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Author: Omar Metwalli
Helpers assist in raising nondescendent kin, individuals that are not their progeny, by collecting food, building nests, and warding off predators (Canário et al. 2004). Their presence is consequently expected to increase the survival rate of young hatchlings. The helpers, or alloparents, take on a subordinate altruistic role rather than maximizing their own direct reproduction, so as to increase the native parents’ reproductive output. This cost, however, must be outweighed by its benefits if it is to be a positively selected trait.
The benefits of cooperative breeding are more obvious when considered in light of the theory of kin selection formulated by W.D. Hamilton in 1964. Kin selection is a form of natural selection favoring altruistic behavior toward close relatives. Though this behavior does not directly increase an individual’s reproductive fitness, as is possible by personal reproduction, it does provide an evolutionary benefit in the form of indirect reproductive fitness. This idea’s genetic basis is also explained by W.D. Hamilton’s theory, which identifies the ultimate goal of reproduction as the passing on of one’s alleles (Hamilton 1963). Helping to raise nondescendent kin as a helper in cooperative breeding systems achieves this goal, albeit indirectly.
In accordance with his theory, Hamilton developed a rule by which kin selection could be analyzed quantitatively. The rule, which can be written as an inequality, dictates that genes should exhibit increased frequency when rB>C . r represents the genetic relatedness of the recipient to the actor. It is based on the probability a gene picked randomly from each individual will be identical by descent. B stands for the reproductive benefit gained by the recipient, and C denotes the reproductive cost to the altruist. Thus, genes encoding altruistic behavior will gradually become more prevalent if the benefit to the recipient, multiplied by a factor of relatedness, is greater than the cost to the actor. If the cost to the individual performing the action exceeds the product of the beneficiary’s fitness gain and the participants’ genetic relatedness, evolution will select against the gene and its frequency will decrease.
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