May 19, 2011

Fred Pearce
Author of The Coming Population Crash

Dear Fred Pearce:
I wrote you about a year ago and you were one of the very few kind enough to respond.  I make bold to write again on the occasion of your amazing article Dubious Assumptions Prime Population Bomb NATURE vol. 473 no. 7346 May 12, 2011 page 125.  You point out that the UN now predicts a higher population in 2100 than it predicted previously, that this upward revision is not the result of new data but a result of assuming that fertility would stabilize at 2.1 children per woman rather than the previously assumed 1.85 children per woman, and that there is no apparent justification for the change. 

Forgive me for pulling out some numbers I found about birth rates as measured by the UN.

(If these graphs don’t come through the internet, let me know and I’ll snail them to you.)

You have to wonder whether they look at their own numbers.  1.85 children per woman as the leveling off point doesn’t look so bad.  It looks to me like the world is following a demographic trajectory that is the same everywhere.  We are just at different points along the curve.  As you might recall from my previous letter, I cannot image this is due to free will.  And in fact the phenomenon has been documented in humans and animals in the literature. 
R. Sibly et al., Science 309, 607 (2005). 
A. Helgason et al., Science 319 813 (2008).
R. Labouriau, A. Amorim Genetics 178 601 (2008).
R. Labouriau, A. Amorim Science 322 1634 (2008).

As you also might recall, if you have superhuman mnemonic powers, I don’t see this playing out well in the end.  Certainly in vitro fertilization seems to be buying some slack for the developed world, but if you go to and graph fertility on one axis and age at first marriage for women on the other axis and follow them through time, you will see that the decline in fertility levels off indeed, but simultaneously women start getting married later and later.  Than cannot remain stable for very long.

But the real point for me now is the issue you raise.  Why in the world did the UN make such a hash of the statistics?  The low birth rate in other times would have caused stark panic in other times.  Yet when I raise the question, “Where does fertility stop falling?”  I get the answer, “It’s just what people choose,” even though the articles make clear that this is not the case.

So the unaccountable UN change is part of a far bigger phenomenon.  People just want to believe that there are too many children.  You would think that evolution would have put children higher on our list of emotional priorities.  As so it was, at one time.

I find myself edging into the murky notion that nature is contriving our demise.  I hate to go there.  But there is another pattern.  There is the prejudice against having cousins.  Charles Darwin said it was a bad idea – caused insanity and so forth.  His son took a careful look at the numbers and found that in fact to a small degree it protected against insanity.  I’m pretty sure that was because it reduced the incidence of Rh incompatibility.  Proper genetic screening would have removed that effect.  Of course proper genetic screening would remove almost all the negative genetic results of marrying cousins.  Yet the prejudice remains. 

And that is not a trivial matter.  As the references make clear, you must marry sufficiently close cousins or your population will die out.

If you wish to see my reasoning as to why nature should do such a dastardly thing to us, go to my web site and look at the Vancouver poster I put up this past March 18.  There are regrettable computation errors in it, but the reasoning of the first part I believe to be hermetically tight. 

Thanks for the fine article and the best of luck in your continuing efforts to bring rationality to this important issue.


M. Linton Herbert MD

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