In the bygone days of the pre-agricultural era, reproduction was, ahem, a simple matter of finding a healthy partner and a nice cave somewhere.

Then, right after mankind started farming, it suddenly became much more difficult for men to pass on their DNA. It was no longer enough to be strong and handy with an atlatl — fellows had to be rich and powerful too.

That’s according to a new study in the journal “Genome Research,” which analyzed more than 400 genetic sequences sourced from all over the world. Researchers found a “bottleneck” of male genetic material – when the diversity of Y chromosomes from men sharply declined.

Geneticists know of one other great “bottleneck,” or decrease in genetic diversity. That one happened about 50,000 years ago, as a small number of humans migrated out of Africa. That group would provide the gene pool for the subsequent populations of Europe, Asia and the Americas.

The difference with this later bottleneck is that it only involved male chromosomal material. The shift occurred between 4,000 and 8,000 years ago in nearly every community in the world, just after each community took up farming.

The correlation, researchers believe, is no coincidence: The advent of agriculture brought a concentration of power and resources in the hands of a few. Men with wealth and social standing became more desirable partners (and we know what Jane Austen said about what men in possession of fortunes want) and were better able to find reproductive success.

“Instead of ‘survival of the fittest’ in a biological sense, the accumulation of wealth and power may have increased the reproductive success of a limited number of ‘socially fit’ males and their sons,” Melissa Wilson Sayres, lead author and assistant professor at Arizona State University, said in a press release.

In a phone interview with The Washington Post, senior author Toomas Kivisild said that the mechanism of this not-so-natural selection process is still unclear. It may have been that rich and powerful men had more sexual partners (think Genghis Khan), or that the children of rich and powerful men were more likely to survive the harrowing ordeal of being a child during the Neolithic period.

While that may have been fine for the wealthier classes, a decline in genetic diversity may not be so great for the human race. “Having a high level of genetic diversity is beneficial to humans for several reasons,” said the press release. “… When the genes of individuals in a population vary greatly, the group has a greater chance of thriving and surviving – particularly against disease. It may also reduce the likelihood of passing along unfavorable genetic traits, which can weaken a species over time.”

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