Editing Kin selection (section)

==Mechanisms==

[[Altruism]] occurs where the instigating individual suffers a fitness loss while the receiving individual experiences a fitness gain. The sacrifice of one individual to help another is an example.<ref>{{cite journal |doi=10.1348/000712606X129213 |last1=Madsen |first1=E. A. |last2=Tunney |first2=R. J. |last3=Fieldman |first3=G. |author4=Plotkin, H. C. |author5=Dunbar, R. I. M. |author6=Richardson, J. M. |author7=McFarland, D. |journal=British Journal of Psychology |volume=98 |issue=2 |pages=339–359 |year=2007 |title=Kinship and Altruism: a Cross-Cultural Experimental Study |pmid=17456276 |url= http://lup.lub.lu.se/search/ws/files/5315300/4091559.pdf |s2cid=18056028}}</ref>

Hamilton outlined two ways in which kin selection altruism could be favoured:

{{Blockquote|The selective advantage which makes behaviour conditional in the right sense on the discrimination of factors which correlate with the relationship of the individual concerned is therefore obvious. It may be, for instance, that in respect of a certain social action performed towards neighbours indiscriminately, an individual is only just breaking even in terms of inclusive fitness. If he could learn to recognise those of his neighbours who really were close relatives and could devote his beneficial actions to them alone an advantage to [[inclusive fitness]] would at once appear. Thus a mutation causing such discriminatory behaviour itself benefits inclusive fitness and would be selected. In fact, the individual may not need to perform any discrimination so sophisticated as we suggest here; a difference in the generosity of his behaviour according to whether the situations evoking it were encountered near to, or far from, his own home might occasion an advantage of a similar kind.<ref name="Hamilton 1964 1–16"/>}}

=== Kin recognition and the green beard effect===

[[File:BeardGreen.jpg|thumb|upright|[[Kin recognition]] theory predicts a selective advantage for the bearers of a trait (like the fictitious [[Green-beard effect|'green beard']]) behave altruistically towards others with the same trait.]]

First, if individuals have the [[kin recognition|capacity to recognise kin]] and to discriminate (positively) on the basis of [[kinship]], then the average relatedness of the recipients of altruism could be high enough for kin selection. Because of the facultative nature of this mechanism, kin recognition and discrimination were expected to be unimportant except among 'higher' forms of life. However, as molecular recognition mechanisms have been shown to operate in organisms such as slime moulds <ref>{{cite journal |doi=10.1038/ncomms8144|last1=Ho |first1=Hsing-I |last2=Shaulsky |first2=Gad | journal=Nature Communications |volume=6  |pages=7144 |year=2015 |title=Temporal regulation of kin recognition maintains recognition-cue diversity and suppresses cheating. |doi-access=free |pmid=26018043 |pmc=4448137 |bibcode=2015NatCo...6.7144H }}</ref> kin recognition has much wider importance than previously recognised. Kin recognition may be selected for inbreeding avoidance, and little evidence indicates that 'innate' kin recognition plays a role in mediating altruism. A thought experiment on the kin recognition/discrimination distinction is the hypothetical [[Green-beard effect|'green beard']], where a gene for social behaviour is imagined also to cause a distinctive phenotype that can be recognised by other carriers of the gene. Due to conflicting genetic similarity in the rest of the genome, there should be selection pressure for green-beard altruistic sacrifices to be suppressed, making common ancestry the most likely form of inclusive fitness.<ref name="Hamilton 1964 1–16"/><ref name=Grafen>{{cite journal |last=Grafen |first=Alan |title=Green beard as death warrant |journal=[[Nature (journal)|Nature]] |volume=394 |pages=521–522 |date=6 August 1998 |url=http://users.ox.ac.uk/~grafen/cv/grbeard.pdf |doi=10.1038/28948 |issue=6693 |s2cid=28124873 |doi-access=free }}</ref> This suppression is overcome if new phenotypes -other beard colours- are  formed through mutation or introduced into the population from time to time. This proposed mechanism goes by the name of 'beard chromodynamics'.<ref>{{cite journal |doi=10.1038/nature04387|last1=Jansen |first1=Vincent A.A. |last2=van Baalen |first2=Minus | journal=Nature |volume=440  |pages=663–666 |year=2006 |title=Altruism through beard chromodynamics. |issue=7084 |pmid=16572169 |bibcode=2006Natur.440..663J |url= https://www.nature.com/articles/nature04387}}</ref>

=== Viscous populations ===

Secondly, indiscriminate altruism may be favoured in "viscous" populations, those with low rates or short ranges of dispersal. Here, social partners are typically related, and so altruism can be selective advantageous without the need for kin recognition and kin discrimination faculties—spatial proximity, together with limited dispersal, ensures that social interactions are more often with related individuals. This suggests a rather general explanation for altruism. Directional selection always favours those with higher rates of [[fecundity]] within a certain population. Social individuals can often enhance the survival of their own kin by participating in and following the rules of their own group.<ref name="Hamilton 1964 1–16"/>

Hamilton later modified his thinking to suggest that an innate ability to recognise actual genetic relatedness was unlikely to be the dominant mediating mechanism for kin altruism:<ref name="H1987">{{cite book |last=Hamilton |first=W. D. |author-link=W. D. Hamilton |date=1987 |chapter=Discriminating Nepotism: Expectable, Common and Overlooked |title=Kin Recognition in Animals |editor1-first=D. J. C. |editor1-last=Fletcher |editor2-first=C. D. |editor2-last=Michener |location=New York |publisher=Wiley |page=425}}</ref>

{{Blockquote|But once again, we do not expect anything describable as an innate kin recognition adaptation, used for social behaviour other than mating, for the reasons already given in the hypothetical case of the trees.}}

Hamilton's later clarifications often go unnoticed. [[Stuart West]] and colleagues have countered the long-standing assumption that kin selection requires innate powers of kin recognition.<ref name="West et al 2011">{{cite journal |last1=West |first1=Stuart A. |author1-link=Stuart West |last2=El Mouden |first2=Claire |last3=Gardner |first3=Andy |year=2011 |title=Sixteen common misconceptions about the evolution of cooperation in humans |journal=Evolution and Social Behaviour |volume=32 |issue=4 |pages=231–262 |citeseerx=10.1.1.188.3318 |doi=10.1016/j.evolhumbehav.2010.08.001|bibcode=2011EHumB..32..231W }}</ref> Another doubtful assumption is that social cooperation must be based on limited dispersal and shared developmental context. Such ideas have obscured the progress made in applying kin selection to species including humans, on the basis of cue-based mediation of [[Social bonding and nurture kinship|social bonding and social behaviours]].<ref>[https://ssrn.com/abstract=1791365 Holland, Maximilian. (2004) ''Social Bonding and Nurture Kinship: Compatibility between Cultural and Biological Approaches''. London School of Economics, PhD Thesis]</ref><ref name="SBNK">Holland, Maximilian. (2012) [[Social Bonding and Nurture Kinship|''Social Bonding and Nurture Kinship: Compatibility between Cultural and Biological Approaches'']]. North Charleston: Createspace Press.</ref>