Inside its mother’s womb, an unborn sand tiger shark is busy devouring its brothers and sisters. It’s just 10 centimetres long but it already has well-developed eyes and a set of sharp teeth, which it turns against its smaller siblings. By the time the pregnant female gives birth, it only has two babies left—one from each of its two wombs. These survivors have already eaten all the others. They’re the bloody victors of a pre-birth battle.

The arched back, upturned snout and protruding teeth of a sand tiger shark give it a particularly brutish look. Its reproductive habits don’t help. After sex, any fertilised eggs settle in one of the female’s two uteri. Like a quarter of shark species, the