October 7, 2008

Have Humans Stopped Evolving?

A leading British geneticist says that human evolution is coming to an end in the West due to a shortage of fathers over the age of 35, who are more likely to pass on genetic mutations to their children.

During a lecture today at University College London (UCL) entitled "Human evolution is over", Professor Steve Jones argued the case that there are three components to evolution "“ mutation, natural selection and random change -- and that the mutation rate is declining.  

"Quite unexpectedly, we have dropped the human mutation rate because of a change in reproductive patterns," Professor Jones said in an interview with The Times.

"Human social change often changes our genetic future," he said, adding that examples of such changes include marriage patterns and contraception.

While chemicals and radioactive pollution can alter genes, advanced age in men is one of the most significant mutation triggers, because cell divisions in men increase with age.

"Every time there is a cell division, there is a chance of a mistake, a mutation, an error," Jones 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."

"In the old days, you would find one powerful man having hundreds of children," Professor Jones added.  

He cites Morocco's fecund Moulay Ismail, who died in the 18th century, and is believed to have fathered 888 children by copulating with an average of 1.2 women per day over 60 years.

The lessening of natural selection is another factor at work as well.

"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 also plays a role.

"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. Worldwide, 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 global mass, and the future is brown."


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