|
Kin selection is the evolutionary strategy that favours the reproductive success of an organism's relatives, even at a cost to the organism's own survival and reproduction. Kin altruism is altruistic behaviour whose evolution is driven by kin selection. Kin selection is an instance of inclusive fitness, which combines the number of offspring produced with the number an individual can produce by supporting others, such as siblings. Charles Darwin discussed the concept of kin selection in his 1859 book, ''The Origin of Species'', where he reflected on the puzzle of sterile social insects, such as honey bees, which leave reproduction to their sisters, arguing that a selection benefit to related organisms (the same "stock") would allow the evolution of a trait that confers the benefit but destroys an individual at the same time. R.A. Fisher in 1930 and J.B.S. Haldane in 1932 set out the mathematics of kin selection, with Haldane famously joking that he would willingly die for two brothers or eight cousins.〔Wikiquote:J. B. S. Haldane〕〔http://www.brainyquote.com/quotes/quotes/j/johnbsha388700.html〕 In 1964, W.D. Hamilton popularised the concept and the major advance in the mathematical treatment of the phenomenon by George R. Price which has become known as "Hamilton's rule". In the same year John Maynard Smith used the actual term kin selection for the first time. According to Hamilton's rule, kin selection causes genes to increase in frequency when the genetic relatedness of a recipient to an actor multiplied by the benefit to the recipient is greater than the reproductive cost to the actor. The rule is difficult to test but a study of red squirrels in 2010 found that adoption of orphans by surrogate mothers in the wild occurred only when the conditions of Hamilton's rule were met. Hamilton proposed two mechanisms for kin selection: kin recognition, where individuals are able to identify their relatives, and viscous populations, where dispersal is rare enough for populations to be closely related. The viscous population mechanism makes kin selection and social cooperation possible in the absence of kin recognition. Nurture kinship, the treatment of individuals as kin when they live together, is sufficient for kin selection, given reasonable assumptions about dispersal rates. Kin selection is not the same thing as group selection, where natural selection acts on the group as a whole. In humans, altruism is more likely and on a larger scale with kin than with unrelated individuals; for example, humans give presents according to how closely related they are to the recipient. In other species, vervet monkeys use allomothering, where related females such as older sisters or grandmothers often care for young, according to their relatedness. The social shrimp ''Synalpheus regalis'' protects juveniles within highly related colonies. ==Historical overview== Charles Darwin was the first to discuss the concept of kin selection. In ''The Origin of Species'', he wrote clearly about the conundrum represented by 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 in D.J. Futuyma's textbook of reference ''Evolutionary Biology'' and in E. O. Wilson's ''Sociobiology''. The earliest mathematically formal treatments of kin selection were by R.A. Fisher in 1930 and J.B.S. Haldane in 1932 and 1955. J.B.S. Haldane fully grasped the basic quantities and considerations in kin selection, famously writing "I would lay down my life for two brothers or eight cousins".〔 (see also: Haldane's Wikiquote entry)〕 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 1955 he clarified: Let us suppose that you carry a rare gene that affects your behaviour so that you jump into a flooded river and save a child, but you have one chance in ten of being drowned, while I do not possess the gene, and stand on the bank and watch the child drown. If the child's your own child or your brother or sister, there is an even chance that this child will also have this gene, so five genes will be saved in children for one lost in an adult. If you save a grandchild or a nephew, the advantage is only two and a half to one. If you only save a first cousin, the effect is very slight. If you try to save your first cousin once removed the population is more likely to lose this valuable gene than to gain it. … It is clear that genes making for conduct of this kind would only have a chance of spreading in rather small populations when most of the children were fairly near relatives of the man who risked his life. W. D. Hamilton, in 1963 and especially in 1964, popularised the concept and the more thorough mathematical treatment given to it by George Price. John Maynard Smith may have coined the actual term "kin selection" in 1964: 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. Kin selection causes changes in gene frequency across generations, driven by interactions between related individuals. This dynamic forms the conceptual basis of the theory of social evolution. Some cases of evolution by natural selection can only be understood by considering how biological relatives influence each other'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 behaviour, may nonetheless increase in frequency, because relatives often carry the same gene. According to this principle, the enhanced fitness of relatives can at times more than compensate for the fitness loss incurred by the individuals displaying the behaviour, making kin selection possible. This is a special case of a more general model, "inclusive fitness". This analysis has been challenged, Wilson writing that "the foundations of the general theory of inclusive fitness based on the theory of kin selection have crumbled" and that he now relies instead on the theory of eusociality and "gene-culture co-evolution" for the underlying mechanics of sociobiology. "Kin selection" should not be confused with "group selection" according to which a genetic trait can become prevalent within a group because it benefits the group as a whole, regardless of any benefit to individual organisms. All known forms of group selection conform to the principle that an individual behaviour can be evolutionarily successful only if the genes responsible for this behaviour conform to Hamilton's Rule, and hence, on balance and in the aggregate, benefit from the behaviour. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Kin selection」の詳細全文を読む スポンサード リンク
|