children and grandchildren.  Out past about seventh cousins fertility fell to below replacement, this in Iceland, where the factors you mention have been optimized. 

The insistent implication is that in Africa people have not adopted the marry-no-cousin mating strategy so prevalent elsewhere.  Until they do, they will probably not fall to replacement.  The sanguine UN projection of the birth rate in the developed world stabilizing at replacement level flies in the face of the fact that once fertility drops below replacement, age at first marriage immediately starts getting older.  That cannot go on forever. 

It is nice to think there will still be people.  Wish Africa luck.


M. Linton Herbert MD 

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