Wars and clan structure may explain a strange biological event 7,000 years ago

Starting about 7,000 years ago, something weird seems to have happened to men: Over the next two millennia, recent studies suggest, their genetic diversity specifically, the diversity of their Y chromosomes collapsed. So extreme was that collapse that it was as if there was only one man left to mate for every 17 women.Anthropologists and biologists were perplexed, but Stanford researchers now believe they've found a simple if revealing explanation. The collapse, they argue, was the result of generations of war between patrilineal clans, whose membership is determined by male ancestors.