At what age did our ancestors become parents in the past 250,000 years? The question might seem beyond the reach of scientific analysis. However, American geneticists have taken up the challenge and published their results in the journal Science Advances of January 6. Knowing the average period that separated two successive generations (parental age) is important. “This generational time makes it possible to date the genetic changes of our species, it is the carbon 14 of archaeologists”notes Etienne Patin, CNRS researcher at the Institut Pasteur, in Paris.
This is how geneticists usually proceed. They compare the genome of various current populations to find mutations – letters of DNA that differ between individuals. With each generation, these mutations accumulate: they are found in modern humans, whose genome is a manuscript of the history of our species.
By deciphering this manuscript, researchers are able to calculate the age at which each mutation appeared in the DNA of our ancestors. How ? By examining the DNA sequences surrounding it. « The more recombination events observed [des échanges de fragments d’ADN] around a given mutation, the older it ise », explains Lluis Quintana-Murci, professor at the Collège de France and the Institut Pasteur. But the age of a mutation is expressed in “number of generations”, which must be converted into years. How ? By multiplying it by the famous generational time.
Population geneticists have thus estimated that the last exit from West Africa A wise man populating the rest of the world dates back 2,700 generations. By multiplying this number by 28, the hitherto estimated average value of the generational time of our ancestors, they dated this exit from Africa at 75,000 years.
The age gap between father and mother has narrowed
This estimate, however, was based on measurements made in contemporary hunter-gatherer societies and in the post-industrial society of the last two centuries. « We were left in the dark », says Etienne Patin. What does the new study show in Science Advances ? Over the past 250,000 years, the average parental age has been 26.9 years for both genders. So far, no surprises. The following is more unexpected: “The variability in generation time comes mainly from men. The average generation time of women has remained relatively stable »specifies the coordinator of the study, Richard Wang, of the university of Indiana (United States).
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