This is an open letter to Patrick Gerland. I have attempted to place it on his own blog.
January 28, 2014

Patrick Gerland
Dear Dr. Gerland:
A friend pointed out to me your recent interview with Charlotte McDonald of the BBC.  ( I have been obsessed with birth rates, consanguinity and violence for several years.  Any expert opinion is always treasured, and I find all of your points quite sensible.  However there is an issue nobody seems quite to get.  You attribute the difference between the high birth rate in turbulent Iraq and the low birth rate in tranquil Iran to better relevant education in the latter.  However a study done in Denmark showed that once issues of gene pool size and consanguinity were accounted for (they looked at the distance between the birthplaces of a couple and the size of the town they lived in) there was no effect on fertility by education or income.  Fertility depends on relatedness of the parents and of their ancestors and nothing else.  Let me (cough, cough) emphasize that: AND NOTHING ELSE.  A study done in Iceland showed kinship responding to consanguinity in the first and second generations with 90% error bars so tight that again babies are predicted by kinship AND NOTHING ELSE. 

I spare you the references.  If you are curious at all I strongly suggest you look at a recent summary I posted on my own web site: ( Given your interest in such matters I think it is well worth a read.  The effect accumulates over multiple generations, but except for intense inbreeding the more kin the more kids. 

So I put it together like this: social unrest leads to distrust of strangers leads to cousin marriages leads to ample fertility; tranquility leads to trust of strangers leads to marrying non-kin (and I explicitly mean anything past about 8th cousins) leads to insufficient numbers of kids leads to extinction.  The way to break the cycle, of course, is for people to know the facts.  That is why I invite you to look at them. 


M. Linton Herbert

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