If a man has two wives, the one beloved and the one hated, and they bear him sons, the beloved and the hated, and the firstborn son is the hated one’s—
English: “And they bear him sons” — Ameimar said: a tumtum who is later opened and found to be male does not reduce the firstborn’s portion, as it is said “and they bear him sons” — he must be a son at the time of birth.
On the daf / in context: At the moment of birth the child’s sex was indeterminate. Even if later surgery reveals a male, the child was not known as a “ben” at birth and therefore does not share in reducing the bechorah.
Type of Learning
Derash requiring known male status at the moment of birth.
What Is Learned
A tumtum later revealed to be male does not diminish the firstborn’s double portion, because he was not known as a son at birth.