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  • Avrohom Jacobson

A Heavy Tree

A team of scientists assembled a family tree consisting of 13 million people, spanning 11 generations. The data was comprised from, a social genealogy site. "This new database is the largest scientifically validated family tree based on publicly available information," says Yaniv Erlich, a data scientist and computational biologist at the NY Genome Center.

To build thorough genealogies by hand is extremely time- consuming and challenging, which is why crowdsourced information was so valuable in this research. It allowed for a much larger range of data sources. The team, in fact, assembled 5.3 million family trees, with the largest being the 13 million person set.

Testing the utility of the family tree, the researchers used it to investigate migration, marriage, and the influence of heredity on longevity. They found that married couples were, on average, fourth cousins between 1650 and 1850, by comparing the couples birthplaces to their familial relationship.

They also discovered that although the rise of railroad travel in the early 1800’s increased the distance between couples birthplaces, couples were actually closer related in those first few decades. Familial relatedness only declined in the following decades. This is despite theories in evolution studies which suggest that the farther apart spouses are born, the lower their genetic relatedness will be. Based on their data, they concluded that it was cultural changes, rather than transportation changes that led to the decrease in cousin marriages.

Through analyzing three million pairs of relatives, the researchers also found that although it is commonly cited that 25% of longevity is hereditary, the actual number is closer to 16%.

So What?

At Peddlers and Parchments, we are always looking for ways of employing Data Science and Machine Learning in service of princely genealogy. Do the researchers' discoveries widely hold true or do the unique circumstances and customs in rabbinic families dictate results distinct from these findings?

One very strong theme that permeates the lives of members of rabbinic families is the emphasis on marriage in general, and inbreeding in particular. In the Bible, Numbers 36:5-13, Moses tells the daughters of Zelophehad to marry within their tribe, and indeed, all five daughters marry their cousins.

We also see in the Talmud, Tractate Yevamot 62b, that the Sages encourage the marriage between an uncle and a niece. So the question arises, does the marriage data from the research reflect what went on in rabbinic families?

To quote a renowned expert on the subject, Neil Rosenstein, the author of ‘The Unbroken Chain’ and The Lurie Legacy, “In Rabbinic families in particular, the cousin relationship was often much closer, first cousins being the norm, as well as uncles marrying nieces. Not only that, but often weddings were carried out a week later during the same visit from the other town.”

So while on average, married couples from the collected data were fourth cousins, the average was drastically different for rabbinic families. Couples had a much closer genetic relation. Rosenstein also weighed in on the railroads' affects on familial relation in marriage: “Rabbinical families knew no geographic borders, so that distance did not play a role. The arranged marriages limited the diversity of the gene pool.” So even the rise of railroad travel didn't change the existing conditions of marriage within rabbinic families, because distance and borders were not a deterrent to begin with.

It is quite obvious that although the new data collected by the research team is immense and extremely valuable, the uniqueness of rabbinic genealogy requires its own specialized research.


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