October 15, 2015

Brother Guy Consolmagno AMGD
Vatican Observatory
Vatican City

Dear Brother Guy:
I was breezing past your interview (Edwin Cartlidge, Talking Science and God with the Pope’s New Astronomer Science vol. 350 no. 6756 October 9, 2015 page 17) when I was arrested by your first answer.  After studying astronomy you felt it was more important to see to people’s needs, like having enough to eat, but on arriving in Africa with the Peace Corps to attend them, you found people thrilled with the idea of learning astronomy. 

My experience has been rather contrary to that.  It turns out that in order to survive more than – I’d guess – three or four generations a population has to have a substantial portion who marry cousins.  It’s true of animals, as well.  Tracking down the reason for this, as well as evidence that it is visible in history, has been for me fascinating.  This year Professor Robin Fox wrote chapter 19 “Marry in or Die Out” in the textbook Handb00k on Evolution and Society, so it is not a wild speculation.  This is bedrock, well established science – just little known. 

From the evidence I have found, first cousins are too close to have the highest quality of children.  Third cousins maximize grandchildren.  Don’t go out to ninth cousin or beyond; that way extinction lies.  (Of course this has nothing to do with ethnicity; tenth cousin is indistinguishable from the far side of the world.)  Now I have heard, and alas kept no record of same, that there was a time when the Catholic Church discouraged marrying closer than sixth cousins.  This strategy is not without merit.  It is just about at that level where a couple can expect to have roughly the 2.1 children and 4.2 grandchildren that are needed for a stable population.  Both growth and decline, of course, are problematic in the long run.  I suspect that decline is more dangerous.  If you look at birth rates of rich countries on, you will see that they have fallen and then stabilized just below replacement.  However age of marriage at that point begins an inexorable rise.  Obviously that is not a stable situation. 

The science strikes me as interesting, but what puzzles me is that nobody seems to care.  We’re talking babies and family, here.  What could be more important and exciting?  I would think that the social media would light up everywhere, but there is silence.

I don’t mean to unload a lot of grief on you.  I just want to emphasize your observation.  The sky fills the soul with wonder.  The brutal mechanics of how we can have enough babies seems to go the other way. 

If you want to know more, of course, I’d be happy to send you links to most of it.  If you can’t find that textbook, maybe I can help.

All best wishes,

M. Linton Herbert

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