Wasn't yakov born under the same mazal...they were twins. What became of him? Mohel? (his sons must have done that at Shechem) Shochet?
Rabbi Ed Goldstein, woodmere ny
Yakov and Esav were not necessarily born under the same Mazal. The Mazalos take other paths other than the monthly one; there is a Mazal over each hour and day as well -- see Shabbos 156a ("Lo Mazal Yom Garem, Ela Mazal Sha'ah Garem"). Accordingly, they did not have to be born under the same Mazal (since they were not born at the exact same moment).
Y. Tavin
Account must be taken of the principle of Ein Mazal l'Yisrael. See Rashi and Tosfos in Shabbos 156a and numerous authorities both there and in Moed Katan 28a. See also Maharsha in Moed Katan there and Tosfos in Nidah 16b (DH ha'Kol).
Even before Matan Torah, Yakov would have followed this path of Ein MAzal l'Yisrael (see Rashi who writes, "d'Al Yedei Tefilah u'Zechus Mishtaneh Mazalo l'Tovah.")
However, there is an interesting Or ha'Chaim in Toldos (Bereishis 25:23). He writes that "this pregnancy [of Yakov and Esav] was different from all other pregnancies. In a normal pregnancy with twins, the two will be at peace with each other, and their natures will be equal, as the verse says (Shir ha'Shirim 4:5), 'Te'omei Tzeviyah,' and they will dwell in the womb together. Rivka's pregnancy, though, was different, the reason being because 'there are two nations in your womb'.... All of this would not have caused them to fight in the womb if they were of one disposition, as is the nature of twins, but rather they were different from the nature of twins. This is the meaning of the verse, 'mi'Me'ayich Yiparedu,' which does not say 'b'Me'ayich...,' to teach that they were separated and different already from within the womb." (See there.)
We see that Yakov and Esav were the exception. Most twins have the same characteristics (interestingly, the Midrash Rabah to last week's Parshah (Shemos 2:5) states: Rebbi Yanai said, "These twins -- if one had an ache in his head, the other would feel it." Similarly, see Shir ha'Shirim Rabah to Shir ha'Shirim 4:5).
The Chizkuni (to Bereishis 25:24) explains that the word "Tumim" is written here without the Alef, "because all other Te'umim, twins, are similar to each other, but here, one was hairy and one was smooth; Esav was born uncircumcised, and Yakov was born with a Milah; one was red in color and the other was handsome; Esav is compared to a Chazir, and Yakov is compared to a Seh. Why, then, were they born as twins? Because there is no grain without straw."
Thus, it is clear that the situation of the birth of Yakov and Esav was completely exceptional for various reasons.
Joseph Pearlman