(JNS.org) A new study conducted at Columbia University, based on the genetic sequencing of 128 Ashkenazi Jews, shows that modern Ashkenazi Jews descend from a small group of about 350 individuals who lived between 600 and 800 years ago. Those ancestors of current Ashkenazi Jews were both European and Middle Eastern, said the study, which was published Tuesday, Sept. 9, in the Nature Communications journal. Today’s approximate population of 10 million Ashkenazi Jews descends from such a small group of ancestors due to the “bottleneck” effect, a drastic reduction in population size that occurred for unknown reasons about 25-30 generations ago, according to the study.

“[Among Ashkenazi Jews] everyone is a 30th cousin… They have a stretch of the genome that is identical,” Itsik Pe’er, an associate professor of computer science and systems biology at Columbia University, told Live Science.