Editing Aggression (section)

==Society and culture==
[[Humans]] share aspects of aggression with non-human animals, and have specific aspects and complexity related to factors such as genetics, early development, social learning and flexibility, culture and morals.
Konrad Lorenz stated in his 1963 classic, ''On Aggression,'' that human behavior is shaped by four main, survival-seeking animal drives. Taken together, these drives—hunger, fear, reproduction, and aggression—achieve natural selection.<ref>Konrad Lorenz, ''On Aggression'' (1963).{{page needed|date=February 2017}}</ref> [[E. O. Wilson]] elaborated in ''On Human Nature'' that aggression is, typically, a means of gaining control over resources. Aggression is, thus, aggravated during times when high population densities generate resource shortages.<ref>E.O. Wilson, ''On Human Nature'' (Harvard, 1978) pp.101–107.</ref> According to Richard Leakey and his colleagues, aggression in humans has also increased by becoming more interested in ownership and by defending his or her property.<ref>Leakey, R.,& Lewin, R. (1978). ''People of the lake''. New York: Anchor Press/Doubleday.</ref> However, [[UNESCO]] adopted the Seville [[Seville Statement on Violence|Statement of Violence]] in 1989 that refuted claims, by evolutionary scientists, that genetics by itself was the sole cause of aggression.<ref>UNESCO, (1989). The Seville Statement, Retrieved: http://www.unesco.org/cpp/uk/declarations/seville.pdf {{Webarchive|url=https://web.archive.org/web/20130812082020/http://www.unesco.org/cpp/uk/declarations/seville.pdf |date=12 August 2013 }}</ref><ref>UNESCO Prize for Peace Education, (1989), Retrieved:http://www.demilitarisation.org/IMG/article_PDF/Seville-Statement-UNESCO-1989_a143.pdf</ref>

Social and cultural aspects may significantly interfere with the distinct expression of aggressiveness. For example, a high population density, when associated with a decrease of available resources, might be a significant intervening variable for the occurrence of violent acts.<ref name="Bond04" />

===Culture===
{{copy edit|section|for=proper paragraphing. Excessively long, run-on paragraphs need to be split into multiple paragraphs of moderate length|date=September 2024}}
Culture is one factor that plays a role in aggression. [[Tribal]] or [[band society|band]] societies existing before or outside of modern [[state (polity)|states]] have sometimes been depicted as peaceful '[[noble savage]]s'. The [[ǃKung people]] were described as 'The Harmless People' in a popular work by [[Elizabeth Marshall Thomas]] in 1958,<ref>Thomas, E.M. (1958). ''[https://books.google.com/books/about/The_harmless_people.html?id=n_lOAAAAMAAJ The harmless people]''. New York: Vintage Books.{{page needed|date=February 2017}}</ref> while Lawrence Keeley's 1996 [[War Before Civilization]] suggested that regular [[warfare]] without modern technology was conducted by most groups throughout human history, including most [[Indigenous peoples of the Americas|Native American]] tribes.<ref>Keeley, L.H. (1996). ''[[War Before Civilization]]: The myth of the peaceful savage''. New York: Oxford University Press.</ref> Studies of [[hunter-gatherers]] show a range of different societies. In general, aggression, conflict and violence sometimes occur, but direct confrontation is generally avoided and conflict is socially managed by a variety of verbal and non-verbal methods. Different rates of aggression or violence, currently or in the past, within or between groups, have been linked to the structuring of societies and environmental conditions influencing factors such as [[resource]] or [[property]] acquisition, [[Land (economics)|land]] and [[List of subsistence techniques|subsistence]] techniques, and [[population change]].<ref>Lomas, W. (2009) [http://ir.lib.uwo.ca/cgi/viewcontent.cgi?article=1205&context=totem Conflict, Violence, and Conflict Resolution in Hunting and Gathering Societies] Totem: The University of Western Ontario Journal of Anthropology, Volume 17, Issue 1, Article 13</ref>

American psychologist [[Peter Gray (psychologist)|Peter Gray]] hypothesizes that band hunter-gatherer societies are able to reduce aggression while maintaining relatively peaceful, [[egalitarian]] relations between members through various methods, such as fostering a [[playful]] spirit in all areas of life, the use of humor to counter the tendency of any one person to dominate the group, and non-coercive or "indulgent" child-rearing practices. Gray likens hunter-gatherer bands to social play groups, while stressing that such play is not frivolous or even easy at all times.<ref name=PlayFoundation>{{cite journal |author=Gray, Peter |date=Spring 2009 |title=Play as a Foundation for Hunter-Gatherer Social Existence |journal=American Journal of Play |volume=1 |issue=4 |pages=476–522 |url=http://www.journalofplay.org/sites/www.journalofplay.org/files/pdf-articles/1-4-article-hunter-gatherer-social-existence.pdf |archive-url=https://web.archive.org/web/20131024201853/http://www.journalofplay.org/sites/www.journalofplay.org/files/pdf-articles/1-4-article-hunter-gatherer-social-existence.pdf |url-status=dead |archive-date=24 October 2013 }}</ref> According to Gray, "Social play—that is, play involving more than one player—is necessarily egalitarian. It always requires a suspension of aggression and dominance along with a heightened sensitivity to the needs and desires of the other players".<ref>{{cite web |author=Gray, Peter |date=16 May 2011 |title=How Hunter-Gatherers Maintained Their Egalitarian Ways |website=Psychology Today |url=https://www.psychologytoday.com/blog/freedom-learn/201105/how-hunter-gatherers-maintained-their-egalitarian-ways}}</ref>

Joan Durrant at the [[University of Manitoba]] writes that a number of studies have found [[physical punishment]] to be associated with "higher levels of aggression against parents, siblings, peers and spouses", even when controlling for other factors.<ref name=Lessons>{{cite journal |doi=10.1503/cmaj.101314 |pmid=22311946 |pmc=3447048 |title=Physical punishment of children: Lessons from 20 years of research |journal=Canadian Medical Association Journal |volume=184 |issue=12 |pages=1373–7 |year=2012 |last1=Durrant |first1=J. |last2=Ensom |first2=R. }}</ref>

According to [[Elizabeth Gershoff]] at the [[University of Texas at Austin]], the more that children are physically punished, the more likely they are as adults to act violently towards family members, including intimate partners.<ref>{{cite book |author=Gershoff, E.T. |date=2008 |title=Report on Physical Punishment in the United States: What Research Tells Us About Its Effects on Children |location=Columbus, OH |publisher=Center for Effective Discipline |page=16 |url=http://www.phoenixchildrens.org/sites/default/files/PDFs/principles_and_practices-of_effective_discipline.pdf |access-date=15 December 2015 |archive-url=https://web.archive.org/web/20160127213730/http://www.phoenixchildrens.org/sites/default/files/PDFs/principles_and_practices-of_effective_discipline.pdf |archive-date=27 January 2016 |url-status=dead  }}</ref>

In countries where physical punishment of children is perceived as being more culturally accepted, it is less strongly associated with increased aggression; however, physical punishment has been found to predict some increase in child aggression regardless of culture.<ref name=SocialSciences>[http://www.encyclopedia.com/doc/1G2-3045300461.html "Corporal Punishment"] (2008). ''International Encyclopedia of the Social Sciences''.</ref> While these associations do not prove [[causality]], a number of [[longitudinal study|longitudinal studies]] suggest that the experience of physical punishment has a direct causal effect on later aggressive behaviors.<ref name=Lessons/> In examining several longitudinal studies that investigated the path from disciplinary [[spanking]] to aggression in children from preschool age through adolescence, Gershoff concluded: "Spanking consistently predicted increases in children's aggression over time, regardless of how aggressive children were when the spanking occurred".<ref name=Development>{{cite journal |doi=10.1111/cdep.12038 |pmid=24039629 |pmc=3768154 |title=Spanking and Child Development: We Know Enough Now to Stop Hitting Our Children |journal=Child Development Perspectives |volume=7 |issue=3 |pages=133–137 |year=2013 |last1=Gershoff |first1=Elizabeth T. }}</ref>

Similar results were found by Catherine Taylor at [[Tulane University]] in 2010.<ref>{{cite journal |doi=10.1542/peds.2009-2678 |pmid=20385647 |pmc=5094178 |title=Mothers' Spanking of 3-Year-Old Children and Subsequent Risk of Children's Aggressive Behavior |journal=Pediatrics |volume=125 |issue=5 |pages=e1057–65 |year=2010 |last1=Taylor |first1=C. A. |last2=Manganello |first2=J. A. |last3=Lee |first3=S. J. |last4=Rice |first4=J. C. }}</ref> Family violence researcher [[Murray A. Straus]] argues, "There are many reasons this evidence has been ignored. One of the most important is the belief that spanking is more effective than nonviolent discipline and is, therefore, sometimes necessary, despite the risk of harmful side effects".<ref>
{{cite book |author1=Straus, Murray A. |author2=Douglas, Emily M. |author3=Madeiros, Rose Ann |title=The Primordial Violence: Spanking Children, Psychological Development, Violence, and Crime |location=New York |publisher=Routledge |date=2013 |page=81|isbn=978-1-84872-953-7 |url=https://books.google.com/books?id=gZTCAAAAQBAJ}}</ref>

Analyzing aggression culturally or politically is complicated by the fact that the [[labeling theory|label]] 'aggressive' can itself be used as a way of asserting a judgement from a particular point of view.{{according to whom |date=December 2015}} Whether a [[coercive]] or violent method of social control is perceived as aggression&nbsp;– or as legitimate versus illegitimate aggression&nbsp;– depends on the position of the relevant parties in relation to the social order of their culture. This in turn can relate to factors such as: norms for coordinating actions and dividing resources; what is considered self-defense or provocation; attitudes towards 'outsiders', attitudes towards specific groups such as women, disabled people or those with lower status; the availability of alternative conflict resolution strategies; [[trade]] interdependence and [[collective security]] pacts; fears and impulses; and ultimate goals regarding material and social outcomes.<ref name="Bond04">Bond, MH. (2004) 'Aggression and culture', in [https://books.google.com/books?id=UriYBuiH_FkC Encyclopedia of applied psychology], Volume 1.</ref>

[[Cross-cultural]] research has found differences in attitudes towards aggression in different cultures. In one questionnaire study of university students, in addition to men overall justifying some types of aggression more than women, United States respondents justified defensive physical aggression more readily than Japanese or Spanish respondents, whereas Japanese students preferred direct verbal aggression (but not indirect) more than their American and Spanish counterparts.<ref>{{cite journal |doi=10.1002/(SICI)1098-2337(1999)25:3<185::AID-AB3>3.0.CO;2-K |title=Justification of interpersonal aggression in Japanese, American, and Spanish students |journal=Aggressive Behavior |volume=25 |issue=3 |pages=185–95 |year=1999 |last1=Fujihara |first1=Takehiro |last2=Kohyama |first2=Takaya |last3=Andreu |first3=J. Manuel |last4=Ramirez |first4=J. Martin |s2cid=145166936 }}</ref>

Within American culture, [[Southern United States|southern]] men were shown in a study on university students to be more affected and to respond more aggressively than northerners when randomly insulted after being bumped into, which was theoretically related to a traditional [[Culture of honor (Southern United States)|culture of honor in the Southern United States]], or "[[Face (sociological concept)|saving face]]."<ref>{{cite journal |doi=10.1037/0022-3514.70.5.945 |pmid=8656339 |title=Insult, aggression, and the southern culture of honor: An "experimental ethnography." |journal=Journal of Personality and Social Psychology |volume=70 |issue=5 |pages=945–59 |year=1996 |last1=Cohen |first1=Dov |last2=Nisbett |first2=Richard E. |last3=Bowdle |first3=Brian F. |last4=Schwarz |first4=Norbert |hdl=2027.42/92155 |url=https://deepblue.lib.umich.edu/bitstream/2027.42/92155/1/InsultAggressionAndTheSouthernCulture.pdf |hdl-access=free }}</ref> Other cultural themes sometimes applied to the study of aggression include [[individualistic]] versus [[Collectivism and individualism|collectivist]] styles, which may relate, for example, to whether disputes are responded to with open competition or by accommodating and [[Conflict avoidance|avoiding conflicts]].

In a study including 62 countries school principals reported aggressive student behavior more often the more individualist, and hence less collectivist, their country's culture.<ref>{{cite journal |doi=10.1002/ab.21472 |pmid=23494751 |title=The Relationship Between Cultural Individualism-Collectivism and Student Aggression Across 62 Countries |journal=Aggressive Behavior |volume=39 |issue=3 |pages=182–200 |year=2013 |last1=Bergmüller |first1=Silvia }}</ref> Other comparisons made in relation to aggression or war include [[democracy|democratic]] versus [[authoritarianism|authoritarian]] [[political systems]] and [[egalitarian]] versus [[Social stratification|stratified]] societies.<ref name="Bond04" />

The [[economic system]] known as [[capitalism]] has been viewed by some as reliant on the [[lever]]aging of human competitiveness and aggression in pursuit of resources and trade, which has been considered in both positive and negative terms.<ref>Nolan, P. (2007) [https://books.google.com/books/about/Capitalism_and_freedom.html?id=pg6h0_7xRnkC Capitalism and freedom: the contradictory character of globalisation] From page 2. Anthem Studies in Development and Globalization, Anthem Press</ref> Attitudes about the social acceptability of particular acts or targets of aggression are also important factors. This can be highly controversial, as for example in disputes between religions or nation states, for example in regard to the [[Arab–Israeli conflict]].<ref>{{cite journal |doi=10.1016/j.ijintrel.2004.03.004 |title=Aggression and violence among Jewish and Arab Youth in Israel |journal=International Journal of Intercultural Relations |volume=28 |issue=2 |pages=93–109 |year=2004 |last1=Sherer |first1=Moshe |last2=Karnieli-Miller |first2=Orit }}</ref><ref name=amjad>{{cite journal |doi=10.1002/ab.20325 |pmid=19790255 |title=Identifying and changing the normative beliefs about aggression which lead young Muslim adults to join extremist anti-Semitic groups in Pakistan |journal=Aggressive Behavior |volume=35 |issue=6 |pages=514–9 |year=2009 |last1=Amjad |first1=Naumana |last2=Wood |first2=Alex M. |citeseerx=10.1.1.332.6476 }}</ref>

====Media====
{{Main|Media violence research}}
Some scholars believe that behaviors like aggression may be partially learned by watching and imitating people's behavior, while other researchers have concluded that the media may have some small effects on aggression.<ref>Akert, M. Robin, Aronson, E., and Wilson, D.T. "Social Psychology", 5th Edition. Pearson Education, Inc. 2005{{page needed|date=February 2017}}</ref> There is also research questioning this view.<ref>Freedman, J. (2002). ''[https://books.google.com/books/about/Media_violence_and_its_effect_on_aggress.html?id=GL9DMwoW2P8C Media violence and its effect on aggression: Assessing the scientific evidence]''. Toronto: University of Toronto Press.</ref> For instance, a long-term outcome study of youth found no long-term relationship between playing violent video games and youth violence or bullying.<ref>Christopher J. Ferguson, (2010) "[http://www.tamiu.edu/~cferguson/Video%20Games%201%20Year.pdf Video Games and Youth Violence: A Prospective Analysis in Adolescents] {{webarchive|url=https://web.archive.org/web/20120525061300/http://www.tamiu.edu/~cferguson/Video%20Games%201%20Year.pdf |date=25 May 2012 }}", ''Journal of Youth and Adolescence''</ref>

One study suggested there is a smaller effect of violent video games on aggression than has been found with [[Research on the effects of violence in mass media|television violence]] on aggression. This effect is positively associated with type of game violence and [[Inverse relationship|negatively associated]] to time spent playing the games.<ref>{{cite journal |doi=10.1093/hcr/27.3.409 |title=The effects of violent video games on aggression. A meta-analysis |journal=Human Communication Research |volume=27 |issue=3 |pages=409–31 |year=2001 |last1=Sherry |first1=J. |doi-broken-date=11 January 2025 |s2cid=6322160 }}</ref> The author concluded that insufficient evidence exists to link video game violence with aggression. However, another study suggested links to aggressive behavior.<ref>{{cite journal |doi=10.1037/0022-3514.78.4.772 |pmid=10794380 |title=Video games and aggressive thoughts, feelings, and behavior in the laboratory and in life |journal=Journal of Personality and Social Psychology |volume=78 |issue=4 |pages=772–90 |year=2000 |last1=Anderson |first1=Craig A. |last2=Dill |first2=Karen E. |citeseerx=10.1.1.1006.1548 }}</ref>

===Children===
The frequency of physical aggression in humans peaks at around 2–3 years of age. It then declines gradually on average.<ref>{{cite journal |doi=10.1080/016502500383232 |title=The development of aggressive behaviour during childhood: What have we learned in the past century? |journal=International Journal of Behavioral Development |volume=24 |issue=2 |pages=129–41 |year=2000 |last1=Tremblay |first1=Richard E. |citeseerx=10.1.1.487.7070 |s2cid=145617291 }}</ref><ref>{{cite journal |doi=10.1111/j.1467-8624.2004.00755.x |pmid=15369529 |title=Developmental Trajectories of Externalizing Behaviors in Childhood and Adolescence |journal=Child Development |volume=75 |issue=5 |pages=1523–37 |year=2004 |last1=Bongers |first1=Ilja L. |last2=Koot |first2=Hans M. |last3=Van Der Ende |first3=Jan |last4=Verhulst |first4=Frank C. |s2cid=12514300 |url=https://research.vu.nl/en/publications/a99fc7fa-b013-4b5c-99d9-1586ea705856 }}</ref> These observations suggest that physical aggression is not only a learned behavior but that development provides opportunities for the learning and biological development of self-regulation. However, a small subset of children fail to acquire all the necessary self-regulatory abilities and tend to show atypical levels of physical aggression across development. They may be at risk for later violent behavior or, conversely, lack of aggression that may be considered necessary within society.

However, some findings suggest that early aggression does not necessarily lead to aggression later on, although the course through early childhood is an important predictor of outcomes in middle childhood. In addition, physical aggression that continues is likely occurring in the context of family adversity, including socioeconomic factors. Moreover, 'opposition' and 'status violations' in childhood appear to be more strongly linked to social problems in adulthood than simply aggressive antisocial behavior.<ref>{{cite journal |doi=10.1111/j.0037-976X.2004.00312.x |pmid=15667346 |journal=Monographs of the Society for Research in Child Development |volume=69 |issue=4 |pages=vii, 1–129 |year=2004 |author1=NICHD Early Child Care Research Network. |title=Trajectories of physical aggression from toddlerhood to middle childhood: Predictors, correlates, and outcomes |doi-broken-date=11 January 2025 }}</ref><ref>{{cite journal |doi=10.1017/S0033291707002309 |pmid=18047767 |title=Predicting young adult social functioning from developmental trajectories of externalizing behaviour |journal=Psychological Medicine |volume=38 |issue=7 |pages=989–99 |year=2007 |last1=Bongers |first1=I. L. |last2=Koot |first2=H. M. |last3=Van Der Ende |first3=J. |last4=Verhulst |first4=F. C. |citeseerx=10.1.1.572.4309 |s2cid=6218999 }}</ref> Social learning through interactions in early childhood has been seen as a building block for levels of aggression which play a crucial role in the development of peer relationships in middle childhood.<ref>{{cite journal |last=Schellenberg |first=R. |year=2000 |title=Aggressive personality: When does it develop and why? |journal=Virginia Counselors Journal | volume=26 |pages=67–76 }}</ref> Overall, an interplay of biological, social and environmental factors can be considered.<ref>{{cite book |editor=Tremblay, Richard E |editor2=Hartup, Willard W. |editor3=Archer, John |year=2005 |title=Developmental Origins of Aggression |location=New York |publisher=The Guilford Press |isbn=978-1-59385-110-1|url=https://books.google.com/books?id=XmSfJEl2v4sC}}</ref> Some research indicates that changes in the weather can increase the likelihood of children exhibiting deviant behavior.<ref>{{cite book|last1=Dabb|first1=C|title=The relationship between weather and children's behavior: a study of teacher perceptions|url = https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=3651&context=etd|publisher = USU Thesis|date=May 1997}}</ref>

====Typical expectations====
* Young children preparing to enter kindergarten need to develop the socially important skill of being [[assertive]]. Examples of assertiveness include asking others for information, initiating conversation, or being able to respond to [[peer pressure]].
* In contrast, some young children use aggressive behavior, such as hitting or biting, as a form of communication.
* Aggressive behavior can impede learning as a skill deficit, while assertive behavior can facilitate learning. However, with young children, aggressive behavior is developmentally appropriate and can lead to opportunities of building conflict resolution and communication skills.
* By school age, children should learn more socially appropriate forms of communicating such as expressing themselves through verbal or written language; if they have not, this behavior may signify a disability or developmental delay.

====Aggression triggers====
* [[Phobia|Physical fear of others]]
* [[Dysfunctional family|Family difficulties]]
* [[learning disorder|Learning]], [[neurological disorder|neurological]], or [[conduct disorder|conduct/behavior disorders]]
* [[Psychological trauma]]

The [[Bobo doll experiment]] was conducted by Albert Bandura in 1961. In this work, Bandura found that children exposed to an aggressive adult model acted more aggressively than those who were exposed to a nonaggressive adult model. This experiment suggests that anyone who comes in contact with and interacts with children can affect the way they react and handle situations.<ref>{{cite journal |doi=10.1037/h0045925 |title=Transmission of aggression through imitation of aggressive models |journal=The Journal of Abnormal and Social Psychology |volume=63 |issue=3 |pages=575–82 |year=1961 |last1=Bandura |first1=Albert |last2=Ross |first2=Dorothea |last3=Ross |first3=Sheila A. |s2cid=18361226 |pmid=13864605}}</ref>

;Summary points from recommendations by national associations:
* [[American Academy of Pediatrics]] (2011): "The best way to prevent aggressive behavior is to give your child a stable, secure home life with firm, loving discipline and full-time supervision during the toddler and preschool years. Everyone who cares for your child should be a good role model and agree on the rules he's expected to observe as well as the response to use if he disobeys."<ref>American Academy of Pediatrics (2011) [http://www.healthychildren.org/English/ages-stages/toddler/Pages/Aggressive-Behavior.aspx Ages & Stages: Aggressive Behavior] HealthChildren.org, retrieved January 2012</ref>
* [[National Association of School Psychologists]] (2008): "Proactive aggression is typically reasoned, unemotional, and focused on acquiring some goal. For example, a bully wants peer approval and victim submission, and gang members want status and control. In contrast, reactive aggression is frequently highly emotional and is often the result of biased or deficient cognitive processing on the part of the student."<ref>National Association of School Psychologists (2008) [https://web.archive.org/web/20101205043644/http://www.nasponline.org/resources/principals/Angry%20and%20Aggressive%20Students-NASSP%20Jan%2008.pdf Angry and Aggressive Students]</ref>

===Gender===
{{See also|Sex and psychology}}
Gender is a factor that plays a role in both human and animal aggression. Males are historically believed to be generally more physically aggressive than females from an early age,<ref>Coie, J.D. & Dodge, K.A. (1997). Aggression and antisocial behavior. In W. Damon & N. Eisenberg (Eds). ''Handbook of Child Psychology, Vol. 3: Social, emotional and personality development''</ref><ref>Maccoby. E.E. & Jacklin. C.N. (1974). ''[https://books.google.com/books/about/The_Psychology_of_Sex_Differences_Annota.html?id=2g63eUFP7VkC The psychology of sex differences]'', Stanford: Stanford University Press.
</ref> and men commit the vast majority of murders (Buss 2005). This is one of the most robust and reliable behavioral sex differences, and it has been found across many different age groups and cultures. However, some [[empirical studies]] have found the discrepancy in male and female aggression to be more pronounced in childhood and the gender difference in adults to be modest when studied in an experimental context.<ref name=pmid3797558/> Still, there is evidence that males are quicker to aggression (Frey et al. 2003) and more likely than females to express their aggression physically.<ref>{{cite journal |doi=10.1002/1098-2337(1994)20:1<27::aid-ab2480200105>3.0.co;2-q |title=Sex differences in covert aggression among adults |journal=Aggressive Behavior |volume=20 |pages=27–33 |year=1994 |last1=Björkqvist |first1=Kaj |last2=Österman |first2=Karin |last3=Lagerspetz |first3=Kirsti M. J. |url=http://www.vasa.abo.fi/svf/up/articles/sexdiff_in_covert.pdf |citeseerx=10.1.1.453.7106 |access-date=6 December 2018 |archive-url=https://web.archive.org/web/20111203190129/http://www.vasa.abo.fi/svf/up/articles/sexdiff_in_covert.pdf |archive-date=3 December 2011 |url-status=dead  }}</ref> When considering indirect forms of non-violent aggression, such as [[relational aggression]] and [[social rejection]], some scientists argue that females can be quite aggressive, although female aggression is rarely expressed physically.<ref>{{cite journal |doi=10.1037/1089-2680.8.4.291 |title=Sex Differences in Aggression in Real-World Settings: A Meta-Analytic Review |journal=Review of General Psychology |volume=8 |issue=4 |pages=291–322 |year=2004 |last1=Archer |first1=John |s2cid=26394462 }}</ref><ref>{{cite journal |doi=10.1111/j.1467-8624.2008.01184.x |pmid=18826521 |title=Direct and Indirect Aggression During Childhood and Adolescence: A Meta-Analytic Review of Gender Differences, Intercorrelations, and Relations to Maladjustment |journal=Child Development |volume=79 |issue=5 |pages=1185–229 |year=2008 |last1=Card |first1=Noel A. |last2=Stucky |first2=Brian D. |last3=Sawalani |first3=Gita M. |last4=Little |first4=Todd D. |s2cid=7942628 }}</ref><ref>{{cite journal |doi=10.1891/vivi.2003.18.2.197 |pmid=12816404 |title=Gender Differences in Psychological, Physical, and Sexual Aggression Among College Students Using the Revised Conflict Tactics Scales |journal=Violence and Victims |volume=18 |issue=2 |pages=197–217 |year=2003 |last1=Hines |first1=Denise A. |last2=Saudino |first2=Kimberly J. |s2cid=28687366 }}</ref> An exception is [[intimate partner violence]] that occurs among couples who are engaged, married, or in some other form of intimate relationship.

Although females are less likely than males to initiate physical violence, they can express aggression by using a variety of non-physical means. Exactly which method women use to express aggression is something that varies from culture to culture. On [[Bellona Island]], a culture based on male dominance and physical [[violence]], women tend to get into conflicts with other women more frequently than with men. When in conflict with males, instead of using physical means, they make up songs mocking the man, which spread across the island and humiliate him. If a woman wanted to kill a man, she would either convince her male relatives to kill him or hire an assassin. Although these two methods involve physical violence, both are forms of indirect aggression, since the aggressor herself avoids getting directly involved or putting herself in immediate physical danger.<ref name="bjorkqvist">{{cite journal |doi=10.1007/BF01420988 |title=Sex differences in physical, verbal, and indirect aggression: A review of recent research |journal=Sex Roles |volume=30 |issue=3–4 |pages=177–88 |year=1994 |last1=Björkqvist |first1=Kaj |s2cid=142759440 }}</ref>

See also the sections on [[#Testosterone|testosterone]] and [[#Evolutionary explanations|evolutionary explanations]] for gender differences above.

===Situational factors===
{{See also|Stereotype threat}}

There has been some links between those prone to violence and their alcohol use. Those who are prone to violence and use alcohol are more likely to carry out violent acts.<ref>{{cite journal |doi=10.1002/ab.20231 |pmid=17922526 |title=Predictors of injurious assault committed during or after drinking alcohol: A case–control study of young offenders |journal=Aggressive Behavior |volume=34 |issue=2 |pages=167–74 |year=2008 |last1=Navis |first1=Charlene |last2=Brown |first2=Stephen L. |last3=Heim |first3=Derek }}</ref> Alcohol impairs judgment, making people much less cautious than they usually are (MacDonald et al. 1996). It also disrupts the way information is processed (Bushman 1993, 1997; Bushman & Cooper 1990).

Pain and discomfort also increase aggression. Even the simple act of placing one's hands in hot water can cause an aggressive response. Hot temperatures have been implicated as a factor in a number of studies. One study completed in the midst of the civil rights movement found that riots were more likely on hotter days than cooler ones (Carlsmith & Anderson 1979). Students were found to be more aggressive and irritable after taking a test in a hot classroom (Anderson et al. 1996, Rule, et al. 1987). Drivers in cars without air conditioning were also found to be more likely to honk their horns (Kenrick & MacFarlane 1986), which is used as a measure of aggression and has shown links to other factors such as generic symbols of aggression or the visibility of other drivers.<ref>{{cite journal |doi=10.1037/h0076960 |pmid=1142063 |title=Naturalistic studies of aggressive behavior: Aggressive stimuli, victim visibility, and horn honking |journal=Journal of Personality and Social Psychology |volume=31 |issue=6 |pages=1098–107 |year=1975 |last1=Turner |first1=Charles W. |last2=Layton |first2=John F. |last3=Simons |first3=Lynn S. |s2cid=36562997 }}</ref>

Frustration is another major cause of aggression.<ref name="pmid2667009">{{cite journal |vauthors=Berkowitz L |title=Frustration-aggression hypothesis: examination and reformulation |journal=Psychol Bull |volume=106 |issue=1 |pages=59–73 |date=July 1989 |pmid=2667009 |doi=10.1037/0033-2909.106.1.59 |url=}}</ref> The [[Frustration aggression theory]] states that aggression increases if a person feels that he or she is being blocked from achieving a goal (Aronson et al. 2005). One study found that the closeness to the goal makes a difference. The study examined people waiting in line and concluded that the 2nd person was more aggressive than the 12th one when someone cut in line (Harris 1974). Unexpected frustration may be another factor. In a separate study to demonstrate how unexpected frustration leads to increased aggression, Kulik & Brown (1979) selected a group of students as volunteers to make calls for charity donations. One group was told that the people they would call would be generous and the collection would be very successful. The other group was given no expectations. The group that expected success was more upset when no one was pledging than the group who did not expect success (everyone actually had horrible success). This research suggests that when an expectation does not materialize (successful collections), unexpected frustration arises which increases aggression.

There is some evidence to suggest that the presence of violent objects such as a gun can trigger aggression. In a study done by [[Leonard Berkowitz]] and Anthony Le Page (1967), college students were made angry and then left in the presence of a gun or badminton racket. They were then led to believe they were delivering electric shocks to another student, as in the [[Milgram experiment]]. Those who had been in the presence of the gun administered more shocks. It is possible that a violence-related stimulus increases the likelihood of aggressive cognitions by activating the [[semantic network]].

A new proposal links military experience to anger and aggression, developing aggressive reactions and investigating these effects on those possessing the traits of a serial killer. Castle and Hensley state, "The military provides the social context where servicemen learn aggression, violence, and murder."<ref>{{cite journal |doi=10.1177/0306624X02464007 |pmid=12150084 |title=Serial Killers with Military Experience: Applying Learning Theory to Serial Murder |journal=International Journal of Offender Therapy and Comparative Criminology |volume=46 |issue=4 |pages=453–65 |year=2002 |last1=Castle |first1=T. |last2=Hensley |first2=C |s2cid=35278358 }}</ref> [[Post-traumatic stress disorder]] (PTSD) is also a serious issue in the military, also believed to sometimes lead to aggression in soldiers who are suffering from what they witnessed in battle. They come back to the civilian world and may still be haunted by flashbacks and nightmares, causing severe stress. In addition, it has been claimed that in the rare minority who are claimed to be inclined toward serial killing, violent impulses may be reinforced and refined in war, possibly creating more effective murderers.<ref>{{cite journal|last1=blennow|last2=Manhem|date=20 January 2021|title=CSF studies in violent offenders|url=|journal=Journal of Neural Transmission|volume=108|pages=869–878|via=Forsman A.}}</ref>

===As a positive adaptation theory<!--linked from 'Non-aggression principle'-->===
Some recent scholarship has questioned traditional psychological conceptualizations of aggression as universally negative.<ref name="Ferguson & Beaver, 2009"/><ref>{{Cite web |last=Dolan |first=Eric W. |date=2023-09-30 |title=Contrary to popular belief, recent psychology findings suggest aggression isn't always tied to a lack of self-control |url=https://www.psypost.org/2023/09/contrary-to-popular-belief-new-psychology-paper-argues-aggression-isnt-always-tied-to-a-lack-of-self-control-213877 |access-date=2023-10-02 |website=PsyPost |language=en-US}}</ref> Most traditional psychological definitions of aggression focus on the harm to the recipient of the aggression, implying this is the intent of the aggressor; however this may not always be the case.<ref name="Smith, 2007">{{cite book |last=Smith |first=P. |year=2007 |chapter=Why has aggression been thought of as maladaptive? |chapter-url={{Google books|kfAdzNKaK5AC|page=65|plainurl=yes}} |title=Aggression and Adaptation: the Bright Side to Bad Behavior |pages=65–83 |publisher=Routledge |isbn=978-1-135-59375-9 }}</ref> From this alternate view, although the recipient may or may not be harmed, the perceived intent is to increase the status of the aggressor, not necessarily to harm the recipient.<ref name="Hawley & Vaughn, 2003">{{cite journal |doi=10.1353/mpq.2003.0012 |jstor=23096055 |title=Aggression and Adaptive Functioning: The Bright Side to Bad Behavior |journal=Merrill-Palmer Quarterly |volume=49 |issue=3 |pages=239–42 |year=2003 |last1=Hawley |first1=Patricia H. |last2=Vaughn |first2=Brian E. |s2cid=54998386 }}</ref> Such scholars contend that traditional definitions of aggression have no validity because of how challenging it is to study directly.<ref>{{Citation|last=Bjørkly|first=Stâl|title=Psychological Theories of Aggression: Principles and Application to Practice|url=http://dx.doi.org/10.1007/978-0-387-33965-8_2|work=Violence in Mental Health Settings|year=2006|pages=27–46|place=New York, NY|publisher=Springer New York|doi=10.1007/978-0-387-33965-8_2|isbn=978-0-387-33964-1|access-date=2021-05-05|url-access=subscription}}</ref>

From this view, rather than concepts such as assertiveness, aggression, violence and criminal violence existing as distinct constructs, they exist instead along a continuum with moderate levels of aggression being most adaptive.<ref name="Ferguson & Beaver, 2009"/> Such scholars do not consider this a trivial difference, noting that many traditional researchers' aggression measurements may measure outcomes lower down in the continuum, at levels which are adaptive, yet they generalize their findings to non-adaptive levels of aggression, thus losing precision.<ref name="Ferguson, 2010">{{cite journal |doi=10.1037/a0018941 |title=Blazing angels or resident evil? Can violent video games be a force for good? |journal=Review of General Psychology |volume=14 |issue=2 |pages=68–81 |year=2010 |last1=Ferguson |first1=Christopher J. |url=http://www.apa.org/pubs/journals/releases/gpr-14-2-68.pdf |citeseerx=10.1.1.360.3176 |s2cid=3053432 }}</ref>