Y DNA studies tend to imply a small number of founders in an old population whose members parted and followed different migration paths. In most Jewish populations, these male line ancestors appear to have been mainly Middle Eastern. For example, Ashkenazi Jews share more common paternal lineages with other Jewish and Middle Eastern groups than with non-Jewish populations in areas where Jews lived in Eastern Europe, Germany and the French Rhine Valley. This is consistent with Jewish traditions in placing most Jewish paternal origins in the region of the Middle East. Conversely, the maternal lineages of Jewish populations, studied by looking at mitochondrial DNA, are generally more heterogeneous. Scholars such as Harry Ostrer and Raphael Falk believe this indicates that many Jewish males found new mates from European and other communities in the places where they migrated in the diaspora after fleeing ancient Israel. In contrast, Behar has found evidence that about 40% of Ashkenazi Jews originate maternally from just four female founders, who were of Middle Eastern origin. The populations of Sephardi and Mizrahi Jewish communities "showed no evidence for a narrow founder effect." Subsequent studies carried out by Feder et al. confirmed the large portion of non-local maternal origin among Ashkenazi Jews. Reflecting on their findings related to the maternal origin of Ashkenazi Jews, the authors conclude "Clearly, the differences between Jews and non-Jews are far larger than those observed among the Jewish communities. Hence, differences between the Jewish communities can be overlooked when non-Jews are included in the comparisons."
What tends to imply a large number of founders in an old population?