In evolutionary biology, 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 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 (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. Evolutionary biology is a subfield of biology concerned with the origin and descent of species, as well as their change, multiplication, and diversity over time. ... For other meanings of this term, see gene (disambiguation). ... Social evolution is a subdiscipline of evolutionary biology that is concerned with social behaviours, i. ... This article is about evolution in biology. ... The Galápagos Islands hold 13 species of finches that are closely related and differ most markedly in the shape of their beaks. ... The Galápagos Islands hold 13 species of finches that are closely related and differ most markedly in the shape of their beaks. ... In biology, a trait or character is a genetically inherited feature of an organism. ... Fitness (often denoted in population genetics models) is a central concept in evolutionary theory. ...

Hamilton's rule

Formally, such genes should increase in frequency when

rB − C > 0

where

r = the genetical relatedness of the recipient to the actor, usually defined as the probability that a gene picked randomly from each at the same locus is identical by descent.

B = the additional reproductive benefit gained by the recipient of the altruistic act,

C = the reproductive cost to the individual of performing the act.

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. The phrase Kin selection, however, was coined by John Maynard Smith. Short and long arms Chromosome. ... W. D. Hamilton William Donald Bill Hamilton, F.R.S. (1 August 1936 — 7 March 2000) was a British evolutionary biologist, considered one of the greatest evolutionary theorists of the 20th century. ... This article is about evolution in biology. ... Professor John Maynard Smith[1], F.R.S. (6 January 1920 – 19 April 2004) was a British evolutionary biologist and geneticist. ...

Technically, the correct definition for relatedness (r) in Hamilton's rule describes it as a regression measure. Regressions, unlike probabilities, can be negative, and so it is possible for individuals to be negatively related, which simply means that two individuals can be less genetically alike than two random ones on average. This has been invoked to explain the evolution of spiteful behaviours. In statistics regression toward the mean, sometimes called the regression effect in other disciplines, is a principle stating a relationship between a measurement that is used to split a population into groups, and a second measurement of the groups thereby created. ... In fair division problems, spite is a phenomenon that occurs when a players value of an allocation decreases when one or more other players valuation increases. ...

In the 1930s J.B.S. Haldane had full grasp of the basic quantities and considerations that play a role in kin selection. He famously said that, "I'd lay down my life for two brothers or eight cousins".^[1] Kin altruism is the term for altruistic behaviour whose evolution is supposed to have been driven by kin selection. John Burdon Sanderson Haldane (November 5, 1892 - December 1, 1964), who normally used J.B.S. as a first name, was a geneticist born in Scotland and educated at Eton and Oxford University. ... This article or section does not cite its references or sources. ...

Haldane's remark alluded to the fact that if an individual loses its life to save two siblings, four nephews, or eight cousins, it is a "fair deal" in evolutionary terms, as siblings are on average 50% identical by descent, nephews 25%, and cousins 12.5% (in a diploid population that is randomly mating and previously outbred). But Haldane also joked that he would truly die only to save more than one identical set of twins or more than two full siblings. Diploid (meaning double in Greek) cells have two copies (homologs) of each chromosome (both sex- and non-sex determining chromosomes), usually one from the mother and one from the father. ... Inbreeding is breeding between close relatives. ...

Mechanisms

Hamilton (1964) outlined two ways in which kin selected altruism could be favoured. This article or section may contain original research or unverified claims. ...

Firstly, if individuals have the capacity to recognise kin (kin recognition) and to adjust their behaviour on the basis of kinship (kin discrimination), then the average relatedness of the recipients of altruism could be high enough for this to be favoured. Because of the facultative nature of this mechanism, it is generally regarded that kin recognition and discrimination are unimportant except among 'higher' forms of life (although there is some evidence for this mechanism among protozoa). A special case of the kin recognition/discrimination mechanism is the hypothetical 'green beard', where a gene for social behaviour also causes a distinctive phenotype that can be recognised by other carriers of the gene. Hamilton's discussion of greenbeard altruism serves as an illustration that relatedness is a matter of genetical similarity and that this similarity is not necessarily caused by genealogical closeness (kinship). The selfish gene theory postulates that natural selection will increase the frequency of those genes whose phenotypic effects ensure their successful replication. ...

Secondly, even indiscriminite altruism may be favoured in so-called viscous populations, i.e. those characterised by low rates or short ranges of dispersal. Here, social partners are typically genealogically-close kin, and so altruism may be able to flourish even in the absence of kin recognition and kin discrimination faculties. This suggests a rather general explanation for altruism.

Social insects are an excellent example of organisms that display kin selected traits. The workers of some species are sterile, a trait that would not occur if individual selection was the only process at work. The relatedness coefficent r is very high between the worker hymenoptera due to haplodiploidy, and Hamilton's rule is satisfied because the benefits in fitness for the queen are reflected in indirect fitness for the individual workers, and the increased efficiency provided by group living means that the costs are far outweighed by the benefits. Suborders Apocrita Symphyta Many families, see article Hymenoptera is one of the larger orders of Insects, comprising the sawflies, wasps, bees, and ants. ... The Haplodiploid sex-determination system is a system that some Hymenopterans (bees, ants, and wasps), and coleopterans (bark beetles) use to determine the sex of their offspring, and preserve eusociality. ... Fitness (often denoted in population genetics models) is a central concept in evolutionary theory. ...

See also

• Group selection
• Inclusive fitness
• Selfish gene

In evolutionary biology, group selection refers to the idea that alleles can become fixed or spread in a population because of the benefits they bestow on groups, regardless of the fitness of individuals within that group. ... Inclusive fitness encompasses conventional Darwinian fitness with the addition of behaviors that contribute to an organism’s individual fitness through altruism. ... The Selfish Gene is a controversial book by Richard Dawkins published in 1976. ...

References

1. ^ (1999) "Altruism", in Kevin Connolly and Maragaret Martlew: Psychologically Speaking: A Book of Quotations. BPS Books, 10. ISBN 1-85433-302-X.  (see also: Haldane's Wikiquote entry)

• Hamilton, W.D. (1964). The genetical evolution of social behaviour I and II. — Journal of Theoretical Biology 7: 1-16 and 17-52. pubmed I pubmed II
• Lucas, J.R., Creel, S.R. & Waser, P.M. (1996) How to measure inclusive fitness, revisited, Animal Behaviour, 51, 225-228.
• Madsen, E.A., Tunney, R., Fieldman, G., Plotkin, H.C., Dunbar, R.I.M., Richardson, J.M., & McFarland, D. (in press) Kinship and altruism: A cross-cultural experimental study. British Journal of Psychology [1]
• Queller, D.C. & Strassman, J.E. (2002) Quick Guide: Kin Selection. Current Biology,12,R832. [2]
• West, S.A., Gardner, A. & Griffin, A.S. (2006) Quick Guide: Altruism. Current Biology,16,R482-R483. [3]