In some species, the male bird that helps out the mother bird isn't one of her sons or related to her at all. How can helping a complete stranger make more offspring be selectively advantageous?
In these species, mortality can be quite high. If the breeding male dies while the unrelated male is hanging around being oh-so-helpful, who do you think the female will turn to as a new mate? You've got it: Mr. Helpful himself, who, by assisting her, has given himself the inside track on the job!
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