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==Ethology== [[File:Elephant seal fight Part-1.jpg|right|thumb|250px|Male [[elephant seal]]s fighting]] [[Ethology|Ethologists]] study aggression as it relates to the interaction and [[evolution]] of animals in natural settings. In such settings aggression can involve bodily contact such as biting, hitting or pushing, but most conflicts are settled by threat displays and intimidating thrusts that cause no physical harm. This form of aggression may include the display of body size, antlers, claws or teeth; stereotyped signals including facial expressions; vocalizations such as bird song; the release of chemicals; and changes in coloration.<ref>Van Staaden, M.J, Searcy, W.A. & Hanlon, R.T. 'Signaling Aggression' in [https://books.google.com/books?id=zkp7nMtMNOgC Aggression] Academic Press, Stephen F. Goodwin, 2011</ref> The term [[agonistic behaviour|agonistic behavior]] is sometimes used to refer to these forms of behavior. Most ethologists believe that aggression confers biological advantages. Aggression may help an animal secure [[territory (animal)|territory]], including resources such as food and water. Aggression between males often occurs to secure mating opportunities, and results in selection of the healthier/more vigorous animal. Aggression may also occur for self-protection or to protect offspring.<ref>{{cite journal |doi=10.1139/z92-150 |title=Functional aspects of maternal aggression in mammals |journal=Canadian Journal of Zoology |volume=70 |issue=6 |pages=1069–77 |year=1992 |last1=Maestripieri |first1=Dario |bibcode=1992CaJZ...70.1069M }}</ref> Aggression between groups of animals may also confer advantage; for example, hostile behavior may force a population of animals into a new territory, where the need to adapt to a new environment may lead to an increase in genetic flexibility.<ref>Psychology- The Science of Behaviour, pg 420, Neil R Clarkson (4th Edition)</ref> ===Between species and groups=== The most apparent type of [[interspecific]] aggression is that observed in the interaction between a [[predator]] and its [[prey]]. However, according to many researchers, [[predation]] is not aggression. A cat does not hiss or arch its back when pursuing a rat, and the active areas in its [[hypothalamus]] resemble those that reflect hunger rather than those that reflect aggression.<ref>Gleitman, Henry, Alan J. Fridlund, and Daniel Reisberg. Psychology. 6th ed. New York: W W Norton and Company, 2004. 431–432.</ref> However, others refer to this behavior as predatory aggression, and point out cases that resemble hostile behavior, such as mouse-killing by rats.<ref>Gendreau, PL & Archer, J. 'Subtypes of Aggression in Humans and Animals', in [https://books.google.com/books/about/Developmental_origins_of_aggression.html?id=XmSfJEl2v4sC Developmental Origins of Aggression], 2005, The Guilford Press.</ref> In [[aggressive mimicry]] a predator has the appearance of a harmless organism or object attractive to the prey; when the prey approaches, the predator attacks. An animal defending against a predator may engage in either "[[Fight-or-flight response|fight or flight]]" or "[[tend and befriend]]" in response to predator attack or threat of attack, depending on its estimate of the predator's strength relative to its own. Alternative defenses include a range of [[antipredator adaptation]]s, including [[alarm signal]]s. An example of an alarm signal is Nerol, a chemical which is found in the mandibular glands of ''[[Trigona fulviventris]]'' individuals.<ref name=":0">{{cite journal |doi=10.1007/BF00990750 |pmid=24413960 |title=Nerol: An alarm substance of the stingless bee, Trigona fulviventris (Hymenoptera: Apidae) |journal=Journal of Chemical Ecology |volume=8 |issue=9 |pages=1167–81 |year=1982 |last1=Johnson |first1=L. K. |last2=Wiemer |first2=D. F. |bibcode=1982JCEco...8.1167J |s2cid=25056451 }}</ref> Release of Nerol by T. fulviventris individuals in the nest has been shown to decrease the number of individuals leaving the nest by fifty percent, as well as increasing aggressive behaviors like biting.<ref name=":0" /> Alarm signals like nerol can also act as attraction signals; in T. fulviventris, individuals that have been captured by a predator may release nerol to attract nest mates, who will proceed to attack or bite the predator.<ref name=":0" /> Aggression between groups is determined partly by willingness to fight, which depends on a number of factors including numerical advantage, distance from home territories, how often the groups encounter each other, competitive abilities, differences in body size, and whose territory is being invaded.<ref>{{cite journal |doi=10.1016/j.jebo.2017.05.004 |title=The logic of animal intergroup conflict: A review |journal=Journal of Economic Behavior and Organization |year=2017 |last1=Rusch |first1=H. |last2=Gavrilets |first2=S.|volume=178 |pages=1014–1030 |s2cid=49359988 |doi-access=free }}</ref> Also, an individual is more likely to become aggressive if other aggressive group members are nearby.<ref>{{cite journal |doi=10.1098/rspb.2006.3626 |pmid=17015327 |pmc=1635503 |jstor=25223670 |title=Numerical assessment affects aggression and competitive ability: A team-fighting strategy for the ant Formica xerophila |journal=Proceedings of the Royal Society B: Biological Sciences |volume=273 |issue=1602 |pages=2737–42 |year=2006 |last1=Tanner |first1=C. J }}</ref> One particular phenomenon – the formation of coordinated coalitions that raid neighboring territories to kill [[conspecific]]s – has only been documented in two species in the animal kingdom: [[Common chimpanzee|'common' chimpanzees]] and [[humans]].<ref>{{cite journal |doi=10.1016/j.cub.2010.04.021 |pmid=20620900 |title=Lethal intergroup aggression leads to territorial expansion in wild chimpanzees |journal=Current Biology |volume=20 |issue=12 |pages=R507–8 |year=2010 |last1=Mitani |first1=John C. |last2=Watts |first2=David P. |last3=Amsler |first3=Sylvia J. |s2cid=6493161 |doi-access=free |bibcode=2010CBio...20.R507M }}</ref> ===Within a group=== Aggression between conspecifics in a group typically involves access to resources and breeding opportunities. One of its most common functions is to establish a [[dominance hierarchy]]. This occurs in many species by aggressive encounters between contending males when they are first together in a common environment.<ref name="adamsonetal2006">{{cite journal |pmid=10574728 |url=http://jeb.biologists.org/cgi/pmidlookup?view=long&pmid=10574728 |year=1999 |last1=Issa |first1=F. A. |title=Dominance hierarchy formation in juvenile crayfish procambarus clarkii |journal=The Journal of Experimental Biology |volume=202 |pages=3497–506 |last2=Adamson |first2=D. J. |last3=Edwards |first3=D. H. |issue=24|doi = 10.1242/jeb.202.24.3497| bibcode=1999JExpB.202.3497I |url-access=subscription }}</ref> Usually the more aggressive animals become the more dominant.<ref>{{cite journal |doi=10.1016/j.beproc.2006.05.004 |pmid=16815645 |title=Social relationships in a herd of Sorraia horses |journal=Behavioural Processes |volume=73 |issue=2 |pages=170–7 |year=2006 |last1=Heitor |first1=Filipa |last2=Oom |first2=Maria do Mar |last3=Vicente |first3=Luís |s2cid=24008518 }}</ref><ref>{{cite journal |doi=10.1086/503445 |pmid=16615035 |title=Individual Variation in Social Aggression and the Probability of Inheritance: Theory and a Field Test |journal=The American Naturalist |volume=167 |issue=6 |pages=837–52 |year=2006 |last1=Cant |first1=Michael A. |last2=Llop |first2=Justine B. |last3=Field |first3=Jeremy |bibcode=2006ANat..167..837C |hdl=10871/26263 |s2cid=12094679 |url=https://ore.exeter.ac.uk/repository/bitstream/10871/26263/1/CantetalAggression06AmNat.pdf |hdl-access=free }}</ref> In test situations, most of the conspecific aggression ceases about 24 hours after the group of animals is brought together.<ref name="adamsonetal2006"/><ref>{{cite journal |pmid=16869278 |year=2006 |last1=Bragin |first1=A. V. |title=The experimental model of establishment and maintenance of social hierarchy in laboratory mice |journal=Zhurnal Vysshei Nervnoi Deiatelnosti imeni I P Pavlova |volume=56 |issue=3 |pages=412–9 |last2=Osadchuk |first2=L. V. |last3=Osadchuk |first3=A. V. }}</ref> Aggression has been defined from this viewpoint as "behavior which is intended to increase the social dominance of the organism relative to the dominance position of other organisms".<ref name="Ferguson & Beaver, 2009">{{cite journal |doi=10.1016/j.avb.2009.03.005 |title=Natural born killers: The genetic origins of extreme violence |journal=Aggression and Violent Behavior |volume=14 |issue=5 |pages=286–94 |year=2009 |last1=Ferguson |first1=Christopher J. |last2=Beaver |first2=Kevin M. }}</ref> Losing confrontations may be called [[social defeat]], and winning or losing is associated with a range of practical and psychological consequences.<ref>{{cite journal |doi=10.1017/S146479310500686X |pmid=16460581 |title=Modulation of aggressive behaviour by fighting experience: Mechanisms and contest outcomes |journal=Biological Reviews |volume=81 |issue=1 |pages=33–74 |year=2005 |last1=Hsu |first1=Yuying |last2=Earley |first2=Ryan L. |last3=Wolf |first3=Larry L. |s2cid=14284236 |doi-access=free }}</ref> Conflicts between animals occur in many contexts, such as between potential mating partners, between parents and offspring, between siblings and between competitors for resources. Group-living animals may dispute over the direction of travel or the allocation of time to joint activities. Various factors limit the escalation of aggression, including communicative displays, conventions, and routines. In addition, following aggressive incidents, various forms of [[conflict resolution]] have been observed in mammalian species, particularly in gregarious primates. These can mitigate or repair possible adverse consequences, especially for the recipient of aggression who may become vulnerable to attacks by other members of a group. Conciliatory acts vary by species and may involve specific gestures or simply more proximity and interaction between the individuals involved. However, conflicts over food are rarely followed by post conflict reunions, even though they are the most frequent type in foraging primates.<ref>{{cite journal |doi=10.1006/anbe.2002.3071 |title=Conflict resolution following aggression in gregarious animals: A predictive framework |journal=Animal Behaviour |volume=64 |issue=3 |pages=325–43 |year=2002 |last1=Aureli |first1=Filippo |last2=Cords |first2=Marina |last3=Van Schaik |first3=Carel P. |s2cid=54361369 }}</ref> Other questions that have been considered in the study of primate aggression, including in humans, is how aggression affects the organization of a group, what costs are incurred by aggression, and why some primates avoid aggressive behavior.<ref>Silverberg, James; J. Patrick Gray (1992) ''[https://books.google.com/books?id=5CQW4vPNH-EC Aggression and Peacefulness in Humans and Other Primates]'' {{ISBN|0-19-507119-0}}</ref> For example, [[Bonobo|bonobo chimpanzee]] groups are known for low levels of aggression within a partially [[matriarchal]] society. [[Captivity (animal)|Captive]] animals including primates may show abnormal levels of social aggression and self-harm that are related to aspects of the physical or social environment; this depends on the species and individual factors such as gender, age and background (e.g., raised wild or captive).<ref>{{cite journal |doi=10.1016/j.neubiorev.2005.05.002 |pmid=16055188 |title=Enrichment and aggression in primates |journal=Neuroscience & Biobehavioral Reviews |volume=30 |issue=3 |pages=413–36 |year=2006 |last1=Honess |first1=P.E. |last2=Marin |first2=C.M. |s2cid=33130527 }}</ref> ===Aggression, fear and curiosity=== Within ethology, it has long been recognized that there is a relation between aggression, [[fear]], and [[curiosity]].<ref>{{Cite book|last=Hinde|first=R.A.|title=Animal Behaviour: A Synthesis of Ethology and Comparative Psychology (2nd Ed.)|publisher=McGraw-Hill|year=1970|location=New York, NY}}</ref> A [[cognitive science|cognitive]] approach to this relationship puts aggression in the broader context of [[cognitive dissonance|inconsistency reduction]], and proposes that aggressive behavior is caused by an inconsistency between a desired, or expected, situation and the actually perceived situation (e.g., "[[Frustration–aggression hypothesis|frustration]]"), and functions to forcefully [[Manipulation (psychology)|manipulate]] the perception into matching the expected situation.<ref>{{Cite book|last=Hebb|first=D.O.|title=The Organisation of Behavior|publisher=Wiley|year=1949|location=New York, NY}}</ref><ref name=":Archer"/><ref name=":Kampen">{{cite journal | last = van Kampen | first = H.S. | year = 2019 | title = The principle of consistency and the cause and function of behaviour | doi = 10.1016/j.beproc.2018.12.013 | journal = Behavioural Processes | volume = 159 | pages = 42–54 | pmid = 30562561 | s2cid = 56478466 }}</ref> In this approach, when the inconsistency between perception and expectancy is small, learning as a result of curiosity reduces inconsistency by updating expectancy to match perception. If the inconsistency is larger, fear or aggressive behavior may be employed to alter the perception in order to make it match expectancy, depending on the size of the inconsistency as well as the specific context. Uninhibited fear results in fleeing, thereby removing the inconsistent stimulus from the perceptual field and resolving the inconsistency. In some cases thwarted escape may trigger aggressive behavior in an attempt to remove the thwarting stimulus.<ref name=":Kampen"/>
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