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Were Yaakov and Esav monozygotic ("identical") twins, or dizygotic ("fraternal") twins?

(Inspired by Sabbahillel's answer to Why is the birth of twins a Chidush for Rivka?)

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  • sort of similar judaism.stackexchange.com/q/4412/759
    – Double AA
    Jan 25 '18 at 1:53
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    I'm not sure why you would ask this. Doesn't the Torah describe each of their features differently? Perhaps, not at the time of birth, per se, but at the time Ya'akov is about to get the blessings he says to Rivka, "My brother is hairy and I am smooth."
    – DanF
    Jan 25 '18 at 3:07
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    Can somebody please explain how ""My brother is hairy and I am smooth."" works for monozygotic twins?
    – Al Berko
    Jan 28 '18 at 0:43
  • @AlBerko see below Jan 28 '18 at 0:51
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  1. Chizkuni (Bereishis 25:25), quoting Rabi Yosi, says that that Esav was conceived by the last drop, and Yaakov by the first drop, and first in is last out. Thus, according to them, they were clearly dizygotic twins, as both eggs must have been fertilized seperately.

  2. Ibn Ezra there (same link) says that there were two שליות (amniotic sacs?) that broke at once, also implying that they were dizygotic twins.

  3. Rav Hirsch (quoted here) claims that they were monozygotic twins, and this was the detail of the pregnancy that shocked Rivkah.

  4. Various modern medical professionals (see here, for example) have concluded that Yaakov and Esav were monozygotic twins, and that this was the first documented case of TTTS. There are various indications from the Parshiyos that indicate this, such as the descriptions of Yaakov and Esav, Yaakov holding Esav's heel etc.

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  • FYI, שליות means "placentae". The singular version of this verse (sort of) is mentioned in Devarim 28:57.
    – DanF
    Jan 25 '18 at 16:04
  • @DanF thanks, I had thought so originally, but I saw some articles translating otherwise. Jan 25 '18 at 16:21
  • How does R' Hirsh and others "monozygotics" explain R' Yossy and ""My brother is hairy and I am smooth."" verse?
    – Al Berko
    Jan 28 '18 at 0:45
  • @AlBerko I think he holds that it either developed later in life, but look it up. Others say because of the TTTS, which leaves one twin more developed than the other. Jan 28 '18 at 0:50

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