Jewish Genes And Converts – OpEd


Most Jews trace a considerable or even a majority (at least 50–60%) of ancestral component clearly identified with the populations from Late Bronze Age and Iron Age Southern Levant, where Judah and Israel were located among other Canaanite-derived groups, e.g. Moabites and Edomites.

Unless two populations came from very different homelands and historic backgrounds, you just can’t genetically differentiate closely related populations living in the same region and mostly divided by religion and tribal/ethnic allegiance (culture and politics), not by starkly separate and isolated origins.

Obviously the original 12 tribes as described in the Hebrew Bible, assimilated neighboring people and tribes and admixed with them (books written by the ancient Jews describe inter-ethnic marriages), so the Southern Levantine ancestry in Jews can be best tied to after the end of that tribal stage, in the late Iron Age when conversion to Judaism became more frequent. 

A few relatively minor groups of Jews, such as Ethiopian, Yemeni and Cochin Jews, do appear to have little (not zero, but little, say under 20%) genetic admixture from ancient Southern Levantines (most of their ancestors were converts to Judaism in Antiquity).

Those ancient Southern Levntines are close to the present-day Samaritans and Christian Palestinians, suggesting theirs are the genetic profile and phenotypic range, still available for us to see them right now, closest to the Israelites and Judeans.

Ironically – and sadly, considering everything that’s going on -, Middle Eastern Jews tend to be more closely related to Muslim Palestinians and, even more so, to Christian Palestinians. Ashkenazi Jews, due to substantial Southern and Eastern European admixture from converts in Roman Empire times, are a bit further, but still among the populations genetically closest and with most ancestry shared with Palestinians, both Christians and Muslims.

A study by Neil Risch, PhD, professor of genetics, statistics, and health research and policy at Stanford University School of Medicine looked at the regional distribution of mutations in Ashkenazi Jews, and the age of those mutations. Dr. Risch found three points in time when mutations entered the population. One mutation has been in the Jewish population for 120 generations – around the time the Jewish people formed a distinct population in the Middle East, sometime prior to the time of King David. 

This mutation causes a type of hemophilia called Factor 11 deficiency type II, and is also found in Sefardic Jews who lived in Muslim countries. Since conversion to Judaism was common from Biblical days to the late Roman period (think of Ruth and the father of Rabbi Akiba) only this mutation remained for so long in the Jewish population. 

The time machine of Jews’ genes may show that most Jews have a shared ancestry that traces back to ancient Palestine but, like all of humanity, Jews are mutts. About 80% of Jewish males and 50% of Jewish females trace their ancestry back to the Middle East. The rest entered the “Jewish gene pool” through conversion or intermarriage. Those who did intermarry often left the faith in a generation or two, in effect pruning the Jewish genetic tree. But many converts became interwoven into the Jewish genealogical line. 

The iconic convert, Ruth, who married Boaz and became the great-grandmother of King David, began as an outsider, but you don’t get much more Jewish than the bloodline of King David!

But we can’t avoid engaging the most challenging questions in the age of genetics. Because of our history of Middle Age endogamy, Jews are a goldmine for geneticists studying human differences in the quest to cure disease.

Ashkenazi Jews have an unusually high risk of several genetic diseases such as Tay-Sachs, Gaucher, Niemann-Pick, Mucolipidosis IV, as well as breast and ovarian cancer. Is this due just to random chance and bad luck; or was it influenced by how many non-Jews were prevented from converting to Judaism, and entering the Jewish gene pool in each generation? 

Jews remain identifiable in large measure by the 40 or so diseases Jews disproportionately carry, the inescapable consequence of inbreeding. A larger number of converts to Judaism during the last 1,500 years would have eliminated most if not all of these Jewish genetic diseases. 

It is true that Ashkenazi Jews tend to marry within their own population, but it is also true that European Jews were prohibited by the Church from seeking or even just accepting converts to Judaism. Both factors contributed to keeping those 40+ genetic diseases mutations common. When Jews were able to openly seek and welcome converts to Judaism, as was true for most of 1.500 years prior to the fifth century BCE, very few genetic diseases continued for many centuries.

As humankind becomes more genetically sophisticated, identity becomes both more fluid and more fixed. Jews in particular can find threads of our ancestry literally anywhere, muddying traditional categories of nationhood, ethnicity, religious belief and “race.” But such discussions, ultimately, are subsumed by the reality of the common shared ancestry of humankind.

The majority of the mutations – including all of the mutations in lysosomal storage genes – entered the population when the Ashkenazi Jews formed a coherent group about 50 generations ago in central and eastern Europe. The final mutations cropped up in the Lithuanian Ashkenazi Jews about 12 generations ago. 

All of these mutations would have been reduced by the entry of non-Jews into the Jewish gene pool through conversion to Judaism. Because conversion was severely restricted by the European Church during  the 4-6th century, converts to Judaism were not able to help eliminate these harmful genetic mutations. 

With the rise of conversion to Judaism in the 20th century, these harmful mutations will substantially decline by the end of this century. So it was not just chance that kept these harmful mutations from being eliminated from the Askenazi Jewish population. Those who prevented non-Jews from becoming Jewish also played a part.

Rabbi Allen S. Maller

Allen Maller retired in 2006 after 39 years as Rabbi of Temple Akiba in Culver City, Calif. He is the author of an introduction to Jewish mysticism. God. Sex and Kabbalah and editor of the Tikun series of High Holy Day prayerbooks.

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