When Does It Make Sense To Kill Your Sibling?

TL;DR

Killing siblings is a winning survival strategy when parents can't feed all offspring and need a backup egg as insurance.

Key Points

• 1.Black eagles always lay 2 eggs despite only having food for one chick — the second egg is a biological insurance policy in case the first egg fails to hatch or the chick dies.
• 2.Sand tiger sharks incubate up to 20 eggs in the uterus, but trap the hatchlings inside, forcing them to cannibalize siblings for months until one meter-long survivor is born with a full set of teeth.
• 3.The evolutionary logic: the extra effort of raising one backup offspring is minimal compared to the risk of total reproductive failure if only one egg is laid.