A large-scale genetic study links ancient male population bursts to migration, conquests, and technology
Human chromosomes stand in pairs, swapping DNA to produce new gene combinations. But the Y chromosome stands alone, unable to trade genes with its X counterpart.
What this means is that the Y chromosome gets passed largely intact between father and son. Only through random mutations do the Y chromosomes of a man’s descendants slowly diverge from each other over generations.
In a collaborative study involving 42 scientists on 4 continents, researchers compared the Y chromosome sequences of more than 1200 men from 26 populations around the world using data generated by the 1000 Genomes Project.
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David Poznik, first author on the paper that was just published in Nature Genetics, said: "We identified more than 60,000 positions where one DNA letter was replaced by another in a man with modern descendants, and we discovered thousands of more complex DNA variants. These data constitute a rich and publicly available resource for further genealogical, historical and forensic studies."
The scientists used the rich genetic information to build a detailed family tree, which confirmed the existence of a common male ancestor living approximately 190,000 years ago.
Even more intriguing was the finding that the tree had a bush-like branching pattern in certain places.
Yali Xue, lead author from the Wellcome Trust Sanger Institute, explained, "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."
The earliest identified male population burst occurred 50,000-55,000 years ago — this period corresponds closely with population increases that have been established through the archaeological record, such as the first expansion of humans across Europe and Asia. Plenty of resources would have been available to support increasing populations on these vast, unoccupied continents.
Evidence of a second population burst around 4,000-8,000 years ago was harder for the scientists to explain.
Dr. Chris Tyler-Smith, from the Sanger Institute, offers some ideas. This was a period of great technological advancements, such as wheeled transport and metalworking, and also a period marked by organized warfare and conquests — all of which might have fueled an explosion in male numbers. He notes that these candidate explanations require further investigation.
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