About 7,000 years ago, something weird happened to men: the genetic diversity of their Y chromosomes collapsed. It was as if there was only one man left to mate for every 17 women. The collapse may have been the result of generations of war between patrilineal clans structured around male ancestry.

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About 7,000 years ago, something weird happened to men: the genetic diversity of their Y chromosomes collapsed. It was as if there was only one man left to mate for every 17 women. The collapse may have been the result of generations of war between patrilineal clans structured around male ancestry.