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Kin selection

Kin selection was first suggested by Darwin as an explanation to the sterile castes of social insects and has later been mathematically defined by W. D. Hamilton as a mechanism for the evolution of apparently altruistic acts. Under natural selection a gene that causes itself to increase in frequency should become more common in the population. Since identical copies of genes may be carried in relatives, a gene in one organism that prompts behaviour which aids another organism carrying the same gene may become more successful provided that

r × b > c
r = the chance that the aided organism carries the same gene
b = the addition reproductive benefit gained by the recipient of the 'altruistic' act,
c = the reproductive cost to the individual of performing the act.

This leads to the concept that an individual should sacrifice itself in order to save "two siblings, four nephews or eight cousins," since siblings share 50% of an individual's genes, nephews 25% and cousins 12.5% (in a diploid, randomly mating and outbred population).

Kin selection has been used to explain the evolution of humanity's social structure, social insects such as ants and termites, and even the evolution of multicellular animals.

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