1) THE SOURCE THAT A DAUGHTER EXEMPTS HER MOTHER FROM "YIBUM"
QUESTION: The Gemara assumes that a son and daughter share the Halachic distinction of exempting their mother from Yibum. This means that when a man dies with either a son or a daughter, his wife does not fall to Yibum.
TOSFOS (DH Keivan) and other Rishonim are perplexed by this assumption. The verse explicitly states that Yibum is performed when a man dies "u'Ven Ein Lo" -- "and he has no son" (Devarim 25:5). If he has a son, then his widow is not exempt from Yibum. The verse clearly implies that if he has a daughter, then his widow is not exempt from Yibum. What is the basis for the Gemara's assumption that a daughter also exempts the widow from Yibum?
(a) The RASHBAM (DH Bein) writes that the Gemara understands that the verse of "Ein Lo" means "Ayin Alav" -- "look into him." This teaches that if the man has any child, even a daughter, his widow is exempt from Yibum. This indeed is how the Gemara in Yevamos (22b) understands the verse.
TOSFOS questions the Rashbam's explanation. The Gemara in Yevamos states that the verse of "Ayin Alav" teaches that Beis Din should check even to see if the dead man has a child who is a Mamzer, for even a Mazmer-son will exempt the widow from Yibum. Since "Ayin Alav" is already used to teach that even a Mamzer exempts the widow from Yibum, how can the same Derashah be used to teach that even a daughter exempts the widow from Yibum? Tosfos answers that "Ayin Alav" means that Beis Din must make sure that the deceased has no progeny at all. Accordingly, the same Derashah indeed teaches that both a Mamzer and a daughter exempt a widow from Yibum.
The RASHBA rejects this explanation. He argues that the Derashah of "Ayin Alav" refers explicitly to the subject of the verse -- a son. "Ayin Alav" means that Beis Din must ascertain that the deceased man has no living son (even a Mamzer) before the widow may do Yibum. It does not mean that Beis Din must ascertain that he had any children whatsoever.
(b) The RASHBA therefore cites an opinion which explains that the Gemara's assumption is derived from the verse, "And his name will not be erased from Yisrael" (Devarim 25:6). This teaches that as long as there is a living remembrance for the father's name, even a girl, there is no requirement of Yibum or Chalitzah. (Y. MONTROSE)
2) AGADAH: THE LINEAGE OF PINCHAS
OPINION: The Gemara states that a person should make every effort to marry into a good family. Moshe Rabeinu, who married the daughter of Yisro, had a grandson who was an attendant ("Shamash") for Avodah Zarah. His brother, Aharon, on the other hand, who married the daughter of Aminadav, had a grandson, Pinchas, who defended the honor of Hash-m. The Gemara asks that Pinchas was also a descendant of Yisro, since his father, Elazar (the son of Aharon), married a daughter of "Puti'el," a reference to Yisro who used to "fatten (Pitem) Korbanos for Avodah Zarah." The Gemara suggests that "Puti'el" is not a reference to Yisro, but rather to Yosef, who fought ("Pitpet") against his Yetzer ha'Ra. The Gemara responds that it is apparent that "Puti'el" refers to Yisro from the fact that the Jewish people scorned Pinchas for killing a Nasi while his grandfather was "Puti'el" -- "the fattener." The Gemara answers that although it is true that Pinchas had a maternal grandparent from Yisro, but that grandparent's spouse was from Yosef.
How does the Gemara answer its question?
(a) The RASHBAM (DH Ela) explains that the Gemara means that Pinchas was quite removed from Yisro. The Gemara earlier mentions the fact that Pinchas was also descended from Yosef. This means that Elazar, the son of Aharon, married a woman who was the offspring of a marriage between a descendant of Yosef and a descendant of Yisro. It is possible that she was a third-generation descendant from a daughter of Yisro, which would make Pinchas a fourth-generation descendant. Accordingly, the Gemara's original statement that a person should marry into a good family still applies, because only the children or grandchildren of a bad family are deemed "at risk" to have a predisposition for evil. Generations which are further removed are not affected by the bad family of their ancestry.
(b) TOSFOS (DH Ela) gives a different explanation. He explains that the Gemara specifically says that Pinchas' relation to Yisro was through a maternal grandparent. The Gemara means that only when the father is the product of a marriage from a bad family is there potential for a negative effect on the children.
The MAHARSHA takes issue with these explanations. If the Gemara's answer is as the Rashbam explains it, then why does the Gemara need to mention that one grandparent was from Yosef? It should answer merely that the grandparent from Yisro was too far removed to have any negative effect on Pinchas! Similarly, according to Tosfos' explanation, why does the Gemara not merely say that Pinchas was from a bad family only through his mother?
(c) The MAHARSHA therefore explains that the Gemara intentionally emphasizes that although Pinchas had one maternal grandparent from Yisro, the spouse of that grandparent was from Yosef. The Gemara means that when, in a marriage, one spouse comes from a good family and the other from a bad family, the effects of each family cancel each other out, and the new family (the marriage) is considered neutral. Accordingly, Pinchas' mother's side was neutral, while his father's side, that of Aharon ha'Kohen, was exceptional. Such a marriage was considered a proper and praiseworthy match, and an excellent beginning for raising a Tzadik, as the Gemara states. Although Moshe Rabeinu was a great Tzadik, his partner in marriage was Tziporah, the daughter of Yisro. Accordingly, Moshe's grandson, Yehonasan, had a father who was deemed "neutral." However, his mother might not have been from a good family, which would tip the scale towards having a bad child. This is why the Gemara goes out of its way to show that Pinchas' maternal grandparents were split between Yosef and Yisro. (See IYUN YAKOV who agrees with the Maharsha's explanation, but also defends the explanations of the Rashbam and Tosfos.)
The Maharsha concludes with an important point. Lineage alone does not dictate whether the children will be Tzadikim or Resha'im. Lineage is merely one factor among many other factors. (Y. MONTROSE)