Editing Kin selection (section)

==Historical overview==

[[File:Charles Darwin by Julia Margaret Cameron, c. 1868.jpg|thumb|upright|[[Charles Darwin]] wrote that selection could be applied to the family as well as to the individual.<ref name="OofS ch8"/>]]

[[Charles Darwin]] was the first to discuss the concept of kin selection (without using that term). In ''On the Origin of Species'', he wrote about the conundrum represented by [[altruistic]] sterile [[social insects]] that:<ref name="OofS ch8">{{cite book |url=http://www.classicreader.com/book/107/59/ |last=Darwin |first=Charles |author-link=Charles Darwin |title=The Origin of Species |pages=Chapter VIII. Instinct: Objections to the theory of natural selection as applied to instincts: neuter and sterile insects |date=1859 |access-date=2013-03-08 |archive-url=https://web.archive.org/web/20160816133513/http://www.classicreader.com/book/107/59/ |archive-date=2016-08-16 |url-status=dead }}</ref>

{{blockquote|This difficulty, though appearing insuperable, is lessened, or, as I believe, disappears, when it is remembered that selection may be applied to the family, as well as to the individual, and may thus gain the desired end. Breeders of cattle wish the flesh and fat to be well marbled together. An animal thus characterised has been slaughtered, but the breeder has gone with confidence to the same stock and has succeeded.|Darwin}}

In this passage "the family" and "stock" stand for a kin group. These passages and others by Darwin about kin selection are highlighted in [[Douglas J. Futuyma|D.J. Futuyma's]] textbook of reference ''Evolutionary Biology''<ref>{{cite book |title=Evolutionary Biology |edition=3 |last=Futuyma |first=Douglas J. |author-link=Douglas J. Futuyma |year=1998 |publisher=Sinauer Associates |location=Sunderland, Massachusetts USA |isbn=978-0-87893-189-7 |page=595}}</ref> and in [[E. O. Wilson]]'s ''[[Sociobiology: The New Synthesis|Sociobiology]]''.<ref>{{cite book |title=Sociobiology: The New Synthesis |edition=25th |last=Wilson |first=Edward O. |author-link=E. O. Wilson |year=2000 |publisher=The Belknap Press of Harvard University Press |location=Cambridge, Massachusetts USA |isbn= 978-0-674-00089-6  |pages=117–118 }}</ref>

Kin selection was briefly referred to by [[R.A. Fisher]] in 1930<ref>{{cite book |title=The Genetical Theory of Natural Selection |last=Fisher |first=R. A. |author-link=R.A. Fisher |year=1930 |publisher=Clarendon Press |location=Oxford |page=[https://archive.org/details/in.ernet.dli.2015.221869/page/n186 159]|url=https://archive.org/details/in.ernet.dli.2015.221869}}</ref> and [[J.B.S. Haldane]] in 1932<ref>{{cite book |title= The Causes of Evolution |last=Haldane |first=J. B. S. |author-link=J.B.S. Haldane |year=1932 |publisher=Longmans, Green & Co |location=London |url=https://archive.org/details/causesofevolutio00hald_0}}</ref> and 1955.<ref>{{cite journal |last=Haldane |first=J. B. S. |author-link=J. B. S. Haldane |year=1955 |title=Population Genetics |journal=New Biology |volume=18 |pages=34–51 }}</ref> J.B.S. Haldane grasped the basic quantities in kin selection, famously writing "I would lay down my life for two brothers or eight [[Cousin chart|cousins]]".<ref name="quote">{{cite book |year=1999 |title=Psychologically Speaking: A Book of Quotations |chapter=Altruism |editor1=Kevin Connolly |editor2=Margaret Martlew |pages=10 |publisher=BPS Books |isbn=978-1-85433-302-5}}</ref> 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 [[inbred|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.<ref>[[q:J. B. S. Haldane]]</ref><ref>{{cite web |url=http://www.brainyquote.com/quotes/quotes/j/johnbsha388700.html |title=John B. S. Haldane Quotes |website=brainyquote.com}}</ref> In 1955 he clarified:<ref>{{cite journal |last=Haldane |first=J. B. S.  |author-link=J.B.S. Haldane |year=1955 |title=Population genetics |journal=New Biology |volume=18 |pages=34–51 }}</ref>

{{blockquote|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<ref>{{cite journal |last=Hamilton |first=W. D. |year=1963 |title=The evolution of altruistic behavior |journal=[[American Naturalist]] |volume=97 |issue= 896|pages=354–356 |doi=10.1086/497114 |bibcode=1963ANat...97..354H |s2cid=84216415 }}</ref> and especially in 1964<ref name="Hamilton 1964 1–16"/><ref name="Hamilton 1964 17–52"/> generalised the concept and developed it mathematically, showing that it holds for genes even when they are not rare, deriving '''Hamilton's rule'''  and defining a new quantity known as an individual's inclusive fitness. He is widely credited as the founder of the field of social evolution. A more elegant mathematical treatment was made possible by [[George R. Price|George Price]] in 1970.<ref>{{Cite journal |last=Price |first=George R. |date=1970-08-01 |title=Selection and Covariance |journal=Nature |language=en |volume=227 |issue=5257 |pages=520–521 |doi=10.1038/227520a0 |pmid=5428476 |bibcode=1970Natur.227..520P |s2cid=4264723 |issn=1476-4687}}</ref>

[[File:John Maynard Smith.jpg|thumb|upright|The evolutionary biologist [[John Maynard Smith]] used the term "kin selection" in 1964.]]

[[John Maynard Smith]] may have coined the actual term "kin selection" in 1964:<ref>{{cite journal |last=Maynard Smith |first=John |author-link=John Maynard Smith |year=1964 |title=Group Selection and Kin Selection |journal=Nature |volume=201 |issue=4924 |pages=1145–1147 |doi=10.1038/2011145a0 |bibcode=1964Natur.201.1145S |s2cid=4177102 }}</ref>

{{blockquote|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 [[sociobiology]]. Some cases of [[evolution]] by [[natural selection]] can only be understood by considering how biological relatives influence each other's [[Fitness (biology)|fitness]]. Under natural selection, a gene encoding a [[Trait (biological)|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]]".<ref>{{cite journal |doi=10.1006/anbe.1996.0019 |last1=Lucas |first1=J. R. |last2=Creel |first2=S. R. |last3=Waser |first3=P. M. |journal=Animal Behaviour |volume=51 |issue=1 |pages=225–228 |year=1996 |title=How to Measure Inclusive Fitness, Revisited|s2cid=53186512 }}</ref> This analysis has been challenged,<ref name=NTW>{{cite journal |last1=Nowak |first1=Martin |author-link=Martin Nowak |author-link3=E.O. Wilson |last2=Tarnita |first2=Corina |last3=Wilson |first3=E. O. |year=2010 |title=The evolution of eusociality |journal=Nature |volume=466 |issue=7310 |pages=1057–1062 |doi=10.1038/nature09205 |pmid=20740005 |pmc=3279739|bibcode=2010Natur.466.1057N }}</ref> Wilson writing that "the foundations of the general theory of inclusive fitness based on the theory of kin selection have crumbled"<ref>{{cite book |last=Wilson |first=E.O. |year=2012 |title=The Social Conquest of Earth |url=https://archive.org/details/socialconquestof0000wils |url-access=registration }}</ref> and that he now relies instead on the theory of [[eusociality]] and "gene-culture co-evolution" for the underlying mechanics of [[sociobiology]]. Inclusive fitness theory is still generally accepted however, as demonstrated by the publication of a rebuttal to Wilson's claims in ''[[Nature (magazine)|Nature]]'' from over a hundred researchers.<ref name="Abbot2011" />

Kin selection is contrasted 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.<ref>{{cite journal |last1=Queller |first1=D. C. |last2=Strassman |first2=J. E. |year=2002 |title=Quick Guide: Kin Selection |journal=[[Current Biology]] |volume=12 |issue=24 |page=R832 |doi=10.1016/s0960-9822(02)01344-1 |pmid=12498698 |s2cid=12698065 |doi-access=free }}</ref><ref>{{cite journal |last1=West |first1=S. A. |last2=Gardner |first2=A. |last3=Griffin |first3=A. S. |year=2006 |title=Quick Guide: Altruism |journal=Current Biology |volume=16 |issue=13 |pages=R482–R483 |doi=10.1016/j.cub.2006.06.014 |pmid=16824903 |doi-access=free }}</ref>