March 26, 2012

to be posted on and

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

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Dear Dr. Professor Harpending:

My interest is in the infertility that comes of not marrying kin and its impact on societies.  Yes, it’s real.  The short course is a single paper: An Association between Kinship and Fertility of Human Couples Agnar Helgason et al. SCIENCE vol. 329 no. 5864 February 8, 2008 page 813 – 816.  The longer version is here:
There is also a version I prepared for you earlier and emailed you as an attachment.  Since I did not mention it in the cover letter, I surmise you never looked at it and the letter itself made no sense at all. 

I was steered to your posting “Giving Bigotry a Chance” ( March 1, 2012 by my favorite blog I have read it and the correspondence that followed.  Among your interests is the genetic diversity of different populations.  And I have no objection to anything you said.  Oddly, my own interest is quite different.  From what I can tell, the dreaded infertility that comes of not marrying sufficiently close cousins (and in fact not too close cousins as it turns out) is not exactly genetic.  It appears to be mediated by epigenetic mechanisms.  Therefore it will in all likelihood not appear in your studies.  For instance Ashkenazi Jews seem all to be genetically kin to the degree of being the equivalent of fifth cousins.  Were fertility based on genes, then they should be doing right well.  Yet I understand they have a seriously depressed fertility rate just like everybody else in the developed world.

When I look at how this plays out in the question of “bigotry,” I find the result a bit surprising.  At least in the first generation, and probably even after multiple generations, ethnic grouping or other separation into large populations makes not difference.  You can marry across town or across the world, and if you are past, say, eighth cousin, it makes no difference at all to your fertility.  So those with an agenda to maintain genetic lines on that scale will get no fertility dividend.  But those with an agenda to achieve peace and cooperation by reversing the logic of maintaining genetic lines will pay a serious fertility penalty.  The problem with marrying across populations is not that the genetic difference is very great.  It is that it is generally out past eight cousin.  In the first generation the mechanism simply saturates, as you can tell by looking at the Orlando link above or just the Iceland paper. 

There is a discredited line of thinking called “eugenics.”  Their two main teachings were: don’t marry outside your “race” (whatever that means) and don’t marry cousins.  Well the first half is rejected, and its demise is applauded, as evidenced by at least one remark in the discussion of your posting.  And for my own purposes (and I understand not necessarily for yours) the first half is simply irrelevant.  On the other hand the second half is still a maxim that people clutch to themselves with passion.  One dear to me once told me a joke: “If two people get divorced in Kentucky, are they still legally cousins?”  Even I think it’s funny.  But neither the person telling the joke nor I would let hate jokes about race, religion, impairment, poverty, nationality, and so forth go unchallenged, nor would most others I think. 

So there is our defining prejudice.  And it is not just irrelevant; it is perverse.  The very people who most adamantly reject eugenics, are the ones most devoted to its second teaching.  In fact there was a meeting of the Genetic Society of America from which I was ejected for simply proposing that maybe we should take the matter of kinship and fertility seriously.  The grounds was that I was accused of promulgating eugenics.  Actually I was doing just the opposite.  It was the one who forbad me to attend who was serving the very eugenics he claimed to despise. 

The effects of helping closer kin rather than more distant kin (after all, we are all kin) seem to me rather small, but being genetic they should be quite durable.  The effect of marrying kin of an optimal distance is very strong indeed, although being epigenetic it is rather transient, only lasting a few generations.  But of course a few generations is enough time for this effect to wipe a population or a species out.  And extinction is very durable indeed. 


M. Linton Herbert MD 
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