Above are illustrated a priest, high priest, and Levite of the Hebrews of Torah times. A priest (kohen) had to descend from Aaron. The first high priest was Aaron, after which the position was to pass to his eldest son, then to his eldest son, ad infinitum (this practice was followed in early Judaism, but altered during later years as the Israelites came to be ruled by foreign powers).

Once in Israel, the Levites (the tribe of Levi, to which Moses and Aaron belonged) were not given land, as they were to perform religious functions for Hebrews throughout Israel (in exchange for which, members of this tribe were paid a tithe; this tithing is still observed among many Orthodox and Hasidic Jews).

Interestingly, modern DNA research has discovered the Cohen Modal Haplotype (CMH), linked back to a person researchers refer to as Y-chromosomal Aaron (after Aaron, the brother of Moses, and as a nod to the Y-chromosomal Adam haplotype famous in archaeogenetics). Further research has revealed that about half of today's Jewish kohanim share a close common ancestor, with 15% of them even more closely related. Although modern science cannot state that this ancestor was the biblical Aaron, it does show that despite the thousands of years that have passed since the Jewish priesthood was organized, a remarkable job appears to have been done at observing the lines of patrilineal descent. Click here to enlarge.