Falling Sperm counts: 
A few years ago there was a flurry of interest in data that indicated that sperm counts of humans were falling all over the world.  It was actually worse than that.  Male gonads were getting smaller and were failing to develop normally more frequently.  I have not heard this tsk’ed over recently, but I suspect if it had proven false we should have heard.  The lack of interest is likely to be due to the lack of a cause.  A few causes were offered, pollution in the environment and estrogens in food among them. 

There is another theory.  It is based on something called Haldane’s Law.  This law holds that when two species are crossed so that the offspring become infertile, there is one sex that is predominately affected.  For instance in mammals, and insects for that matter, the female has two chromosomes labeled X while a male has an X and a Y.  If the two species are closely enough related to be able to have offspring at all, the males will become infertile even if the females don’t.  It is the opposite in birds, in which the sex chromosomes are labeled M and N.  The male has two that are alike, while the female has one copy of each.

It works in mammals.  Mules, hybrids of horse and donkey, appear to be females, even if they have the X and Y chromosome pattern.  When it comes to birds, I confess myself a little baffled. 

There is a kind of bird called the flycatcher, and it comes in two forms.  The pied flycatcher lives in Western Europe and Britain.  The male has little specks of white on a grey background while the female is brown.  In Eastern Europe and Asia one finds the collared flycatcher.  The male is grey with a little white band around its neck.  The two kinds of flycatcher have been known to be able to mate and produce offspring that are fertile, so they used to be thought of as a single species.

Then somebody did some counting of eggs and hatchlings and noticed something.  If a pied flycatcher mated with a pied or collared with collared then 90% of the eggs hatched.  If they crossbred, 90% of the eggs hatched.  But if a hybrid matted with anything, less than half of the eggs hatched.  So it seems that they are different species.  It was also found that the birds rather preferred to mate with like birds, and when one looked at the birds near the dividing line, the collared fly catchers had bigger collars and the male pied flycatchers looked rather like females.  So it all fit. 

My problem is that the difference was not the number of eggs but the number that hatched.  In other words, the females were doing their job making eggs, so it had to be the males that were not able to fertilize them.  That is not what I would have expected from Haldane’s Law.

But if it has been dignified with the name “Law,” we can take it seriously, my befuddlement aside. 

I have asserted, and I think it must be true, that ordinary hybrid infertility is just a continuation of the fall in fertility that occurs as the relatedness of a couple diminishes as seen in the Iceland study.  In that case, we could say that of course males are developing less well than we used to.  That is what we would expect as gene pool sizes increase to the point that infertility reaches crisis proportions. 

But it is not so simple.  It appears that at the same time the proportion of human pregnancies that go on to live childbirth is falling.  Maybe female humans are also not so excellently developed as in the past.  But it simply might be an increase in the proportions of pregnancies that have serious genetic problems.  Most genetic problems caused by too little relatedness probably simply produce zygotes, fertilized eggs, that never develop at all.  But some increase in the number that develop for a time before failing would not be a surprise. 

But there is another problem.  The Iceland study did not find that males were any different from females when it came to the relationship between relatedness and fertility.  So much for the application of Haldane. 

But in fact everybody in the study was an Icelander.  They are a very homogenous nation with very few, until recently, arriving or leaving.  It may simply be that the degree of unrelatedness sufficient to produce severe male infertility has not occurred.

One could look further into the matter.  If one had sperm counts on a large number of Icelanders, one could simply see if there was a correlation between low relatedness of the parents and low sperm counts.  It would also be interesting to know whether the falling birth rates that are a trouble to so many other rich countries also affect Iceland.  If not, one could undertake the difficult task of trying to duplicate the Iceland study in a place where the gene pool was bigger and more complex.  If that could be done, and the difficulties might prove insurmountable in terms of assembling a satisfactory genealogy and making some estimate of the genetic distance between parents that were very distantly related indeed, then we might indeed find the expected fall in male development in the presence of high degrees of unrelatedness.

Until the facts are in, that is one more reason not to feel hostile toward men who seem less manly than one expects.  It might he the doing of his parents. 

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