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Tissue-Typing in order to Discount Mamzerus

Question: In one of the countries hostile to Jews the Jewish pop-
ulation dwindled until only a handful of Jews remained, out of a
former population of tens of thousands. In one family there were
four brothers: Reuven, Shimon, Levi and Yehudah. Reuven married
and died leaving a son. Owing to their lack of halachic knowledge
and the dearth of rabbinical authority in the country Shimon mar-
ried Reuven’s widow, who was utterly forbidden to him. [No yibum
was mandated because Reuven had left a son.] Reuven’s widow bore
Shimon a son who was named Yemuel. The entire family was rescued
from that hostile land and settled in Eretz Yisrael. Yemuel went to
learn in yeshiva and there he discovered that he was a mamzer and felt
his world cave in. Yemuel had an elderly grandmother named Leah,
whose life was drawing to an end. Just before she died she gathered
her three sons and told them in all honesty that Shimon, who until
then had been considered her son, was actually the child of another
couple who had been murdered by the enemy. She had taken him into
her home when he was a year old, keeping the entire story a secret so
as to avoid reprisal by the enemy. Now, before dying, she was revealing
the secret that Shimon was her adopted son. The grandmother was
entirely ignorant of other developments and of Yemuel’s anguish and
told her story in all innocence. According to the grandmother’s story
Yemuel is not a mamzer.

Shimon and his son Yemuel underwent tissue-testing and the
results confirmed Grandmother Leah’s story that Shimon had been
adopted and was not Reuven’s brother. This would mean that Yemuel
was not a mamzer and could marry a Jewish woman. The question
arises: Can the grandmother’s story and the tissue-typing, both of
which attest that Yemuel is not a mamzer be relied upon?

Response: I presented this question to my father-in-law Rav Y.S.
Elyashiv zt”l, who said that although the Rashash’s comments (Bava
Basra, ibid.) imply that the test may be reliable, according to the

Reliability of Medical Testing for Paternity 2 119