Michelle Starr in Science Alert:
Around 7,000 years ago – all the way back in the Neolithic – something really peculiar happened to human genetic diversity. Over the next 2,000 years, and seen across Africa, Europe and Asia, the genetic diversity of the Y chromosome collapsed, becoming as though there was only one man for every 17 women.
Now, through computer modelling, researchers believe they have found the cause of this mysterious phenomenon: fighting between patrilineal clans.
Drops in genetic diversity among humans are not unheard of, inferred based on genetic patterns in modern humans. But these usually affect entire populations, probably as the result of a disaster or other event that shrinks the population and therefore the gene pool.
But the Neolithic Y-chromosome bottleneck, as it is known, has been something of a puzzle since its discovery in 2015. This is because it was only observed on the genes on the Y chromosome that get passed down from father to son – which means it only affected men.
This points to a social, rather than an environmental, cause, and given the social restructures between 12,000 and 8,000 years ago as humans shifted to more agrarian cultures with patrilineal structures, this may have had something to do with it.
More here. [Thanks to Steven Pinker.]