Die Entwicklung der Landwirtschaft, des Staates und des Krieges

[Quintus Fabius]

Mit dem frühesten Ackerbau trat noch eine interessante Nebenwirkung auf: eine drastische Verengung des männlichen Erbgutes, was schlicht und einfach heißt, dass nur noch sehr wenige Männer sich vermehrten, und schlussendlich alle Kinder von ihnen abstammten. Das ganze geht bis zu einem Verhältnis von 17 Frauen auf 1 Mann.

Die Gründe dafür sind noch nicht ganz klar und werden diskutiert. Vermutlich war es ein ganzes Faktorenbündel, zu dem aber schlussendlich auch massive Kriege (in dieser Zeit tauchen die ersten Nachweise von Völkermord und Massakern auf) und die Herrschaft kleiner Kriegereliten massiv beigetragen haben.

https://pmc.ncbi.nlm.nih.gov/articles/PMC4381518/

https://www.sciencealert.com/neolithic-y...neal-clans

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.

In fact, a drop in genetic diversity doesn't mean that there was necessarily a drop in population. The number of men could very well have stayed the same, while the pool of men who produced offspring declined.

This was one of the scenarios proposed by the scientists who penned the 2015 paper.

"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," computational biologist Melissa Wilson Sayres of Arizona State University explained at the time.

Tian Chen Zeng, a sociologist at Stanford, has now built on this hypothesis. He and colleagues point out that, within a clan, women could have married into new clans, while men stayed with their own clans their entire lives. This would mean that, within the clan, Y chromosome variation is limited.

However, it doesn't explain why there was so little variation between different clans. However, if skirmishes wiped out entire clans, that could have wiped out many male lineages - diminishing Y chromosome variance.

Computer modelling have verified the plausibility of this scenario. Simulations showed that wars between patrilineal clans, where women moved around but men stayed in their own clans, had a drastic effect on Y chromosome diversity over time.

This means that warring patrilineal clans are the most likely explanation, the researchers said.