Editing Ethology (section)

== Social behaviour ==

Several animal species, including humans, tend to live in groups. [[Group size measures|Group size]] is a major aspect of their social environment. [[Social relation|Social life]] is probably a complex and effective survival strategy. It may be regarded as a sort of [[symbiosis]] among individuals of the same species: a [[society]] is composed of a group of individuals belonging to the same species living within well-defined rules on [[food]] management, role assignments and reciprocal dependence.<ref name="Mandal 2015">{{cite book |last=Mandal |first=F. B.|year=2015 |title=Textbook of Animal Behaviour |location=India |publisher=PHI Learning |isbn=978-812035148-6 |pages=191–193}}</ref>

When [[biologist]]s interested in [[evolution theory]] first started examining social behaviour, some apparently unanswerable questions arose, such as how the birth of [[Reproduce|sterile]] [[caste]]s, like in [[bee]]s, could be explained through an evolving mechanism that emphasizes the reproductive success of as many individuals as possible, or why, amongst animals living in small groups like [[squirrel]]s, an individual would risk its own life to save the rest of the group. These behaviours may be examples of [[Altruism (biology)|altruism]].<ref>{{cite book |author=Cummings, Mark |author2=Zahn-Waxler, Carolyn  |author3=Iannotti, Ronald |title=Altruism and aggression: biological and social origins |url=https://archive.org/details/altruismaggressi00zahn |url-access=limited |year=1991 |publisher=Cambridge University Press |isbn=978-0-521-42367-0 |page=[https://archive.org/details/altruismaggressi00zahn/page/n21 7]}}</ref> Not all behaviours are altruistic, as indicated by the table below. For example, revengeful behaviour was at one point claimed to have been observed exclusively in ''[[Homo sapiens]]''. However, other species have been reported to be vengeful including chimpanzees,<ref name="McCullough2008">{{cite book |last=McCullough |first=Michael E. |author-link=Michael McCullough (psychologist) |title=Beyond Revenge: The Evolution of the Forgiveness Instinct |url=https://books.google.com/books?id=daomTGYZuW4C&pg=PA79 |year=2008 |publisher=John Wiley & Sons |isbn=978-0-470-26215-3 |pages=79–80}}</ref> as well as anecdotal reports of vengeful camels.<ref name="Waal2001">{{cite book |last=De Waal |first=Frans |author-link=Frans de Waal |title=The Ape and the Sushi Master: Cultural Reflections by a Primatologist |url=https://archive.org/details/apesushimastercu0000waal |url-access=registration |access-date=27 December 2016 |year=2001 |publisher=Basic Books |isbn=978-0-465-04176-3 |page=[https://archive.org/details/apesushimastercu0000waal/page/338 338]}}</ref>

{| class="wikitable" style="margin: 1em auto;" text-align:center;"
|+ Classification of social behaviours<ref name="Mandal 2015"/>
|-
! Type of behaviour
! Effect on the donor
! Effect on the receiver
|-
| [[Egotism|Egoistic]]
| Neutral to Increases fitness
| Decreases fitness
|-
| [[cooperation|Cooperative]]
| Neutral to Increases fitness
| Neutral to Increases fitness
|-
| [[Altruism (biology)|Altruistic]]
| Decreases fitness
| Neutral to Increases fitness
|-
| [[Revenge]]ful
| Decreases fitness
| Decreases fitness
|}

[[Altruism (biology)|Altruistic]] behaviour has been explained by the [[gene-centered view of evolution|gene-centred view of evolution]].<ref>{{Cite journal |last=Dawkins |first=Richard |author-link=Richard Dawkins| date=January 1979 |title=Twelve Misunderstandings of Kin Selection |url=http://onlinelibrary.wiley.com/doi/10.1111/j.1439-0310.1979.tb00682.x/full |journal=Zeitschrift für Tierpsychologie |volume=51 |issue=2 |pages=184–200 |doi=10.1111/j.1439-0310.1979.tb00682.x|bibcode=1979Ethol..51..184D }}</ref><ref>{{Cite journal |last=Ågren |first=J. Arvid |date=2016 |title=Selfish genetic elements and the gene's-eye view of evolution |journal=Current Zoology |volume=62 |issue=6 |pages=659–665 |doi=10.1093/cz/zow102 |pmid=29491953 |pmc=5804262 |issn=1674-5507}}</ref>

=== Benefits and costs of group living ===

One advantage of group living is decreased predation. If the number of predator attacks stays the same despite increasing prey group size, each prey has a reduced risk of predator attacks through the dilution effect.<ref name=Davies2012>{{cite book |last1=Davies |first1=Nicholas B. |author-link1=Nicholas Barry Davies |author2=Krebs, John R. |author-link2=John Krebs, Baron Krebs |author3=West, Stuart A. |author-link3=Stuart West |title=An Introduction to Behavioural Ecology |url=https://books.google.com/books?id=G9mXO5asWi8C |edition=4th |year=2012 |publisher=John Wiley & Sons |isbn=978-1-4443-3949-9}}</ref>{{Page needed|date=December 2016}} Further, according to the [[selfish herd theory]], the fitness benefits associated with group living vary depending on the location of an individual within the group. The theory suggests that conspecifics positioned at the centre of a group will reduce the likelihood predations while those at the periphery will become more vulnerable to attack.<ref>{{Cite journal |last=Hamilton |first=W. D. |author-link=W. D. Hamilton |title=Geometry for the Selfish Herd |journal=Journal of Theoretical Biology |volume=31 |issue=2 |pages=295–311 |doi=10.1016/0022-5193(71)90189-5|pmid=5104951 |year=1971 |bibcode=1971JThBi..31..295H }}</ref> In groups, prey can also actively reduce their predation risk through more effective defence tactics, or through earlier detection of predators through increased vigilance.<ref name=Davies2012/>

Another advantage of group living is an increased ability to forage for food. Group members may exchange information about food sources, facilitating the process of [[Foraging#Group foraging|resource location]].<ref name=Davies2012/>{{Page needed |date=December 2016}} Honeybees are a notable example of this, using the [[waggle dance]] to communicate the location of flowers to the rest of their hive.<ref>{{cite journal |author1=Riley, J. |author2=Greggers, U. |author3=Smith, A. |author4=Reynolds, D. R. |author5=Menzel, R.  |year=2005 |title=The flight paths of honeybees recruited by the waggle dance |bibcode=2005Natur.435..205R |journal=Nature |volume=435 |issue=7039 |pages=205–207 |doi=10.1038/nature03526 |pmid=15889092|s2cid=4413962 }}</ref> Predators also receive benefits from [[Cooperative hunting|hunting in groups]], through using better strategies and being able to take down larger prey.<ref name=Davies2012/>{{Page needed |date=December 2016}}

Some disadvantages accompany living in groups. Living in close proximity to other animals can facilitate the transmission of parasites and disease, and groups that are too large may also experience greater competition for resources and mates.<ref>{{cite web |last=Rathads |first=Triana |url=http://www.sciences360.com/index.php/a-look-at-animal-social-groups-6-23511/ |title=A Look at Animal Social Groups |website=Science 360 |date=29 August 2007 |access-date=22 April 2014 |url-status=dead |archive-url=https://web.archive.org/web/20140508030759/http://www.sciences360.com/index.php/a-look-at-animal-social-groups-6-23511/ |archive-date=8 May 2014}}</ref>

=== Group size ===

Theoretically, social animals should have optimal group sizes that maximize the benefits and minimize the costs of group living. However, in nature, most groups are stable at slightly larger than optimal sizes.<ref name=Davies2012/>{{Page needed |date=December 2016}} Because it generally benefits an individual to join an optimally-sized group, despite slightly decreasing the advantage for all members, groups may continue to increase in size until it is more advantageous to remain alone than to join an overly full group.<ref>{{cite journal | last1=Sibley | first1=R. M. | year=1983 | title=Optimal group size is unstable | doi=10.1016/s0003-3472(83)80250-4 | journal=Animal Behaviour | volume=31 | issue=3 | pages=947–948 | s2cid=54387192 }}</ref>
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