Kin selection

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Kin selection refers to apparent strategies in evolution that favor the reproductive success of an organism's relatives, even at a cost to their own survival and/or reproduction. The classic example is a eusocial insect colony, in which sterile females act as workers to assist their mother in the production of additional offspring.

The earliest expressions of the basic concepts were by R.A. Fisher in 1930,[1] J. B. S. Haldane in 1955,[2] but it was W. D. Hamilton who truly formalized the concept, in works published in 1963[3] and—most importantly—in 1964.[4] The term "kin selection" may first have been coined by John Maynard Smith in 1964 when he wrote:

These processes I will call kin selection and group selection respectively. Kin selection has been discussed by Haldane and by Hamilton. … By kin selection I mean the evolution of characteristics which favour the survival of close relatives of the affected individual, by processes which do not require any discontinuities in the population breeding structure.[5]

Kin selection refers to changes in gene frequency across generations that are driven at least in part by interactions between related individuals, and this forms much of the conceptual basis of the theory of social evolution. Indeed, some cases of evolution by natural selection can only be understood by considering how biological relatives influence one another's fitness. Under natural selection, a gene encoding a trait that enhances the fitness of each individual carrying it should increase in frequency within the population; and conversely, a gene that lowers the individual fitness of its carriers should be eliminated. However, a gene that prompts behaviour which enhances the fitness of relatives but lowers that of the individual displaying the behavior, may nonetheless increase in frequency, because relatives often carry the same gene; this is the fundamental principle behind the theory of kin selection. According to the theory, the enhanced fitness of relatives can at times more than compensate for the fitness loss incurred by the individuals displaying the behaviour. As such, this is a special case of a more general model, called inclusive fitness (in that inclusive fitness refers simply to gene copies in other individuals, without requiring that they be kin).


Hamilton's rule

Formally, such genes should increase in frequency when


This inequality is known as Hamilton's rule after W. D. Hamilton who published, in 1964, the first formal quantitative treatment of kin selection to deal with the evolution of apparently altruistic acts. Altruistic acts are those that benefit the recipient but harm the actor. The phrase Kin selection, however, was coined by John Maynard Smith.

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