As soon as tiger shark embryos develop teeth, they attack and eat each other in utero. Up to 12 babies start out, while usually only two make it out alive, all but one being eaten by the largest baby in the litter. As a result, tiger shark babies are generally much larger than babies of other shark species, so they’re relatively safe from predators.
Paternal DNA may also play a role. At any given time, pregnant sharks can have two to three different DNAs in their embryos—meaning 2-3 different fathers—and scientists have hypothesized that the male sharks attack and eat the other ones that are not of the same genetic makeup as they are.