Presentation on theme: "Evolutionary Psychology Lecture 9: Aggression.. Learning Outcomes. zAt the end of this lecture you should be able to: z1. Outline evolutionary explanations."— Presentation transcript:
Evolutionary Psychology Lecture 9: Aggression.
Learning Outcomes. zAt the end of this lecture you should be able to: z1. Outline evolutionary explanations for the male propensity for increased aggression. z2. Discuss experimental and survey evidence for sex differences in aggression.
Nature of Aggression. zWrangham & Peterson (1996) point out that only humans and chimpanzees carry out the following aggressive actions: zMale-initiated territorial aggression. zGroups of males raiding neighbouring territories. zLethal male/male group aggression. zTraditional psychological theories explain aggression as being caused by cultural factors such as observation and imitation via the influence of TV, increased alienation, and social crowding. However such explanations do not explain: zLong-recorded history of male aggression and warfare. zExistence of higher levels of male aggression in all cultures. zExistence of similar patterns of aggression in the chimpanzee.
The Evolutionary Perspective. zEvolutionary psychologists instead see aggression as a solution to particular adaptive problems and according to Buss & Shackelford (1997) such problems are as follows: z1). Coopting the resources of others: Humans stockpile resources which are important for survival and reproduction. z2) Defence against attack: The presence of individuals who may attack you prompts groups or individuals to use aggression as a means of preventing ones resources from being taken. z3) Inflict costs on intrasexual rivals: Same-sex rivals will compete for access to valuable resources that will attract females, or for females themselves. z4) Negotiate status hierarchies: Aggression can enhance ones personal status within a group, in Western cultures aggression has been ritualised within sporting contexts and top performers can achieve very high status.
5. Deter Mates From Infidelity zAggression, or the threat of aggression may deter current partners from sexual infidelity. zThere is much evidence to suggest that male sexual jealousy is a key factor in spouse abuse. zDaly & Wilson (1988) argued that males will use violence and threats as strategies to limit their partners autonomy and so decrease the chance of infidelity. zSpousal homicide is common, especially for women who: zHave left their partners. zHave threatened to do so. zHave been suspected of planning or actually committing adultery. zDetroit (1972): 19% of homicide victims were related to the killer by marriage, compared to 6% who were blood- relatives. zMiami (1980): 10% of murder victims were marital relatives, compared to 2% of blood relatives.
Relationship Status and Homicide Risk. From Daly & Wilson 1988, in Buss 1999 p58
Homicide Rates in Marriage, Canada Wives killed by husbands Husbands killed by wives From Daly & Wilson 1988, p521.
Contextual Factors. zWallace, (1986) found that recently estranged wives were at a very high risk of being murdered by their former husbands particularly if they were young or very attractive. zAnother key factor is where the male lacks the necessary resources (ie unemployment). zWomen whose partners lose their jobs or fail to provide resources are more likely to have affairs. zAlmost half of the 1156 women murdered in New York between were killed by husbands or boyfriends, and 67% of the crimes were committed in poor neighbourhoods with high rates of male unemployment (Belluck, 1997).
Why are Males more Aggressive? zOne key aspect of aggression is the fact that males are much more likely than females to act as aggressors, e.g in Chicago between , 86% of murders were committed by men, with 80% of the victims being other males (Daly & Wilson, 1988). zIn all known cultures males commit more murders and are more likely to be the victim of assault than are females. If extreme violence is ignored, males still show the following: zThey take more risks. zThey are more likely to choose immediate rewards. zMales show aggressive behaviours from age 2 onwards. zMales are much more likely to escalate an altercation. zLarge sex differences favouring males are seen for aggressive fantasies, physical aggression, imitative aggression, and willingness to shock others (Hyde, 1986). zSame-sex bullying involving direct physical aggression is more common in males (Ahmad & Smith, 1994).
Evolutionary Explanations. zEvolutionary psychologists see aggression as an adaptive solution to sexual selection. zDaly & Wilson (1999) argue that due to inequalities in parental investment males have to compete with one another for access to the higher investing females. zE.g male elephant seals are much larger than females and much aggressive as they defend a harem of females. A small number (around 5%) of successful dominant males will sire 85% of all offspring in a breeding season (Le Boeuf & Reiter, 1988). zHuman males are the product of ancestral males who had to engage in risky strategies of intrasexual competition for access to the higher investing females, males die on average around 7 years younger than females (Trivers, 1985).
1. Youth. zCompetition amongst males is highest in those entering the breeding market as they have to gain status to enable them to compete against other males (older and higher status). zWilson & Daly (1985) found that young males are more likely to engage in dangerous confrontations when the reward is a rise in social status. zYoung males are also more likely to escalate trivial altercations when there is potential 'loss of face' in front of other competing males or potential female partners. zThis is referred to as the Young Male Syndrome'. zIn adolescence the killing of males drastically increases, reaching a peak in the early 20's, by this age males are 6 times more likely to be murdered by other young males.
Homicide Victims By Age. From Buss, 1999 p 292
2. Social Status. zIt is important for males to be able to initially achieve a certain social standing and then defend or improve it. zWinners gain social status while their opponents lose social status. zThis is sensitive to social context -eg a man who beat up a child would lose more status than he gained. zMales at the bottom of a social hierarchy face increased pressures to compete. zWe would predict that males who lack resources or social status would engage in correspondingly riskier behaviour to get what they want. zWilson & Daly (1985) showed that males who were poor or unmarried were more likely to commit murder than were wealthier or married males.
Step-Parents and Aggression. zWe would predict that substitute parents would care less for their adopted children than genetic parents. zChildren of homes involving a step-parent (especially a father) are 40 times more likely to appear in abuse statistics, juvenile crime statistics, or to run away from home (Daly & Wilson, 1985). zHill & Kaplan (1988): found that in the Ache Indians, out of 67 children raised by mother and stepfather, 43% had died before age 15 compared with 19% of children raised by their genetic parents. zA survey in the USA (1976) revealed that a step-child was 100 times more likely to be fatally abused than a same-age child living with genetic parents. The children most at risk are those aged 0-5.
Child Homicide Rate in Canada Natural parents Step parents From Daly & Wilson, 1988 p 520
Parent-Type and Abuse Rate From Daly & Wilson, 1985 p 202
However.. zTemrin et al., (2000) analysed data from children aged 0-15 killed by their carers in Sweden between (a total of 39 cases). zThey found that the percentage of children killed by their carers was as follows: zTwo genetic parents = 56.2% zOne genetic parent = 38.7% zOne genetic and one non-genetic parent = 5.1% zTwo non-genetic parents = 0.0%
Female Aggression. zWe would perhaps expect that females would be much less violent than men as they face the brunt of childrearing and so the survival of the mother is of major importance to the well-being of the child (particularly in infancy). zFor example in the Ache Indians of Paraguay if the mother dies in the first year of the infants life, the subsequent infant mortality rate is 100%. zFemales therefore have a greater tendency than males to protect their own lives and this will have enhanced their reproductive success.
Female Behaviours Which Enhance Their Reproductive Success. zFemales display more 'anxious' behaviour particularly with regards health and personal welfare issues. zCertain phobias (animals, dangerous places) are more common in women. zWomen are less likely to engage in sensation-seeking behaviours. zWomen have lower rates of accidental injury. zWomen are less likely to take drugs. zWomen report higher levels of fear of crime. zWomen rate the importance of health higher than men, know more about health issues and are more likely to adopt preventative care. zWomen overestimate the dangers of a potential aggressive encounter.
Female Aggression is an Adaptive Behaviour. zFemale aggression has traditionally been viewed as a gender-incongruent aberration. zCampbell (1999) has however argued that certain aspects of female aggression are just as adaptive as certain kinds of male aggression. zWhile males compete with one another for dominance and its rewards, females compete with one another for resources (i.e. other males) which can directly enhance their reproductive success. zWe would thus expect the severity of competition to be related to the availability of resource-rich males, where males are few or are of poor quality then female competition and aggression should be higher (Campbell, 2001).
Female Aggression in Context. zWomen are significantly more likely to be attacked by another woman (generally an acquaintance) than a man. zIn the USA, Campbell et al., (1998) found that out of 297 female-female fights, 121 were concerned with men and 67 were about subsistence concerns (food, money, domestic goods etc). zNormally though, the fear of direct physical assault means that females are less likely to form dominance hierarchies which would entail direct physical aggression to develop and maintain. zThey are thus much more likely to form small co-operative groups (often with other female relatives). Evidence:
Group Behaviours. zWhen placed into groups girls cooperate whilst boys compete. zGirls who show strong competitive or dominance behaviours are rejected by their peer group. zBoys use direct commands while girls use polite persuasion. zGirls are very concerned to develop cohesion and shared norms within the group. zCollaborative interchanges are more common in female groups while domineering exchanges are more common in male groups. zMales are more likely to adopt an autocratic leadership role and accentuate differences between individuals and groups.
Female Aggression is Indirect. zMales are more likely to favour direct physical or verbal aggression. zSuch aggression would not be adaptive for females as they may get injured. zFemale aggression is therefore more likely to be 'indirect', i.e. it takes the form of social manipulation where: zThe 'attacker' may hide their identity by spreading nasty gossip. zThe individual may shun other members of the group or using their influence in the group to get other members ostracised. zGirls are more likely to destroy an adversary's property or tell tales on them, use social ostracism and manipulation of others opinions. zFemale bullies are more likely to use indirect aggression rather than direct aggression.
Female Criminal Behaviour is also Indirect zFemale criminal behaviour comes close to that of males only in larceny/theft, particularly where direct confrontations are absent (i.e. credit card fraud as opposed to mugging). zWhere female-female physical violence does occur, it is most often triggered by competition over scarce resources (usually men) and is most common between current wife/girlfriend and ex wife/girlfriend. zFemale-female homicide is very rare and women are much less likely to use weapons when aggressing.
A Study of Female Aggression. zAccording to Campbell et al., (1998), female-female aggression occurs most often in lower-class females aged who generally know one another. zThe most frequent trigger for female-female aggression is competition for the attention of men and triggered by insults that slight the others sexual reputation. zThey analysed female-female assaults in Massachusetts during 1994 (482 in total) and found the following: zThe majority of these cases were committed by females <24 years old. zThe number of female-female assaults rose with increased dependency on welfare. zMale unemployment was unrelated to female-female aggression. zWomen committed more property crime (fraud, shoplifting) and were more likely to engage in prostitution.