The gemara (Baba Basra 109b) councils that one should try to marry “tovim”, someone who comes from “good” stock. The gemara contrasts Moshe Rabeinu, who married the daughter of Yisro, a converted idolater, and who ended up having a grandchild who was an idolatrous priest, with Ahron, who married the daughter of Aminadav and ended up having Pinchas as a grandchild.
I am perplexed by this whole discussion. Does behavior and attitude function like a recessive gene? Neither my wife not I have red hair, but my daughter does – could she also grow up exhibiting some behavior or attitude we don’t teach at home solely as a result of having some genetic mix from past generations? The Derashos haRan actually does offer such an idea to explain why Avraham insisted that Yitzchak marry a wife from his own family rather than any neighboring tribe who had become monotheistic and who were within his sphere of influence. The Ran says that Avraham’s family possessed “genes” of chessed which outweighed the commitment arrived at intellectually by those who surrounded him. I would chalk this idea up to misunderstood genetics, much like other explanations for mitzvos the rishonim offered (e.g. easting kosher is not healthful) which in hindsight we may find lacking or incorrect – if you choose to fit Torah into a “rationalist” framework, that understanding always needs refinement based on changes in secular knowledge.
Interestingly, when the Rambam formulates the gemara’s principle (end of Hil Issurei Biya) it sounds more like a moral idea – the Rambam warns of marrying a daughter of an ignoramus because one’s wife will be uneducated and will not be able to properly educate her children (the Rambam echoes a gemara in Pesachim but the Ein Mishpat on Baba Basra cites it on this sugya). This lesson contains a kernel of truth, but I fail to see how it emerges from our gemara. Yisro is a heroic figure – someone whose life was dedicated to the pursuit of truth until joining the Jewish people. His grandchildren were raised in the home of Moshe Rabeinu, the greatest prophet and teacher of Torah the Jewish people have ever had. Moshe’s grandchildren certainly came from a home steeped in Torah values and Torah wisdom. Yet, the punchline seems to be that because their grandfather once served as an idolatrous priest, that taint carries through the generations.
Should one walk away from this gemara (this would be a good topic for my wife’s blog) with practical shidduch advice? If someone like R’ Elyashiv’s daughter was a prospective shidduch to your son, and her grandfather was a convert who himself now is immersed in Torah learning, would it make sense to walk away from that match and say that all the piety and Torah learning is irrelevant because once-upon-a-time that girls grandfather was a non-Jewish idolater? I find that very hard to believe. If not to be taken literally, what is the moral or philosophical idea one should glean from this Chazal?