Hi Adam,

I respectfully disagree. We have just begun to scratch the surface of human knowledge. The most sophisticated sages of the past thousand years lacked the tools available today even to amateurs, like fax machines, photocopiers, computers, the Internet, and DNA. Future genealogists, utilizing even more advanced tools we can't conceive of, might well be able to reconstruct the Jewish communities of, say, Mainz or Worms in the year 1040. As Orville Wright remarked in his journal after the Wright brothers' first manned flight at Kitty Hawk in 1903: "How amazing it is that all these secrets have been kept so long, just so we could discover them." 
Best regards,
Dan Rottenberg
Philadelphia PA USA
dan@...

Hi Dan,

This doesn't answer your question about how, but at least it's a start on a bibliography: https://www.encyclopedia.com/religion/encyclopedias-almanacs-transcripts-and-maps/isaac-ben-eliezer

My guess would be that Rashi has been so meticulously studied over the years that if anything had been discovered about his family tree, we would know by now.

--
Adam Cherson,NY, NY
Benyakonski, Kherszon, Rubinovich, Solts, Grodsinski, Levine, Cohen, Kaplan, Lubetski, Karchmer, Horwitz, Rabinovich, Zussman (Lida, Voronova, Dieveniskes, Konvaliski, Smarhon, Vilna)
Genomics Publications and Presentations: https://independent.academia.edu/AdamCherson

In my continuing quest to track the family of Rashi (1040-1105), I came across this unsourced entry from a Rashi biography on the jewage,com site:

"His father was his main Torah teacher until his death when Rashi was still a youth. At the age of 17 he married and soon after went to learn in the yeshiva of Rabbi Yaakov ben Yakar in Worms, returning to his wife three times yearly, for the Days of Awe, Passover and Shavuot. When Rabbi Yaakov died in 1064, Rashi continued learning in Worms for another year in the yeshiva of his relative, Rabbi Isaac ben Eliezer Halevi, who was also chief rabbi of Worms. Then he moved to Mainz, where he studied under another of his relatives, Rabbi Isaac ben Judah, the rabbinic head of Mainz and one of the leading sages of the Lorraine region straddling France and Germany. He returned to Troyes at the age of 25, after which time his mother died,"
I haven't been able to find R. Isaac ben Elizer haLevi or R. Isaac ben Judah in the Jewish Encyclopedia or any other source. Does anyone know who they were and/or how they were related to Rashi (if indeed they were)? 
Many thanks.
Dan Rottenberg
Philadelphia PA USA
dan@...