In a genetic study conducted in 2002, scientists found that 40% of all living Ashkenazi Jews—some 3.5 million—trace their DNA back to 4 “founding mothers” who lived in Central and Eastern Europe over 1,000 years ago.
The scientists studied the mitochondrial DNA (otherwise known as mtDNA) of 11,000 women of Ashkenazi origin living in 67 different countries. Four distinct strands of mtDNA were found in each of the study’s participants, indicating shared maternal ancestry. What’s more, this genetic signature appears almost exclusively in Ashkenazi Jews (with occasional occurrence in Sephardic Jews, as well).
As far as Ashkenazi oddities go, that’s not all: a 2010 study on Jewish ancestry found that any 2 Ashkenazi Jews shared roughly as much DNA as 4th or 5th cousins, giving a whole new meaning to the phrase “member of the tribe.”