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https://arstechnica.com/science/2018/02/prehistori...

“The two studies published this week approximately double the size of the entire ancient DNA literature and are similar in their sample sizes to population genetic studies of people living today,” Harvard Medical School geneticist David Reich, who coordinated the studies, told Ars. “We can pick out subtleties in ancient demographic process that were more difficult to appreciate using the small sample size studies available before.”

he Bell Beaker culture, for example, left behind stylized bell-shaped pots, along with copper daggers, perforated buttons, stone wrist guards, and arrowheads. These bell-shaped pots first turned up in Spain around 4,750 years ago, and they had spread throughout Central and Western Europe and Northwest Africa by about 4,500 years ago, largely replacing local styles of pottery. By 4,300 years ago, Bell Beaker artifacts began appearing in Britain, replacing artifacts associated with the culture that built Stonehenge.

it’s hard to tell if that happened because the people who made the Bell Beaker artifacts swept in and wiped out the earlier culture or if it happened because people saw Bell Beaker artifacts and decided to copy them. Both processes look pretty much the same in the archaeological record that’s currently available, but they’re very different versions of human history.

And the answer, according to the genomes of 400 prehistoric people from Britain, Iberia, and Central Europe, is that both versions of the story happened in different parts of Europe.

An even larger mass migration brought agriculture into Europe about 8,000 years ago, when farmers from Anatolia moved north and west into Europe, mostly following the Danube River and the Mediterranean coastline. That’s not a new idea, but genomic data adds some surprising detail to the story, described in a second study of 225 sets of ancient European remains, dating from 14,000 to 2,500 years ago.

The incoming population from Anatolia almost completely replaced the previous residents of Southeastern and Central Europe within centuries of their arrival. This wasn’t a mere cultural shift; it was a nearly complete population turnover.

“It’s not clear how these movements happened—whether by disease, or by violence, or by some kind of biased intermarriage process—but what the genetics shows unambiguously is that these changes did happen and much more dramatically than any archaeologists expected,” said Reich. But the genomic data offers some hints about how that population turnover may have played out, and it may actually have happened a little differently everywhere two groups of people interacted.

For instance, the northward spread of farming stopped for several thousand years at the boundary of the latitudes where most crops grow well; archaeologists knew that based on earlier finds. What the genomic study reveals is that along that boundary, in Northern Europe, genes associated with earlier hunter-gatherer groups tended to show up more on Y-chromosomes than X-chromosomes, which implies that males were passing on hunter-gatherer ancestry more than females. That’s a hint that women from farming communities tended to marry into hunter-gatherer communities, but not necessarily the other way around.