A recent paper by Marta Costa et al. found that around 80% of Ashkenazi mitochondrial DNA had a prehistoric European origin (and ruled out the Khazar hypothesis). Combined with previous Y chromosome studies indicating that the male line is Middle Eastern, the results suggested a scenario in which Jewish males married European females after traveling to Europe.
Now another paper, by Shai Carmi et al., reinforces this scenario, finding an “even mix of European and Middle Eastern ancestral populations” (“Sequencing an Ashkenazi reference panel supports population-targeted personal genomics and illuminates Jewish and European origins“).
The basic picture is illustrated in the following figure.
The left side of the figure at the top shows Ashkenazi origins in the Middle East (AJ=Ashkenazi Jewish), with a bottleneck around 90,000 years ago. Then around 21,000 years ago a portion of the Middle Eastern group migrated to Europe (FL = the Flemish control group) and, according to the authors, became the predominant European group. After undergoing genetic differentiation in Europe (presumably shaping the modern behavioral and intelligence profile of Europeans), there there was an influx of the FL group to the AJ group within Europe, with 49% of Ashkenazi genes coming from the FL. This was followed by an extreme bottleneck around 700 years ago when the Ashkenazi population dwindled to an effective population size of around 330 people. Read more