10/06/2008

The Key to human evolution: Men older than 50 having children?

The Times of London has this take on why mankind will slow its evolution:

Human evolution is grinding to a halt because of a shortage of older fathers in the West, according to a leading genetics expert.

Fathers over the age of 35 are more likely to pass on mutations, according to Professor Steve Jones, of University College London.

Speaking today at a UCL lecture entitled “Human evolution is over” Professor Jones will argue that there were three components to evolution – natural selection, mutation and random change. “Quite unexpectedly, we have dropped the human mutation rate because of a change in reproductive patterns,” Professor Jones told The Times.

“Human social change often changes our genetic future,” he said, citing marriage patterns and contraception as examples. Although chemicals and radioactive pollution could alter genetics, one of the most important mutation triggers is advanced age in men.

This is because cell divisions in males increase with age. “Every time there is a cell division, there is a chance of a mistake, a mutation, an error,” he said. “For a 29-year old father [the mean age of reproduction in the West] there are around 300 divisions between the sperm that made him and the one he passes on – each one with an opportunity to make mistakes.

“For a 50-year-old father, the figure is well over a thousand. A drop in the number of older fathers will thus have a major effect on the rate of mutation.” . . .

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3 Comments:

Anonymous Munango-Keewati said...

He's overlooking two things:

1) Most men didn't live to the age of fifty until recently.

2) Populations were much smaller in the past.

Massively larger populations plus a much greater male longevity is more likely to equal more mutations (mostly deleterious).

--M-K

10/06/2008 11:35 PM  
Blogger John Lott said...

The longevity issue is some what misleading. It is true that life expectancy at birth has doubled in just the last 100 years, but most of that change is from eliminating deaths at birth or at a very young age.

The total population point is interesting. It is not clear what this says about whether any mutations will make it into the overall gene pool. As the piece notes, there is not the same weeding out of weaker characteristics that we used to have.

10/07/2008 12:16 AM  
Blogger author said...

Actually, I would believe a larger population would restrict mutations from accumulating in the population even though the frequency of mutations increase. This is because most mutations are deleterious and will be selected against, especially when there are other alleles in the population that have a higher fitness.

In small populations, genetic drift takes over. Genetic drift is just a type of sampling error. Instead of a mutation being passed on to the next generation due to fitness, the mutation is put in the next generation purely by chance.

If you want more information about mutations, look at the microbial evolution experiments in which the researcher creates mutation accumulation lines.

I also have a problem with this article in that I have seen no evidence that there is a decrease in the age of men having children in the West. In face, I would think that the age of men having their first child has increased as I see more people waiting to have children later in life.

10/07/2008 12:23 AM  

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