by Silvia Turin
Men have historically fathered children who are, on average, about seven years older than women. Analysis of genetic mutations would allow us to trace the ages of the parents back to 250,000 years ago
Fathers have predated mothers since the beginning of time, or rather since our species came into existence over 250,000 years ago. This is suggested by research by Richard Wang’s team, an evolutionary geneticist at the University of Indiana at Bloomington (USA), published in Science Advances. Previous estimates were limited to around 40,000 years ago.
Analysis of mutations
In the absence of documents, how did he and his colleagues determine the age of the parents from generation to generation? By detecting spontaneous mutations in modern human DNA. All children have new mutations that their parents don’t have, a phenomenon we know from viruses and genetic variants. These mutations arise when DNA is damaged before conception, or occur due to random errors during cell division. Research suggests that older parents pass on more mutations than younger parents.
The development of a software
So Wang and his colleagues first conducted the study on a group of Icelanders (who have been sequencing the genomes of all islanders for 25 years): using software, they analyzed data from a 2017 study that included about 1,500 Icelanders and their parents who had monitored the age of conception and the genetic changes that occurred in 3 generations. The program learned to associate certain mutations and their frequency with the age and gender of the parents.
After developing the computational tool, the scientists applied it to the genomes of 2,500 modern humans (from around the world) to identify mutations that occurred at different times in human history. By dating when these mutations appeared, the team was able to map the average ages of mothers and fathers over thousands of years.
The end results
The researchers found that 26.9 years was the general median age of conception over the past 250,000 years. However, a gender breakdown showed that men were on average around 30.7 years old when they conceived their first child, compared to 23.2 years for women. The numbers varied over time, but the model suggested that men consistently had children later in life than women.
The older age of fathers can be explained biologically: men can have children later than women, but social factors could also play a role, for example the pressure on men in patriarchal societies to establish status earlier in order to become fathers.
The critic
Critics of the study say the computer model does not adequately account for other factors (including environmental exposure) that may have played a role in causing the mutations. More populations need to be sampled to reliably reconstruct the age of conception over thousands of years, but this study, the authors argue, provides “reasonable estimates” that can help researchers gain insight into the lives of early humans.
Jan 23, 2023 (change Jan 23, 2023 | 11:28 am)
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