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 the fitness of each other. Under natural selection, a gene encoding a trait that enhances the fitness of each individual carrying it should increase in frequency in 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 (i.e. kin selection), may nonetheless increase in frequency, because relatives often carry the same genes. The enhanced fitness of relatives can at times more than compensate for the fitness loss incurred by the individuals displaying the behaviour.
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