Does anyone know when the switch the matrilineal descent took place? I've seen other information about the potential impetus, but when did it become so? Was there even a switch?
While Jewish law applies patrilineal descent to other nations (Yevamos 78b), Nachmanides writes that matrilineal descent applied to the Jewish people from the time of Avraham and onwards (Commentary to Vayikra 24:10). This is justified by the existence of some degree of Israelite nationhood from the time of the Patriarchs, which is suggested by the Talmud's reference to Esav as legally an Israelite (Kiddushin 18a).
However, Nachmanides also cites the French rabbis as being of the opinion that the switch from patrilineal to matrilineal descent occurred at the time of the giving of the Torah at Mount Sinai. This opinion interprets the Midrash (Sifra on Emor, 14:1), which writes that the "son of the Israelite woman" converted, as implying that anyone born before the giving of the Torah who was not a member of the Children of Israel via patrilineal descent needed to convert. This is different from the conversion-type rituals that the other Israelites performed at Mount Sinai (Kerisus 9a), which formalized their de facto status.
The only three good examples I can think of are Abraham, who's mother could not have been Jewish because technically Judaism did not exist before the covenant. Even if Abraham's mother converted, would it have counted, since she was not Jewish at the time of birth? Second, Zipporah, Moses' wife, was a Midianite, not a Hebrew. While the children of Moses were not chosen as his successor, it wasn't because of their mother, but because they idled instead of studying Torah. Joseph also married out of the tribe, to an Egyptian woman, who was certainly not Jewish. However, Ephraim and Menassah became to lead two of the tribes of Israel, so they must have certainly been considered Jewish? I know the Mishna is the beginning of matrilineality, but where does it originate from or gather justification from? I'm not trying to deny matrilineality (although by that standard I am not a Jew), but play the devil's advocate and seek some answers to these examples. I don't have enough rep to comment yet :(