November 3, 2009
25 St James’s Street
London SW1A 1HG
United Kingdom

Dear Sir:
In “Go forth and multiply a lot less” you do not mention that fertility is determined by kinship of a couple and their parents.  There is much evidence supporting this including a study from Iceland1 (reviewed by your in “Kissing Cousins” in your science section) sufficient but not necessary to prove the point.  Their published curves of fertility and reproductive success against kinship perfectly match yours of fertility against time and against GDP.  Obviously kinship is at the root of all.  Fertility in the developed world has been so low so long that for any child there are few if any potential future mates who are close enough kin for a marriage that could produce more than an only child.  At this rate there will soon be virtually none.  From then there can be no stabilizing much less recovery.   

In “The rich are different” you point out that there is still a desire in rich countries for babies and that progress has been made to increase fertility.  If the basic biology is ignored progress will never be sufficient.  The baby on your cover will be dashed against stones.  There simply must be public debate on this important science. 


M. Linton Herbert MD

1 An Association between Kinship And Fertility of Human couples Agnar Helgason, Snaedbjoern Palsson, Daniel F. Guobjartsson, Pordur Kristjansson and Karl Stefanson, SCIENCE vol 319 8 February 2008 page 813

I did not send them their own graphs back, but here are the two graphs I mentioned in the letter.  The first is the world fertility rate since 1950.

As you can see, it is the same curve we have seen before from the computer simulation, from the UN graph of birth rate against time for the three economically different regions of the word, from the Iceland study and from the Denmark study. 

And here is the same curve for the sixth time, this time fertility against national income.  Both graphs from “Go forth and multiply a lot less,” ECONOMIST, vol. 393 no. 8655 October 31, 2009 page 29/

They were also kind enough to send this link to their sources:

(Sorry I can't get the hyperlink to work today, but you can copy and paste it into your browser.)

Incidentally, in the posting entitled “Knuckle Walking” I mentioned that current thinking at that time suggested that chimpanzees developed knuckle walking and brachiating AFTER they and the human line had split; I did not think that made the slightest sense.  Well it has already been discredited.  The relevant reverence is “Fossil Primate Challenges Ida’s Place,” NATURE vol. 461 no. 7267 October 22, 2009 page 1040. 

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