Rabbi Heller's Blog

A construction project in a small German town, has shed new light on the Jewish legacy that can be carried, quite literally, in our bones and our blood.  In 1453, the Jewish community of Erfurt was exiled, bringing an end to several hundred years of Jewish presence. A storehouse was built over the centuries-old Jewish cemetery. Recently, that storehouse was renovated to serve as a parking deck, and 47 of the original graves were uncovered.  Genetic research performed on the remains offers new insights into how we are related, and how we have been affected by history.

Jews have been concerned about genetics for a long time, going back to the Torah itself, and the portion we read this week.  In Vayetze, Jacob is offered the opportunity to create his own herd by taking the least valuable of the flocks of his father-in-law Laban and breeding them to create a healthy herd.    At face value, the telling of the story seems to conflict with modern genetic science:  showing colored rods to the sheep during the mating season will not change the color of their offspring.  In fact, a more careful reading of the text shows that Jacob may have been making use of centuries-old breeding techniques to increase the chances of certain traits being passed on within  his flock.  

However, our relationship with genetics has also been quite complex.  Germany was the backdrop to one of the most infamous attempts to portray Jews as genetically inferior.  Jews themselves must occasionally be reminded that there are Jews of many colors and shapes, that being Jewish is about one’s commitment to a tradition, not one’s racial or regional origins, let alone connection to a particular Ashkenazi branch.   Attempts to connect Cohen status to genetic traits, or to define a child’s Jewish status based on genetic testing, are fraught with potential dangers.

The relationship is particularly complicated for Ashkenazi Jews. We share a very high proportion of genetic material because our ancestors went through what are called “genetic bottlenecks”, where a  population originated from a relatively small set of ancestors.  Ashkenazi Jews tended to live in small, isolated communities that originated from just a few families, and there were often plagues and massacres that wiped out whole communities, leaving just a few to restore our numbers in a region.  As a result of this “shallow gene pool,” Ashkenazi Jews are prone to a set of over 20 genetic diseases, of which Tay-Sachs is one of the most well-known.  Projects like www.jscreen.org help people who are starting Jewish families to find ways to avoid the potential negative impact of these diseases.

This particular research was not without its controversy.  Normally, Jewish law prohibits disturbing a grave or using the body of the deceased for abstract research, but in this case, the bodies had already been disturbed, and scientists were able to obtain DNA with minimal disruption, including by drawing it from teeth.

The results of the research are complex, but one easy-to-understand observation is that the community already had many key genes in common with Ashkenazi Jews today, but was more diverse than Ashkenazi communities today. In fact, the medieval Jewish community in Erfurt actually came from two different locations, and both populations shared common ancestors dating back even earlier, but many of these Jews did not leave modern descendants.  This discovery has important historical implications. Until recently, many scientists thought that the genetic bottlenecks that resulted in our common ancestry took place 600-800 years ago, but this research determined that our common ancestry dates back even further, and gives insights into the challenges faced by these Jewish communities.

Jacob understood that genetics alone do not define us. He and Esau had the same parents but grew into very different people, and he was able to get flocks from the same herd to develop in very different directions. We know much harm has come to the world by those who would define a person’s value by their genetic makeup. We believe that DNA is not destiny, but it is history.   Our genes offer not only a literal genealogy of our ancestors, but also a map of their journeys and a reminder of the miracles of their survival when others perished.  Every one of our cells carries a ledger of the lives of those who came before us.