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For a man’s Y chromosome to gain immortality, he needs not only fertility but also power, ensuring he has many sons who survive and thrive. Genghis Khan, founder and emperor of the Mongol Empire in the 1200s, is one example: about 0.5% of the modern world’s Y chromosomes come from him.
Now, new research on Y chromosomes in Asia has found 10 more genetic clusters from highly productive males throughout history. The most recent clusters originated in pastoral nomadic societies, the kind that generated long-lived and far-ranging dynasties.
“It’s interesting that social selection can lead to changes in genetics,” said co-author Mark Jobling at the University of Leicester, UK. “Understanding the interaction between natural selection and social selection and sexual selection is a really interesting project.”
To do the analysis, Evelyne Heyer’s group at the Sorbonne in Paris traveled throughout Central Asia, gathering 461 DNA samples from groups all over the continent; in addition, the team used 4860 DNA samples that were part of previously-published datasets, totaling 5321 males from 127 different populations.
“We combined two marker systems—the slow changing SNP with the fast-changing STRs—to give us a picture of the variation both on a deep timescale and on a shallow time scale,” said Jobling.
The researchers identified 15 unusually frequent haplotypes (present more than 20 times in the 5321 men) on the Y chromosome. They then used a novel algorithm to find 11 descent clusters (DCs), which are haplotypes stuck with certain common mutations that all come from the same original male. Then, “based on the amount of diversity that’s accumulated, we can estimate how long ago that was,” said Jobling.
The team found that six DCs originated in protohistorical times, while four began in historical times (one DC was dropped earlier in the project). The older, pre-Bronze-Age DCs often came from agricultural societies, while the more recent DCs were mostly pastoral nomads, usually ruled by dynasties (including the Genghis Khan cluster). The increasing use of horses in these societies encouraged trade as well as war, as mobile pastoralists were able to more easily conquer sedentary groups. Dynasties ruled for generations, allowing the Y chromosome of powerful rulers and their sons to flourish and survive for thousands of years.
Studies like these can lead to better forensic analysis of Y chromosomes, which are assumed to be different between people but, as this study shows, may be quite similar in some populations. They also help us understand human evolution.
“This isn’t natural selection. It wasn’t that the Y chromosome of the founder was somehow better at making faster sperm or something like that,” said Jobling. “What we see here is the effect of culture on genetics.”
Balaresque P, Poulet N, Cussat-Blanc S, Gerard P, Quintana-Murci L, Heyer E, Jobling MA. Y-chromosome descent clusters and male differential reproductive success: young lineage expansions dominate Asian pastoral nomadic populations. Eur J Hum Genet. 2015 Jan 14.
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