Mountain bluebirds: experimental evidence against altruism.
The frequency of true altruism in nature requires assessment because, if true altruism is common, Darwin's theory of natural selection is inadequate to account for all of evolution. An experiment provided birds with the opportunity to behave truly altruistically. One member of each of 25 wild pairs was collected. Ten of these were replaced naturally by courting birds, or consorts. Only one consort fostered the young of her prospective mate, and her behavior was interpretable as a reproductive error. Other consorts behaved reproductively selfishly.
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