In 2006, a study by Behar et al., based on what was at that time high-resolution analysis of haplogroup K (mtDNA), suggested that about 40% of the current Ashkenazi population is descended matrilineally from just four women, or "founder lineages", that were "likely from a Hebrew/Levantine mtDNA pool" originating in the Middle East in the 1st and 2nd centuries CE. Additionally, Behar et al. suggested that the rest of Ashkenazi mtDNA is originated from ~150 women, and that most of those were also likely of Middle Eastern origin. In reference specifically to Haplogroup K, they suggested that although it is common throughout western Eurasia, "the observed global pattern of distribution renders very unlikely the possibility that the four aforementioned founder lineages entered the Ashkenazi mtDNA pool via gene flow from a European host population".

A 2006 study by Behar et al, suggested that what percentage of the current Ashkenazi population was descended from "founder lineages"?