Y-chromosomal Aaron

Y-chromosomal Aaron is the name given to the hypothesized most recent common ancestor of the patrilineal Jewish priestly caste known as Kohanim (singular Kohen, also spelled Cohen). According to the traditional understanding of the Hebrew Bible, this ancestor was Aaron, the brother of Moses. Historical-critical reading of the biblical text suggests that the origin of the priesthood could have been much more complex, and that for much if not all of the First Temple period, Kohen may have not (necessarily) been synonymous with "Aaronide". Rather, this traditional identity seems to have been adopted sometime around the Second Temple period.

The original scientific research was based on the hypothesis that a majority of present-day Jewish Kohanim share a pattern of values for six Y-STR markers, which researchers named the extended Cohen Modal Haplotype (CMH). Subsequent research using twelve Y-STR markers indicated that nearly half of contemporary Jewish Kohanim shared Y-chromosomal J1 M267 (specifically haplogroup J-P58, also called J1c3), while other Kohanim share a different ancestry, such as haplogroup J2a (J-M410).

While these genetic studies were seen as possibly supporting the traditional biblical narrative, subsequent research (by the original researchers and others) has challenged this conclusion in a number of ways and has in fact shown that the genealogical record "refutes the idea of a single founder for Jewish Cohanim who lived in Biblical times", and rather "seems to vindicate the historical-critical hypothesis of competing priestly clans."