When Does It Make Sense To Kill Your Sibling?

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0:00When a baby sand tiger shark hatches

0:02from its egg, it finds itself trapped

0:04inside its mom's uterus, [music] forced

0:06to eat its siblings or to be eaten. It's

0:09super weird, but pitting your kids

0:11against each other [music] can actually

0:13sometimes be a winning parental

0:15strategy. Hi, I'm Cameron and this is

0:18Minute Earth.

0:20Minute Earth. Is that copyrighted? It's

0:23common for siblings to fight for food,

0:25for attention, or to establish

0:27dominance. And in many cases, parents

0:30step in to make sure the rivalry doesn't

0:32go too far. Not just out of, you know,

0:34love and whatnot, but because the more

0:36babies you have, the more genes you get

0:38to pass on. In some species, though,

0:40parents actually promote a fight to the

0:43death. Take black [music] eagles for

0:45example. A black eagle pair will always

0:47lay two eggs per nest, despite the

0:49[music] fact that there's never enough

0:51food around to actually feed two hungry

0:53eagle chicks. This scenario forces the

0:55chicks to fight for survival. It is

0:58brutal, but [music] let's think about it

0:59for a second. If the parents had just

1:01laid one egg, they'd still need to spend

1:04the same amount of time and energy

1:05building the nest, defending it from

1:07intruders and predators, and incubating

1:09the egg. But sometimes that one egg

1:12might not hatch, or the resulting chick

1:14might get sick and die. In those cases,

1:16all that work is for nothing. So, as

1:18long as the parents have to go to all of

1:20that trouble, it makes sense to lay two

1:22eggs so that one can serve as a backup.

1:24If both eggs are healthy, the parents

1:26only have to take care of the stronger,

1:28healthier one that emerges victorious

1:30[music]

1:30from the thundome. And black eagles

1:33aren't alone in this. Some other birds

1:35and insect species also bear extra

1:37offspring as an insurance policy, only

1:39to pit the survivors against each other.

1:41But the sand tiger shark takes sibling

1:44rivalry to an extreme. A mama [music]

1:46shark can incubate as many as 20 eggs at

1:49a time in her uterus. So theoretically,

1:51she could birth 20 babies at once. But

1:53all of those babies would be way too

1:55small to thrive. They couldn't hunt or

1:57escape predators. So instead, female

1:59sand tiger sharks have evolved

2:00reproductive systems that trap their

2:02babies inside after hatching, forcing

2:04them to snack on their own siblings in

2:06order to survive. And after several

2:08months, the sole survivor is born. It's

2:10now a meter long with a full mouth of

2:12razor teeth and ready to take on the

2:14open ocean. In contrast to such brutal

2:17beginnings, isn't it nice that our human

2:20parents mostly just want us to get

2:22along?

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When Does It Make Sense To Kill Your Sibling?

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