A new study in human genetic history reveals that the species had several male population explosions across five continents between four and 55 thousand years ago.
Thanks to the unique characteristics passed down from father to son on the Y chromosome, researchers were able to trace the genetic histories of more than 1200 currently living men from 26 different population groups around the world and found patterns going back in time that revealed not only how all 1200 are related to each other (thought to be descended from a single man who lived approximately 190,000 years ago) but how at various times over human history there were major increases in male populations within a short span of time, the earliest occurring across Asia and Europe sometime between 50,000 and 55,000 years ago and then again across the Americas about 15,000 years ago.
“This pattern tells us that there was an explosive increase in the number of men carrying a certain type of Y chromosome, within just a few generations. We only observed this phenomenon in males, and only in a few groups of men,” says Dr. Yali Xue of the Wellcome Trust Sanger Institute and lead author of the study, published this month in the journal Nature Genetics.
Researchers based their findings on data generated by the 1000 Genomes Project, an international collaborative undertaking that ran between 2008 and 2015 which sequenced the genetic makeup of over 1000 individuals from diverse ethnic backgrounds. The project aimed at providing the most detailed and comprehensive catalogue of human genetic variation and, once completed, made the data freely available to the general scientific community.
As to the cause of these population booms, researchers speculate that the more ancient expansions were the result of the first waves of migration into new and previously uninhabited territories where an abundance of untapped and competition-free resources engendered prosperity and rapid population growth.
The more recent expansions are more difficult to justify but researchers suggest that technological developments could be at root. “The best explanation is that they may have resulted from advances in technology that could be controlled by small groups of men,” says co-author Dr. Chris Tyler-Smith of the Sanger Institute. “Wheeled transport, metal working and organised warfare are all candidate explanations that can now be investigated further.”
Despite these brief explosions, however -and despite the fact that today the number of men on the planet outnumbers that of women (but not in many developed countries, including Canada) -geneticists maintain that, historically, the female of the species has been the more populous sex.
In a 2014 study researchers compared historic genetic variations of both paternally-inherited Y chromosome (NRY) and maternally-inherited mitochondrial DNA (mtDNA) and found higher levels of maternal genetic diversity at key points in human history, indicating that there were more females than males present. The researchers estimated that when the first humans left Africa for the Cradle of Civilization (modern-day Iraq and Kuwait) some 75,000 years ago, there were likely fewer than 100 migrants with a group makeup of just 15 men and 26 women.