Joshua G. Goldstein
Max Planck Institute for Demographic Research
Konrad-Zuse-Straße 1
18057 Rostock

Dear Joshua Goldstein:
With a mixture of great surprise and astonishment I have read with attention the ten year prediction “Demographics” NATURE vol. 463 no. 7277 January 7, 2009 page 30.  The foreshadowed ageing of Europe is beyond question.  What is missing is a consideration of the birth rate.  Although I lack your resources, I do infer something of great importance.  Reasoning from the age distribution of German children under 10 years old, which seems to show a linear decline toward younger children, the last German girl who will grow up to have a baby is now about 10.  Unless something remarkable happens, from that time the zero birth rate will sweep across the age spectrum like a windshield wiper.  All in all the same prediction probably holds for the rest of the developed world, although countries other than Germany confound easy analysis by including the offspring of immigrants.  (The effect accumulates over generations, so immigrants can have a high birth rate for a generation or two.)  

The sad thing is that this fall in birth has now been explained.  Cities have never been able to produce enough babies to survive without recruitment.  I could almost say give me a century and I can tell you what the then current misconception as to the cause was.  The current one is the Free Choice argument.  But the relationship between average kinship of couples and their fertility follows the same pattern in humans (2 excellent studies in a refereed journal) and in over 1,000 animal studies.  I do not believe rabbits postpone having their families for career reasons. 

The less developed world is not far behind.  In ten years the Mexican birth rate will fall below replacement and I suspect the same holds for the other less-but-not-least developed world.  There are references on the enclosed DVD and of course I am available to help in any way I can if you have any question or difficulty following up the leads.  There is more at 

You cheerfully note that Sweden is not very far below replacement.  When I studied there at Lund many years ago, the student body was organized into “nations” for social purposes.  The nations represented the different provinces so there was at least some gesture toward keeping a local identity.  It was not enough, but it seems to have helped.  Then, ever optimistic, you announce that a small rate of immigration will stabilize Sweden’s population. 

That would be nice.  However I am reminded of this painting by Salvador Dali: Soft Construction with Beans at the Philadelphia Museum of art.  (We have a large Dali collection here in Pinellas County.) 
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I do not mean that different ethnic groups cannot play nicely together.  What I mean is that as you expand the gene pool people are ever more likely to marry and try to have children outside of a biologically safe circle.

Think of those as mismatched genes trying to get together to make a child.  Sometimes they just can’t get it to work.  (Sorry about the poor reproduction, but you can follow the link on the internet, and some day I shall get around to posting it on my website.)

Given that aging population is going to be the issue of the century, and given that the cause is now evident, I am hoping you will take an interest.  From a demographic standpoint there are a number of things that could be done.  For one thing, the linear decline visible in the least 10 years in Germany and Mexico should be evident in many places.  For another, it should be possible to look at same-aged cohorts of Germans over their reproductive spans and see what the shape of the fertility-against-age curves have been.  I suspect that the curves will be parallel (at least during times of relative stability) adding more evidence to the concept that fertility is inherent, not dictated by outside social issue. 

Please let me know what you think.


M. Linton Herbert MD and Silent 

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