The Kabbalah tells a strange story about the birth of Dinah and Joseph. Leah was fruitful and had given Jacob six sons. She also gave him two more sons through her handmaid, Zilpah. Rachel also gave him two sons through her handmaid, Bilhah. But Rachel herself had long been barren. Now Leah was pregnant again, and at long last so was Rachel. Leah was carrying another boy, and Rachel was carrying a girl.
Leah felt pity and compassion for her sister and prayed to the Lord that Rachel might give birth to the son (so that Rachel would give posterity at least one of the prophesied twelve tribes) and she herself, after having so many sons, would carry the daughter. God heard her prayer and switched the children in their wombs! Leah then gave birth to Dinah, and Rachel gave birth to Joseph.
In Scripture, the birth of a son represents a new spiritual attribute of the Mind, and the birth of a daughter represents a new spiritual attribute of the Heart. Some legends claim that eleven of Jacob’s sons had twin sisters, feminine analogues of the masculine attributes of the brothers (and after hearing of Joseph’s death, Genesis says that all his “sons and daughters” could not comfort him). What this story is really getting at is that the Patriarchs, like Adam when he first was created and like all levels of Divinity, were/are both male and female.
Only Joseph and Dinah were not born with twins. But the miraculous story of their birth shows how deeply they were connected, that they were spiritual twins. Together, these two children represent the male and female aspects of the human Soul.