The small band of Homo sapiens that left Africa around 60,000 years ago, taking the first steps on a journey that would eventually disperse humans all around the world, may have been composed mostly of men.
A new analysis of DNA variations in contemporary humans indicates that non-Africans descend from a population that contained far more males than females [New Scientist].
In the study, published in Nature Genetics [subscription required], researchers compared genetic samples from present-day African, European, and Asian populations. They were looking at the chromosomes that determine sex (two X chromosomes in women, one X and one Y chromosome in men), as well as the other 22 chromosome pairs, which are the same in both sexes. They examined
the rate at which mutations randomly spread through the X chromosome over dozens or hundreds of generations as compared to the mutation rate in other, non-sex, chromosomes [AFP].
When researchers compared African and non-African populations, they found that the X chromosome accumulated mutations faster than other chromosomes after these populations split, which indicates that non-Africans derived from a small female gene pool. However, when they compared European and Asian populations they found that the X chromosome and the non-sex chromosomes accumulated changes at about the same rate.
“These results point to a period of accelerated drift on chromosome X that largely occurred after the split of West Africans and non-Africans, but before the separation of North Europeans and East Asians,” [GenomeWeb News]
, the researchers wrote. The researchers say the most likely explanation for these discrepancies is a long-distance, primarily male migration out of Africa around 60,000 years ago. Study coauthor
Alon Keinan said the findings are "in line with what anthropologists have taught us about hunter-gatherer populations, in which short-distance migration is primarily by women and long-distance migration primarily by men" [UPI].
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