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.

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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.”

Professor Jones added: “In the old days, you would find one powerful man having hundreds of children.” He cites the fecund Moulay Ismail of Morocco, who died in the 18th century, and is reputed to have fathered 888 children. To achieve this feat, Ismail is thought to have copulated with an average of about 1.2 women a day over 60 years.

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.”

Decreasing randomness is another contributing factor. “Humans are 10,000 times more common than we should be, according to the rules of the animal kingdom, and we have agriculture to thank for that. Without farming, the world population would probably have reached half a million by now – about the size of the population of Glasgow.

“Small populations which are isolated can evolve at random as genes are accidentally lost. World-wide, all populations are becoming connected and the opportunity for random change is dwindling. History is made in bed, but nowadays the beds are getting closer together. We are mixing into a glo-bal mass, and the future is brown.”

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