How many new mutations? Natalie Savey/Millennium

WE’RE running just to stay still. A study of more than a million people going back four centuries shows that we are still evolving – not into superhumans, but to stay as we are.

Almost all children in rich countries now survive to adulthood. That has led some biologists to suggest that evolution has essentially stopped. The thinking is that if children are less likely to die, those with lots of adverse new mutations are more likely to pass these on, so natural selection is no longer stopping these genetic changes from building up in the population.

According to geneticist Michael Lynch of Indiana University in Bloomington, this process could affect our health and intelligence in just a few generations. Some have claimed that our genetic potential for intelligence is already eroding, and that IQ scores should have risen even more than they have over the past century due to better health and education.


But now there’s evidence that evolution is still removing our harmful mutations. Ruben Arslan of the University of Göttingen in Germany and his colleagues made this discovery by analysing church records from the 15th and 16th centuries from three areas – in Germany, Sweden and Quebec in Canada – and also in modern Swedish health records.

Studies have shown that for every extra year of their father’s life before they were conceived, a child has about two extra mutations. But Arslan’s team has found that the mutations of children born to older fathers are less likely to be passed on, because these children grow up to have fewer children themselves. Compared with a sibling born 10 years earlier, individuals born when the fathers were older had on average 5 per cent fewer children who survived beyond infancy (bioRxiv, doi.org/bdd3).

“Additional mutations are preventing the children of older fathers from reproducing as much”

The team thinks this is because the additional mutations are preventing the children of older fathers from reproducing as much as those born to younger dads. In this way, evolution still seems to be weeding out harmful mutations from human populations, stopping them from accumulating over generations.

But Lynch points out that even though there may be some evolution taking place, this selection may be weaker than it used to be. This means that over longer periods of time, mutations could still build up in human populations, albeit more slowly.

Even so, Arslan’s work suggests that we can worry less about recent trends towards having children later in life. Although the age at which men first become fathers has crept upwards in the past half-century, the average age of each child’s father is still lower now than it was in the 16th century, the study found.

This is because people used to have more children, starting their families earlier, but continuing to reproduce until late in life. In Sweden, between 1737 and 1880, the average age of a baby’s father at their time of birth was 35, a couple of years older than dads in Sweden today.

This article appeared in print under the headline “Old-dad evolution is protecting our health”