When Does It Make Sense To Kill Your Sibling?

When a baby sand tiger shark hatches from its egg, it finds itself trapped inside its mom's uterus, forced to eat its siblings or to be eaten. It's super weird, but pitting your kids against each other can actually sometimes be a winning parental strategy. Hi, I'm Cameron and this is Minute Earth. Is that copyrighted? It's common for siblings to fight for food, for attention, or to establish dominance. And in many cases, parents step in to make sure the rivalry doesn't go too far. Not just out of, you know, love and whatnot, but because the more babies you have, the more genes you get to pass on. In some species, though, parents actually promote a fight to the death. Take black eagles for example. A black eagle pair will always lay two eggs per nest, despite the fact that there's never enough food around to actually feed two hungry eagle chicks. This scenario forces the chicks to fight for survival. It is brutal, but let's think about it for a second. If the parents had just laid one egg, they'd still need to spend the same amount of time and energy building the nest, defending it from intruders and predators, and incubating the egg. But sometimes that one egg might not hatch, or the resulting chick might get sick and die. In those cases, all that work is for nothing. So, as long as the parents have to go to all of that trouble, it makes sense to lay two eggs so that one can serve as a backup. If both eggs are healthy, the parents only have to take care of the stronger, healthier one that emerges victorious from the thundome. And black eagles aren't alone in this. Some other birds and insect species also bear extra offspring as an insurance policy, only to pit the survivors against each other. But the sand tiger shark takes sibling rivalry to an extreme. A mama shark can incubate as many as 20 eggs at a time in her uterus. So theoretically, she could birth 20 babies at once. But all of those babies would be way too small to thrive. They couldn't hunt or escape predators. So instead, female sand tiger sharks have evolved reproductive systems that trap their babies inside after hatching, forcing them to snack on their own siblings in order to survive. And after several months, the sole survivor is born. It's now a meter long with a full mouth of razor teeth and ready to take on the open ocean. In contrast to such brutal beginnings, isn't it nice that our human parents mostly just want us to get along? This video is brought to you by you. That's because you guys have been buying our awesome new animal taxonomy posters by the buttload, which I found out recently is actually a technical term. Old English beer casks were called butts. So, a buttload means something like 500 L, which equals roughly a thousand poster tubes. Our most popular poster isn't about butts, though. It's about the dog family, and it shows how all of them, from foxes to wolves to coyotes to Chihuahua, are all related, and they're each beautifully drawn by our awesome team of illustrators. To get your own, head over to dftba. com/minuteearth. That's dftba. com/mminar. Thanks a buttload.