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How a few Bronze Age forefathers gave rise to most of Europe's men

New research suggests that the demographic expansion of Europe, beginning about 3,300 years ago, involved fewer men than women.

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If you think the dating scene is hard today, try Bronze Age Europe.

New genetic research suggests that widespread population growth occurred in Europe 3,300 years ago – far more recently than previously thought. And according to a study published Tuesday in Nature Communications, only a small number of men contributed to that growth.

As part of an international research collaboration, University of Leicester researcher Chiara Batini extracted DNA from the saliva and blood of 334 male participants. The men were all unrelated, and came from 17 different populations in Europe and the Middle East. Utilizing a process called next-generation sequencing, Dr. Batini and colleagues were able to organize large segments of DNA to highlight variations between the samples.

From there, researchers narrowed in on the sex-determining Y chromosome. The presence of the Y chromosome means a person is genetically male; by sequencing over 3.7 million base-pairs, researchers were able to reconstruct patrilineal (father to son) genealogies.

The origins of Europeans – and the extent to which “modern” European ancestries can be traced back to the Paleolithic and Neolithic eras – is widely debated. Batini and her colleagues found that 13 of the 17 populations studied underwent “very similar” expansions at roughly the same time, about 3,300 years ago.

“The [previous estimate] was that the Y chromosomes observed today were brought into Europe during the diffusion of agriculture between 10 and five thousand years ago,” Batini says. “Here, however, we observe a ubiquitous demographic expansion across Europe dating back only to the Bronze Age, thus much more recent than previously thought.”

But as populations grew in Bronze Age Europe, genetic diversity declined. In Batini’s genealogies, only some Y chromosomes were passed on. In other words, a shrinking pool of men were reproducing with a stable number of women.

“Yes, most European populations grew in number since 3,300 years ago,” Batini says, “but what we see is that only some Y chromosomes, or men, were involved in these expansions. This does not mean there were fewer men than women in terms of numbers, but that fewer men than women contributed to the following generation [by reproducing]. This might be due to social factors, such as power, resources, and wealth being more easily accessible to only some men at around 3,300 years ago.”

In a separate study published by Genome Research, scientists found a bottleneck in the genetic diversity of male lineages across five continents. That decline occurred somewhere between four and eight thousand years ago. Researchers from Arizona State University and the University of Cambridge attributed the shift to cultural changes – wealth and power became more important than biological fitness in matters of reproduction. As a result, roughly 17 women reproduced for every one man.

In some ways, these findings aren’t so surprising. Agricultural societies center around land and property. The more land and property you have, the more wealthy and powerful you can become. Batini and her colleagues are slowly unraveling a complex and intertwining genetic history in Europe, but their work also touches on loftier human concepts, namely, social stratification and human attraction to power.

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