Mutating old men again:
They’re back. (Ewen Callaway Fathers Bequeath more Mutations as They Age, NATURE vol. 488. no. 7412 August 23, 2012 page 439) The interest in old men and their mutations continues. It has long been known that children of men who grow to be old do better than the children of men who die younger. It has also been known for a long time that other things being equal the children of younger men do better than the children of older men.
Well they’ve gone and got the evidence that one factor may be mutations. There are apparently about 6 new mutations per person per generations. (Alexey Kondrashov The Rate of Human Mutation, page 467 in the same issue) and about one in ten of these mutations is actually harmful one way or the other. And a 36 year old will pass along about twice as many mutations as a 20 year old while a 70 year old will pass along eight times as many.
I had earlier made the mental reservation that an older man might indeed pass along more new mutations but since he is from an earlier generation there has been less accumulation of them. That now appears not to hold water. Of course the other side of the coin remains that the seventy year old is a proven product. If he is still interested in having children, he may not be as good a bet as he was at 20, but a lot of those 20 year olds are going to have problems turn up that prevent them from reaching a fertile 70.
There is a piece of apparently good news. They say that having older men does not presage a population collapse. Icelandic men in the seventeenth and eighteenth century fathered children when the men were average age 34 to 36. So the age can go back down.
I am not so sure I accept that comfort. Watching on gapminder.com how age at first marriage rises once fertility falls below replacement shows no case of the age at which women first marry turn back. It just keeps going up. That would suggest, that there was indeed a meltdown in Iceland. A more privileged segment of the population was lost and a less privileged segment with adequate birth rate and viable age of first marriage replaced them. Indeed, they say that although Iceland was essentially completely settled by Vikings, if you look at the population now they are genetically closer to Scotland than to Scandinavia. That would go along with a handful of what had been Scottish slaves not gaining true equality until their old masters had died out.
This would be a matter of fact. Either it happened or it did not. And the exhaustive Icelandic genealogy would prove it one way or the other. Therefore there is little point in piling on argument. If anybody thinks it’s important, they need to get next the data.
At all events, I’m sticking to my guns on one point. There is no advantage in not getting born. Even if old men do carry more undesirable genes, they still represent one way of reaching back in time for a generation or so when fertility was higher. As the article suggests, maybe having a man’s sperm frozen when he is twenty to be thawed and used later seems to be pretty valid, assuming of course that there is no genetic nor epigenetic change induced by the storage and recovery process.
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