I remind you, as always:
After mating, a female produces as many as 40 fertilized embryos, separated between two separate wombs. The embryos take nearly a year to fully develop, but they begin hunting long before that. After about two months, their own yolk sacs go dry. Hungry, they start eating their brothers and sisters. After the rampant in utero cannibalization, only one shark -- the biggest and strongest -- is left in each womb.