Editing Kin selection (section)

==In humans==
{{Main|Inclusive fitness in humans}}

Whether or not [[Hamilton's rule]] always applies, relatedness is often important for human altruism, in that humans are inclined to behave more altruistically toward kin than toward unrelated individuals.<ref name=Cartwright>Cartwright, J. (2000). ''Evolution and human behavior: Darwinian perspectives on human nature.'' Massachusetts: MIT Press.</ref>  Many people choose to live near relatives, exchange sizeable gifts with relatives, and favour relatives in wills in proportion to their relatedness.<ref name=Cartwright/>

===Experimental studies, interviews, and surveys===<!--should be recast to emphasize findings, not research studies-->
Interviews of several hundred women in Los Angeles showed that while non-kin friends were willing to help one another, their assistance was far more likely to be reciprocal.  The largest amounts of non-reciprocal help, however, were reportedly provided by kin.  Additionally, more closely related kin were considered more likely sources of assistance than distant kin.<ref>{{cite journal |last1=Essock-Vitale |first1=S. M. |last2=McGuire |first2=M. T. |year=1985 |title=Women's lives viewed from an evolutionary perspective. II. Patterns in helping |journal=Ethology and Sociobiology |volume=6 |issue=3 |pages=155–173 |doi=10.1016/0162-3095(85)90028-7 }}</ref> Similarly, several surveys of American college students found that individuals were more likely to incur the cost of assisting kin when a high probability that relatedness and benefit would be greater than cost existed.  Participants' feelings of helpfulness were stronger toward family members than non-kin.  Additionally, participants were found to be most willing to help those individuals most closely related to them.  Interpersonal relationships between kin in general were more supportive and less Machiavellian than those between non-kin.<ref>{{cite journal |last=Barber |first=N. |year=1994 |title=Machiavellianism and altruism: Effects of relatedness of target person on Machiavellian and helping attitudes |journal=Psychological Reports |volume=75 |pages=403–22 |doi=10.2466/pr0.1994.75.1.403 |s2cid=144789875 }}</ref>

In one experiment, the longer participants (from both the UK and the South African Zulus) held a painful skiing position, the more money or food was presented to a given relative. Participants repeated the experiment for individuals of different relatedness (parents and siblings at r=.5, grandparents, nieces, and nephews at r=.25, etc.). The results showed that participants held the position for longer intervals the greater the degree of relatedness between themselves and those receiving the reward.<ref>{{cite journal |last1=Madsen |first1=E. A. |year=2007 |url= http://portal.research.lu.se/ws/files/5315300/4091559.pdf |title=Kinship and altruism: A cross-cultural experimental study |journal=British Journal of Psychology |volume=98 |issue=Pt 2 |pages=339–359 |doi=10.1348/000712606X129213 |pmid=17456276 |last2=Tunney |first2=R. J. |last3=Fieldman |first3=G. |display-authors=3 |last4=Plotkin |first4=Henry C. |last5=Dunbar |first5=Robin I. M. |last6=Richardson |first6=Jean-Marie |last7=McFarland |first7=David |s2cid=18056028}}</ref>

===Observational studies===
A study of food-sharing practices on the West Caroline islets of [[Ifalik|Ifaluk]] determined that food-sharing was more common among people from the same islet, possibly because the degree of relatedness between inhabitants of the same islet would be higher than relatedness between inhabitants of different islets.  When food was shared between islets, the distance the sharer was required to travel correlated with the relatedness of the recipient—a greater distance meant that the recipient needed to be a closer relative.  The relatedness of the individual and the potential inclusive fitness benefit needed to outweigh the energy cost of transporting the food over distance.<ref>{{cite journal |last1=Betzig |first1=L. |last2=Turke |first2=P. |year=1986 |title=Food sharing on Ifaluk |journal=Current Anthropology |volume=27 |issue=4 |pages=397–400 |doi=10.1086/203457 |s2cid=144688339 }}</ref>

Humans may use the inheritance of material goods and wealth to maximise their inclusive fitness.  By providing close kin with inherited wealth, an individual may improve his or her kin's reproductive opportunities and thus increase his or her own inclusive fitness even after death.  A study of a thousand wills found that the beneficiaries who received the most inheritance were generally those most closely related to the will's writer.  Distant kin received proportionally less inheritance, with the least amount of inheritance going to non-kin.<ref>{{cite journal |last1=Smith |first1=M. |first2=B. |first3=C. |year=1987 |title=Inheritance of wealth as human kin investment |journal=Ethology and Sociobiology |volume=8 |issue=3|pages=171–182 |doi=10.1016/0162-3095(87)90042-2 |last2=Kish |last3=Crawford }}</ref>

A study of childcare practices among Canadian women found that respondents with children provide childcare reciprocally with non-kin.  The cost of caring for non-kin was balanced by the benefit a woman received—having her own offspring cared for in return.  However, respondents without children were significantly more likely to offer childcare to kin.  For individuals without their own offspring, the inclusive fitness benefits of providing care to closely related children might outweigh the time and energy costs of childcare.<ref>{{cite journal |last1=Davis |first1=J. N. |first2=M. |year=1997 |title=Evolutionary theory and the human family |journal=Quarterly Review of Biology |volume=72 |issue=4|pages=407–35 |doi=10.1086/419953 |pmid=9407672 |last2=Daly |s2cid=25615336 }}</ref>

Family investment in offspring among black South African households also appears consistent with an inclusive fitness model. A higher degree of relatedness between children and their caregivers was correlated with a higher degree of investment in the children, with more food, health care, and clothing. Relatedness was also associated with the regularity of a child's visits to local medical practitioners and with the highest grade the child had completed in school, and negatively associated with children being behind in school for their age.<ref>{{cite journal |last=Anderson |first=K. G. |year=2005 |title=Relatedness and investment: Children in South Africa |journal=Human Nature |volume=16 |issue=1|pages=1–31 |doi=10.1007/s12110-005-1005-4 |pmid=26189514 |s2cid=23623318 }}</ref>

Observation of the [[Dolgans|Dolgan]] hunter-gatherers of northern Russia suggested that there are larger and more frequent asymmetrical transfers of food to kin. Kin are more likely to be welcomed to non-reciprocal meals, while non-kin are discouraged from attending.  Finally, when reciprocal food-sharing occurs between families, these families are often closely related, and the primary beneficiaries are the offspring.<ref>{{cite journal |last1=Ziker |first1=J. |last2=Schnegg |first2=M. |year=2005 |title=Food sharing at meals: Kinship, reciprocity, and clustering in the Taimyr Autonomous Okrug, northern Russia |journal=Human Nature |volume=16 |issue=2 |pages=178–210 |doi=10.1007/s12110-005-1003-6 |pmid=26189622 |s2cid=40299498 }}</ref>

Violence in families is more likely when step-parents are present, and that "genetic relationship is associated with a softening of conflict, and people's evident valuations of themselves and of others are systematically related to the parties' reproductive values".<ref>{{cite journal |last1=Daly |last2=Wilson |first1=M. |year=1988 |title=Evolutionary social-psychology and family homicide |journal=Science |volume=242 |issue=4878 |pages=519–524 |doi=10.1126/science.3175672 |pmid=3175672 |bibcode=1988Sci...242..519D }}</ref> Numerous studies suggest how inclusive fitness may work amongst different peoples, such as the Ye'kwana of southern Venezuela, the Gypsies of Hungary, and the doomed Donner Party of the United States.<ref>{{cite journal |last=Hames |first=R. |year=1979 |title=Garden labor exchange among the Ye'kwana |journal=Ethology and Sociobiology |volume=8 |issue=4|pages=259–84 |doi=10.1016/0162-3095(87)90028-8 }}</ref><ref>{{cite journal |last=Bereczkei |first=T. |year=1998 |title=Kinship network, direct childcare, and fertility among Hungarians and Gypsies |journal=Evolution and Human Behavior |volume=19 |issue=5|pages=283–298 |doi=10.1016/S1090-5138(98)00027-0 |bibcode=1998EHumB..19..283B }}</ref><ref>{{cite journal |last=Grayson |first=D. K. |year=1993 |title=Differential mortality and the Donner Party disaster |journal=Evolutionary Anthropology |volume=2 |issue=5|pages=151–9 |doi=10.1002/evan.1360020502 |s2cid=84880972 }}</ref><ref>{{cite book |last=Dunbar |first=R. |year=2008 |chapter=Kinship in biological perspective |editor1=N. J. Allen |editor2=H. Callan |editor3=R. Dunbar |editor4=W. James |title=Early human kinship: From sex to social reproduction |pages=131–150 |location=New Jersey |publisher=Blackwell Publishing}}</ref>

===Human social patterns===

[[File:Coloured-family.jpg|thumb|[[Family|Families]] are important in human behaviour, but kin selection may be based on closeness and other cues.]]
{{See also|Human inclusive fitness|Nurture kinship}}

[[Evolutionary psychology|Evolutionary psychologists]], following [[Darwinian anthropology|early human sociobiologists']] interpretation<ref name="D&W1999">{{cite book |last1=Daly |first1=M. |last2=Wilson |first2=M. I. |date=1999 |chapter=An evolutionary psychological perspective on homicide |title=Homicide Studies: A Sourcebook of Social Research |editor1-last=Smith |editor1-first=D. |editor2-last=Zahn |editor2-first=M. |location=Thousand Oaks |publisher=Sage Publications}}</ref> of kin selection theory initially attempted to explain human altruistic behaviour through kin selection by stating that "behaviors that help a genetic relative are favored by natural selection." However, many evolutionary psychologists recognise that this common shorthand formulation is inaccurate:<ref name="P2007">{{cite journal |last1=Park |first1=J.H. |year=2007 |title=Persistent Misunderstandings of Inclusive Fitness and Kin Selection: Their Ubiquitous Appearance in Social Psychology Textbooks |journal=Evolutionary Psychology |volume=5 |issue=4|pages=860–873 |doi=10.1177/147470490700500414 |doi-access=free }}</ref>

{{blockquote|Many misunderstandings persist.  In many cases, they result from conflating "coefficient of relatedness" and "proportion of shared genes", which is a short step from the intuitively appealing—but incorrect—interpretation that "animals tend to be altruistic toward those with whom they share a lot of genes." These misunderstandings don't just crop up occasionally; they are repeated in many writings, including undergraduate psychology textbooks—most of them in the field of social psychology, within sections describing evolutionary approaches to altruism.}}

As with the earlier sociobiological forays into the cross-cultural data, typical approaches are not able to find explanatory fit with the findings of ethnographers insofar that human kinship patterns are not necessarily built upon blood-ties. However, as Hamilton's later refinements of his theory make clear, it does not simply predict that genetically related individuals will inevitably recognise and engage in positive social behaviours with genetic relatives: rather, indirect context-based mechanisms may have evolved, which in historical environments have met the inclusive fitness criterion. Consideration of the demographics of the typical evolutionary environment of any species is crucial to understanding the evolution of social behaviours. As Hamilton himself put it, "Altruistic or selfish acts are only possible when a suitable social object is available. In this sense behaviours are conditional from the start".<ref name="H1987"/>

Under this perspective, and noting the necessity of a reliable context of interaction being available, the data on how altruism is mediated in social mammals is readily made sense of. In social mammals, primates and humans, altruistic acts that meet the kin selection criterion are typically mediated by circumstantial cues such as shared developmental environment, familiarity and social bonding.<ref name="S1997">Sherman et al (1997) ''Recognition Systems''. In ''Behavioural Ecology'', edited by J. R. Krebs and N. B. Davies. Oxford: Blackwell Scientific.</ref> That is, it is the context that mediates the development of the bonding process and the expression of the altruistic behaviours, not genetic relatedness as such. This interpretation is compatible with the cross-cultural ethnographic data and has been called [[nurture kinship]].<ref name="SBNK"/>