Kin selection

From the time of antiquity field biologists have observed that some organisms tend to exhibit strategies that favor the reproductive success of their relatives, even at a cost to their own survival and/or reproduction. The classic example is a eusocial insect colony, with sterile females acting as workers to assist their mother in the production of additional offspring. Many evolutionary biologists explain this by the theory of kin selection.
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Natural selection for behaviors that lowers an individual's own chance of survival but raises that of a relative.