antonlavey
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I keep saying this like people even understand what I'm talking about but I'll keep stressing it. An animal can get its genes successfully into another generation without having children of their own.
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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 the organism's own survival and reproduction. Charles Darwin was the first to discuss the concept of group/kin selection. In the "The Origin of Species", he wrote clearly about altruistic sterile social insects that
In this passage "the family" and "stock" stand for a kin group. These passages and others by Darwin about "kin selection" are highlighted and justly celebrated in D.J. Futuyma's textbook of reference "Evolutionary Biology" [(3rd edit.p595) ] and in E.O Wilson's "Sociobiology" [25th edit.p117-118].
The earliest mathematically formal treatments of kin selection were by R.A. Fisher in 1930 [sup][1][/sup] and J. B. S. Haldane in 1932 [sup][2][/sup] and 1955.[sup][3][/sup] Later on, in works published in 1963[sup][4][/sup] and—most importantly—in 1964,[sup][5][/sup]W. D. Hamilton popularized the concept and the more thorough mathematical treatment given to it by George Price. 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.[sup][6][/sup]
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 hypothetical 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). However the validity of this analysis has recently been challenged.[sup][7][/sup]
[table][tr][td]
[h2]Contents[/h2] [hide]
[/td][/tr][/table][h2][edit] Hamilton's rule[/h2]
- 1 Hamilton's rule
- 2 Mechanisms
- 3 Kin selection and human social patterns
- 4 Examples
- 5 Human examples
- 6 Criticism
- 7 See also
- 8 References
- 9 Further reading
Formally, such genes should increase in frequency when
where
r = the genetic relatedness of the recipient to the actor, often 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.
Originally, the definition for relatedness (r) in Hamilton's rule was explicitly given as Sewall Wright's coefficient of relationship: the probability that at a random locus, the alleles there will be identical by descent (Hamilton 1963, American Naturalist, p. 355). Subsequent authors, including Hamilton, sometimes reformulate this with a regression, which, 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 (Hamilton 1970, Nature & Grafen 1985 Oxford Surveys in Evolutionary Biology). This has been invoked to explain the evolution of spiteful behaviours. Spiteful behavior defines an act (or acts) that results in harm, or loss of fitness, to both the actor and the recipient.
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 would lay down my life for two brothers or eight cousins".[sup][8][/sup]Kin altruism is the term for altruistic behaviour whose evolution is supposed to have been driven by kin selection.
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 a single identical twin of his or more than two full siblings.
In 2011, experimentalists found empirically that Hamilton's rule describes very accurately the conditions under which altruism emerged in simulated populations of foraging robots. The accuracy of this first quantitative corroboration of Hamilton's rule is all the more impressive given that Hamilton's model made several simplifications that did not apply to the foraging robots. [sup][9][/sup]
[h2][edit] Mechanisms[/h2]
An altruistic case is one where the instigating individual suffers a fitness loss while the receiving individual benefits by a fitness gain. The sacrifice of one individual to help another is an example of altruism.
Hamilton (1964) outlined two ways in which kin selection altruism could be favoured.
Kin Recognition: Firstly, if individuals have the capacity to recognize 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 genetic similarity and that this similarity is not necessarily caused by genealogical closeness (kinship).
Viscous Populations: Secondly, even indiscriminate altruism may be favoured in so-called viscous populations, i.e. those characterized 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—spatial proximity serves as a rudimentary form of discrimination. This suggests a rather general explanation for altruism. Directional selection will always favor those with higher rates of fecundity within a certain population. Social individuals can often ensure the survival of their own kin by participating in, and following the rules of a group (assuming the implied faculties for group discrimination).
These mechanisms explain a relatively high r between interacting individuals. Absolute genetic similarity is not a measure of r; rather, r shows the “excess
