A female sand tiger shark has two wombs, though can have multiple fetuses in each. However, only one from each womb will survive to birth. That’s because survival of the fittest is already in play inside the mother shark.
Female sand tiger sharks often mate with more than one male, which means that she could have young that are fathered by two different males. This is a way for the mother to be sure that when she gives birth to her young, they are the strongest she could hope for.
Sand tiger shark fetuses are so voracious they have been known to bite scientists while they are probing a pregnant females uterus. At only 10 cm long, they are already living out their vicious reputation. Natural selection at its most basic. Let the babies fight it out.
Source: National Geographic