November 5, 2012
to be posted on

Henry C. Harpending
Department of Anthropology
270 S. 1400 East Room 102
University of Utah
Salt Lake City, UT 84112-0060

Dear Dr. Harpending:

Yes, it’s I again.  I wrote in March about how fertility depends upon consanguinity, and I have little to offer that I did not mention then. 

But a good friend has brought to my attention that you took an interest in the work of Emmanuel Milot and colleagues published in Proceedings of the National Academy of Sciences in which the steady rise in fertility (Actually it was age of first child as a proxy for fertility; I don’t know why they couldn’t have used fertility itself, as they had the data.) in the island of Ile aux Coudres in Quebec between 1800 and 1940.  This was touted as being an example of human evolution.

Hmm.  The classical example of evolution happening under our noses is “industrial melanism” in England during the heyday of coal in the Industrial Revolution.  Soot made the trees black and moths got darker, presumably the better to hide from predators, and when the air pollution cleared up the moths got lighter again.

Well it seems reasonable.  I should not be surprised if there was an actual genetic mutation that made the darkening possible.  That’s evolution for sure.  I would, until instructed otherwise, attribute the subsequent lightening to atavism, which is seems to me distinct from evolution.

If all you need to have evolution is a change in gene frequency under selective pressure, the history of Haiti might provide such an example.  As it was presented to me, when the slaves rebelled they killed all the white people and then all the mulattoes.  I’m skeptical.  I imagine many people escaped to the east side of Hispaniola.  But there seems to have been a change in gene frequency.

The study concluded that the change in fertility occurred because the environment was good for having lots of children.  Really?  Evolution always gives the advantage to those with more children and grandchildren.  It’s the definition of fitness.   

But they did not consider consanguinity.  Nobody ever seems to.

The time scale seems far too abrupt for real evolution, that is the introduction of new genes adapted to a change in the environment.  But it is an excellent time scale for epigenetic effects, which probably mediate the relationship between consanguinity and fertility.

The population of the island at the end of the study was 1,600 which is probably over twice the size of a population that can endure the loss of consanguinity, but it is easy to image that an island of ten or fifteen square miles could have a few fairly isolated lineages.  None the less I would expect that fertility declined after the study period ended. 

I just thought you might be interested.


M. Linton Herbert MD 

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