The Cohen / DNA Connection
The fascinating story of how DNA studies confirm an ancient biblical tradition.
Dr. Karl Skorecki, a Cohen of Eastern European parents, was attending synagogue one morning. The Cohen called up for the Torah reading that morning was a Jew of Sephardic background, whose parents were born in North Africa. Dr. Skorecki looked at the Sephardi Cohen’s physical features and considered his own physical features. They were significantly different in stature, skin coloration and hair and eye color. Yet both had a tradition of being Cohanim, direct descendants of one man—Aaron, the brother of Moses.
Cohanim (plural of Cohen) are the priestly family of the Jewish people, members of the Tribe of Levi. The books of Exodus and Leviticus describe the responsibilities of the Cohanim, which include the Temple service and blessing of the people. The Torah (the first five books of the Bible) describes the anointing of Aaron, the brother of Moses, as the first High Priest (Cohen Gadol).
Jewish tradition, based on the Torah, is that all Cohanim are direct descendants of Aaron, the brother of Moses. The Cohen line is patrilineal—passed from father to son without interruption for 3,300 years, or more than 100 generations.
Dr. Skorecki considered, “According to tradition, this Sephardi Cohen and I have a common ancestor. Could this line have been maintained since Sinai, and throughout the long exile of the Jewish people?” As a scientist, he wondered, could such a claim be tested?
Being a nephrologist and a top-level researcher at the University of Toronto and the Rambam-Technion Medical Center in Haifa, he was involved in the breakthroughs in molecular genetics which are revolutionizing medicine and the study of the life-sciences. He was also aware of the newly developing application of DNA analysis to the study of history and population diversity.
Dr. Skorecki considered a hypothesis: if the Cohanim are descendants of one man, they should have a common set of genetic markers—a common haplotype—that of their common ancestor. In our case, Aaron HaCohen.
HOW IT WORKS
A genetic marker is a variation in the nucleotide sequence of the DNA, known as a mutation. Mutations which occur within genes—a part of the DNA which codes for a protein—usually cause a malfunction or disease and is lost due to selection in succeeding generations. However, mutations found in so-called “non-coding regions” of the DNA tend to persist.
Since the Y chromosome consists almost entirely of non-coding DNA (except for the genes determining maleness), it would tend to accumulate mutations. Since it is passed from father to son without recombination, the genetic information on a Y chromosome of a man living today is basically the same as that of his ancient male ancestors, except for the rare mutations that occur along the hereditary line.
A combination of these neutral mutations, known as a haplotype, can serve as a genetic signature of a man’s male ancestry. Maternal genealogies are also being studied by means of the m-DNA (mitrocondrial DNA), which is inherited only from the mother.
THE SEARCH BEGINS
Dr. Skorecki made contact with Professor Michael Hammer, of the University of Arizona, a leading researcher in molecular genetics and a pioneer in Y chromosome research. Professor Hammer uses DNA analysis to study the history of populations, their origins and migrations. His previous research included work on the origins of the Native American Indians and the development of the Japanese people.
A study was undertaken to test the hypothesis. If there were a common ancestor, the Cohanim should have common genetic markers at a higher frequency than the general Jewish population.
In the first study, as reported in the prestigious British science journal, Nature (January 2, 1997), 188 Jewish males were asked to contribute some cheek cells from which their DNA was extracted for study. Participants from Israel, England and North America were asked to identify whether they were a Cohen, Levi or Israelite, and to identify their family background.
The results of the analysis of the Y chromosome markers of the Cohanim and non-Cohanim were indeed significant. A particular marker, (YAP-) was detected in 98.5 percent of the Cohanim, and in a significantly lower percentage of non-Cohanim.
In a second study, Dr. Skorecki and associates gathered more DNA samples and expanded their selection of Y chromosome markers. Solidifying their hypothesis of the Cohens’ common ancestor, they found that a particular array of six chromosomal markers was found in 97 of the 106 Cohens tested. This collection of markers has come to be known as the Cohen Modal Hapoltype (CMH)—the standard genetic signature of the Jewish priestly family. The chances of these findings happening at random is greater than one in 10,000.
The finding of a common set of genetic markers in both Ashkenazi and Sephardi Cohanim worldwide clearly indicates an origin pre-dating the separate development of the two communities around 1000 CE. Date calculation based on the variation of the mutations among Cohanim today yields a time frame of 106 generations from the ancestral founder of the line, some 3,300 years—the approximate time of the Exodus from Egypt, the lifetime of Aaron HaCohen.
Professor Hammer was recently in Israel for the Jewish Genome Conference. He confirmed that his findings are consistent—over 80 percent of self-identified Cohanim have a common set of markers.
The finding that less than one-third of the non-Cohen Jews who were tested possess these markers is not surprising to the geneticists. Jewishness is not defined genetically. Other Y-chromosomes can enter the Jewish gene pool through conversion or through a non-Jewish father. Jewish status is determined by the mother. Tribe membership follows the father’s line.
Calculations based on the high rate of genetic similarity of today’s Cohanim resulted in the highest “paternity-certainty” rate ever recorded in population genetics studies—a scientific testimony to family faithfulness.
Stated Dr. David Goldstein of Oxford University:
“For more than 90 percent of the Cohens to share the same genetic markers after such a period of time is a testament to the devotion of the wives of the Cohens over the years. Even a low rate of infidelity would have dramatically lowered the percentage.”
[Science News, October 3, 1998]
Wider genetic studies of diverse present day Jewish communities show a remarkable genetic cohesiveness. Jews from Iran, Iraq, Yemen, North Africa and European Ashkenazim all cluster together with other Semitic groups, with their origin in the Middle East. A common geographical original can be seen for all mainstream Jewish groups studied.
This genetic research has clearly refuted the libel that the Ashkenazi Jews are not related to the ancient Hebrews, but are descendants of the Kuzar tribe—a pre-10th century Turko-Asian empire which reportedly converted en masse to Judaism. Researchers compared the DNA signature of the Ashkenazi Jews against those of Turkish-derived people, and found no correspondence.
OTHER SURPRISING FINDINGS
In their second published paper in Nature (July 9, 1998) the researchers included an unexpected finding. Those Jews in the study who identified themselves as Levites did not show a common set of markers as did the Cohanim. The Levites clustered in three groupings, one of them the CMH. According to tradition, the Levites should also show a genetic signature from a common paternal patrilineal ancestor. The researchers are now focusing effort on the study of Levites’ genetic make up to learn more about their history in the Diaspora.
Using the CMH as a DNA signature of the ancient Hebrews, researchers are pursuing a hunt for Jewish genes around the world.
This could have ramifications in the search for the Biblical Ten Lost Tribes.
Using the genetic markers of the Cohanim as a yardstick, these genetic archaeologists are using DNA research to discover historical links to the Jewish people.
The researchers’ policy is that the research is not a test of individuals, but an examination of the extended family. Having the CMH is not a proof of one’s being a Cohen, for the mother’s side is also significant in determining one’s Cohen status. At present, there are no ramifications in Jewish law due to this discovery. No one is certified nor disqualified because of their Y chromosome markers.
The research has shown a clear genetic relationship amongst Cohanim and their direct lineage from a common ancestor. The research findings support the Torah statements that the line of Aaron will last throughout history:
“... and they shall have the Priesthood as a statute forever, and you shall consecrate Aaron and his sons.” [Exodus 29:9]
“... it shall be for them an appointment to an everlasting Priesthood throughout their generations.” [Exodus 40:15]
“And it shall be to him and to his descendants after him a covenant of everlasting Priesthood.” [Numbers 25:13]
That our Torah tradition is supported by these findings is an inspiration for many that God surely keeps His promises. May we soon see the Cohanim restored to their service, Levites on their Temple platform and Israelites at their places.