#population bottleneck

This is the first time geneticists have analyzed ancient Ashkenazi Jewish DNA in a peer-reviewed paper, because there are ethical prohibitions against unsettling Jewish graves.

Other inferences about the genetic history of the population have been made through sequencing of Ashkenazi Jewish individuals who are still alive. That's how researchers made their initial projections about the bottleneck event.

"There is information about the past by looking at DNA today, but it's not as good as looking at DNA from the past," said Thomas. "It's always gonna be better to have DNA directly from that time. It's the same if you're looking at population history, if you're trying to look, for example, for signatures of natural selection. We can detect it from modern data, but there's nothing more powerful than detecting it from ancient DNA data."

Because the researchers did not know anything about the bodies when they began their research, in this instance, it was acceptable.

"In our case, we didn't disturb any Jewish graves," Thomas said. "These were in soil from excavations from a shopping center development, and we would not have known that they were likely Jewish without our work."

Scientists from Erfurt have published a pre-print paper with genetic data from 33 Ashkenazi Jewish people from the 14th century. The paper hasn't been peer-reviewed, but they say they also observed disease variants associated with Ashkenazi populations.

Although this research does not explain how the 17 people died, nor when the bottleneck took place or how, it does help disprove at least one theory about the origins of Ashkenazi Jews: That they descended from the Khazars, a Turkic people who migrated into Europe in the 12th and 13th centuries when their empire was collapsing.

The theory was put forward by Arthur Koestler in his 1976 book The Thirteenth Tribe.

"That's not going to be true. There's no way you could explain our data on Ashkenazi Jews with that theory, it just doesn't work. So, that's out of the window," said Thomas.

That's because this UK data comes from much earlier.

2002 A low level of genetic variation in mammalian populations where the census population size is relativelylarge has been attributed to various factors, such as a naturally small effective population size, historicalbottlenecks and social behaviour. The killer whale (Orcinus orca) is an abundant, highly social species withreduced genetic variation. We find no consistent geographical pattern of global diversity and no mtDNA variation within some regional populations. The regional lack of variation is likely to be due to the strict matrilineal expansion of local populations. The worldwide pattern and paucity of diversity may indicate a historical bottleneck as an additional factor.