June 29, 2011
open letter to be posted on nobabies.net

Professor Niels E. Skakkebaek
Rigshospitalet, Department of Growth and Reproduction
Blegdamsvej 9
2100 København Ø
Fax number 35456054

Dear Professor:
When I read the article that mentions your data (Danish sperm counts spark data dispute Gretchen Vogel SCIENCE vol. 332 no. 6035 June 17, 2011 page 1369) my initial reaction was to rejoice.  On the face of it, Danish sperm counts of army recruits seem to have stabilized.  On reading further, I see that you are involved, know about the stability and are still worried because the sperm counts may be stable but are at a low level.  Bear with me; I hope I have something to offer.

First comes what may be a surprise.  Normal fertility requires a substantial degree of consanguinity.  I am enclosing a letter I recently wrote to Leonard Susskind explaining that the fact of evolution requires this to be true and giving a thumbnail sketch of the evidence that it is indeed true.  Alas, in my letter to him when I list some of the strategies that may have evolved to enforce consanguinity – or rather to exterminate any population that fails to maintain sufficient consanguinity – I failed to mention the possibility that nature might tamper with our minds and instill in us an aversion to consanguinity so forcing us into oblivion before we can do more harm.  Otherwise the letter was pitched for a man who had won a Nobel Prize and with whom I felt no need to pull intellectual punches.  The same goes for you.  Since that letter, like this, is to be made public, you are by no means intruding on him by reading it.  (Sorry to use snail mail, but my email to you came back.)

If we then might take as read that consanguinity is necessary for fertility, the next question is whether the mechanism is prezygotic or postzygotic.  The Helgason article I refer to in his letter shows that failure of consanguinity reduces both the number of children and the number of grandchildren so most likely there are both at least one prezygotic mechanism and at least one postzygotic mechanism such as reduced sperm count. 

If you are interested in sperm counts, then, it would seem to be reasonable to compare sperm counts with the consanguinity of the parents of the recruits that were tested.  This would seem at first not to be convenient.  But work has been done right there in Denmark that might be helpful.  Rodrigo Labouriau did a study in which he compared “marital radius” or distance between birthplaces of a couple and “urbanization” or how big a town they lived in and found that fertility decreased with urbanization – as you would expect since that means less consanguinity – but increased with marital radius – which seemed paradoxical.  But that was only true out to 100 km.  I wrote and encouraged him to look farther out in distance and farther back in time.  He did and demonstrated in an article in the journal Science that now fertility did fall off with consanguinity.  Both those references are in the Susskind letter.

Since Helgason was looking at consanguinity – which is inversely proportional to population size – and Labouriau was looking at distance – which is inversely proportional to the square root of population size, their graphs looked different.  Correct the geometry, though, and they complement each other nicely.  I had high hopes that the two would team up and get to the bottom of matters, but alas they did not seem to be in a mood to cooperate. 

While Helgason has consistently refused to answer any letter of mine, Labouraiu was courteous enough to answer me more than once.  I think it might be possible to work with him.  His contact information is:

Rodrigo Labouriau
Department of Genetics and Biotechnology
Faculty of Agricultural Sciences
University of Aarhus
Blichers Alle
Postbox 50

A pressing question is this: if you compare your sperm count data and his marital radius data do you get a correlation?  You might not.  The sperm count mechanism may have saturated. 

At least one mechanism does indeed saturate.  If you go to gapminder.com and have the program graph total fertility (It’s the first choice they give you) on the horizontal axis and age of first marriage of women (It’s under the “population” button) and run the data through the decades you will find that in country after country fertility falls to below replacement and then stabilizes while age at marriage abruptly starts upward.  It appears that one mechanism has saturated while another is taking over.  Obviously you cannot keep fertility constant while age at marriage rises forever. 

But there is another possibility.  Perhaps over the years the army recruits have come from smaller towns and more consanguineous couples.  This would account for sperm counts that appeared stable when they in fact were not.  So it is a control that very much needs to be done. 

Let me know what you think.  If I can be of any assistance of course I am at your disposal.


M. Linton Herbert MD 

There have been 17,262 visitors so far.

Home page