I’ve read Steve Jones’ books and enjoyed them — so I’m really baffled by this bizarre report of a talk he gave. It’s either a massive example of misreporting, or Jones has a solid grip on everyone’s ankles and he’s straining to pull our legs right off.
He claims human evolution is over. The reason? Because not enough fathers over 35 are having children. That’s bad because mutations are the source of evolutionary novelty, and older fathers are more likely to have accumulated errors in the replication of sperm, and therefore pass on more mutations.
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.”
This is true, but it makes no sense. It’s not as if younger fathers produce no mutations — they generate plenty. It’s a difference in degree, nothing more, so we still have plenty of new mutations percolating into the population. And of course, over most of human history parents have been relatively young, since you couldn’t count on living to the age of 35.
And then there’s this odd argument.
Another factor is the weakening of natural selection. “In ancient times half our children would have died by the age of 20. Now, in the Western world, 98 per cent of them are surviving to 21.”
That makes even less sense. Natural selection is going to eliminate variants; by reducing its effects, we permit more mutations to persist in the population. One moment he’s complaining that fewer mutations are being produced, the next he’s complaining that the mutants are thriving. Which is it?
I’m thinking Jones must be making some colossal joke here, or maybe he’s testing his audience to see how much illogic and absurdity they will accept. That’s the only way I can explain these strange claims.
I see that Larry Moran has just thrown up his hands in exasperation at all the errors.