Shark Siblingicide

Came across this in a youtube search for something unrelated (I swear distraction is built into the YT search algorithm), but it reminded me of a blog post from back in the day by one of favorite bloggers, Kelsey at From Mauka to Makai, who wrote more generally about sibling rivalry but illustrated this sand tiger example as part of it:

“Sandtiger sharks actually eat their siblings in the womb. Somewhere between four and six months of gestation (around the halfway point) sandtiger embryos grow teeth and develop the ability to swim. Then, the strongest embryo in each uterus (female sandtiger sharks have two) kills and eats its wimpier siblings. With its pesky siblings out of the way, the winning embryo has plenty of room to grow within its very own uterus. And so, after a 9 to 12 month gestation period, the female gives birth to two three-foot long pups. At birth, the pups are a little too big and a little too vicious—they are experienced killers, remember—to tempt predators. That’s a big advantage for the survival of the pups, but a major disadvantage for the survival of the species. Most sharks give birth to at least 12 pups at a time so the sandtiger’s brood of two is rather puny in comparison. And in an ocean of uncertain survival, a puny brood is a one-way ticket to endangered species status.”