Editing Evolutionary psychology (section)

===Family and kin===
{{see also|Human inclusive fitness|Kin selection}}
Inclusive fitness is the sum of an organism's classical fitness (how many of its own offspring it produces and supports) and the number of equivalents of its own offspring it can add to the population by supporting others.<ref>{{cite web|url=http://www.personalityresearch.org/evolutionary/inclusive.html|title=Evolutionary Psychology – Inclusive Fitness|access-date=10 August 2016}}</ref> The first component is called classical fitness by Hamilton (1964).

From the gene's point of view, evolutionary success ultimately depends on leaving behind the maximum number of copies of itself in the population. Until 1964, it was generally believed that genes only achieved this by causing the individual to leave the maximum number of viable offspring. However, in 1964 W. D. Hamilton proved mathematically that, because close relatives of an organism share some identical genes, a gene can also increase its evolutionary success by promoting the reproduction and survival of these related or otherwise similar individuals. Hamilton concluded that this leads natural selection to favor organisms that would behave in ways that maximize their inclusive fitness. It is also true that natural selection favors behavior that maximizes personal fitness.

Hamilton's rule describes mathematically whether or not a gene for altruistic behavior will spread in a population:
:<math>rb > c \ </math>
where
* <math>c \ </math> is the reproductive cost to the altruist,
* <math>b \ </math> is the reproductive benefit to the recipient of the altruistic behavior, and
* <math>r \ </math> is the probability, above the population average, of the individuals sharing an altruistic gene – commonly viewed as "degree of relatedness".

The concept serves to explain how natural selection can perpetuate altruism. If there is an "altruism gene" (or complex of genes) that influences an organism's behavior to be helpful and protective of relatives and their offspring, this behavior also increases the proportion of the altruism gene in the population, because relatives are likely to share genes with the altruist due to [[identical by descent|common descent]]. Altruists may also have some way to recognize altruistic behavior in unrelated individuals and be inclined to support them. As Dawkins points out in ''The Selfish Gene'' (Chapter 6) and ''The Extended Phenotype'',<ref>Dawkins, Richard, "The Extended Phenotype", Oxford University Press 1982 (Chapter 9)</ref> this must be distinguished from the [[green-beard effect]].

Although it is generally true that humans tend to be more altruistic toward their kin than toward non-kin, the relevant proximate mechanisms that mediate this cooperation have been debated (see [[kin recognition]]), with some arguing that kin status is determined primarily via social and cultural factors (such as co-residence, maternal association of sibs, etc.),<ref name=W2010>{{cite journal |doi=10.1016/j.evolhumbehav.2010.08.001 |title=Sixteen common misconceptions about the evolution of cooperation in humans |year=2011 |last1=West |first1=Stuart A. |last2=El Mouden |first2=Claire |last3=Gardner |first3=Andy |journal=Evolution and Human Behavior |volume=32 |issue=4 |pages=231–62 |bibcode=2011EHumB..32..231W |url=http://www.zoo.ox.ac.uk/group/west/pdf/WestElMoudenGardner_11.pdf |access-date=25 October 2017 |archive-url=https://web.archive.org/web/20170812085608/http://www.zoo.ox.ac.uk/group/west/pdf/WestElMoudenGardner_11.pdf |archive-date=12 August 2017 |url-status=dead |df=dmy-all |citeseerx=10.1.1.188.3318 }}</ref> while others have argued that kin recognition can also be mediated by biological factors such as facial resemblance and immunogenetic similarity of the major histocompatibility complex (MHC).<ref>{{cite journal | doi = 10.1098/rspb.2012.1279 | volume=279 | title=Social discrimination by quantitative assessment of immunogenetic similarity | year=2012 | journal=Proceedings of the Royal Society B: Biological Sciences | pages=4368–4374 | last1 = Villinger | first1 = J.| issue=1746 | doi-access=free | pmid=22951741 | pmc=3479794 }}</ref> The interaction of these social and biological kin recognition factors was discussed in Lieberman, Tooby, and Cosmides (2007)<ref>{{cite journal | last1 = Lieberman | first1 = D. | last2 = Tooby | first2 = J. | last3 = Cosmides | first3 = L. | title = The architecture of human kin detection | journal = Nature | volume = 445 | issue = 7129| pages = 727–31 | doi = 10.1038/nature05510 | pmid = 17301784 | pmc = 3581061 | date = February 2007 | bibcode = 2007Natur.445..727L }}</ref>

Whatever the proximate mechanisms of kin recognition there is substantial evidence that humans act generally more altruistically to close genetic kin compared to genetic non-kin.<ref name=ReferenceA>Buss, D.M. (2011). Evolutionary Psychology. Monterey: Brooks-Cole.</ref><ref name=Gaulin-2004>Gaulin & McBurney (2004), Evolutionary Psychology, 2nd Ed. NY: Prentice Hall</ref><ref>Workman & Reader (2008), Evolutionary Psychology, 2nd Ed. Cambridge: Cambridge University Press</ref>