Evolutionary Psychology Lecture 9: Aggression.

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Evolutionary Psychology Lecture 9
Aggression.
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Learning Outcomes.

• At the end of this lecture you should be able to
  
• 1. Outline evolutionary explanations for the male
  propensity for increased aggression.
• 2. Discuss experimental and survey evidence for
  sex differences in aggression.

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Nature of Aggression.

• Wrangham Peterson (1996) point out that only
  humans and chimpanzees carry out the following
  aggressive actions
• Male-initiated territorial aggression.
• Groups of males raiding neighbouring territories.
• Lethal male/male group aggression.
• Traditional 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
• Long-recorded history of male aggression and
  warfare.
• Existence of higher levels of male aggression in
  all cultures.
• Existence of similar patterns of aggression in
  the chimpanzee.

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The Evolutionary Perspective.

• Evolutionary psychologists instead see aggression
  as a solution to particular adaptive problems and
  according to Buss Shackelford (1997) such
  problems are as follows
• 1). Coopting the resources of others Humans
  stockpile resources which are important for
  survival and reproduction.
• 2) 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.
• 3) Inflict costs on intrasexual rivals Same-sex
  rivals will compete for access to valuable
  resources that will attract females, or for
  females themselves.
• 4) 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.

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5. Deter Mates From Infidelity

• Aggression, or the threat of aggression may deter
  current partners from sexual infidelity.
• There is much evidence to suggest that male
  sexual jealousy is a key factor in spouse abuse.
• Daly Wilson (1988) argued that males will use
  violence and threats as strategies to limit their
  partners autonomy and so decrease the chance of
  infidelity.
• Spousal homicide is common, especially for women
  who
• Have left their partners.
• Have threatened to do so.
• Have been suspected of planning or actually
  committing adultery.
• Detroit (1972) 19 of homicide victims were
  related to the killer by marriage, compared to 6
  who were blood-relatives.
• Miami (1980) 10 of murder victims were marital
  relatives, compared to 2 of blood relatives.

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Relationship Status and Homicide Risk.
From Daly Wilson 1988, in Buss 1999 p58
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Homicide Rates in Marriage, Canada 1974-1983
Wives killed by husbands
Husbands killed by wives
From Daly Wilson 1988, p521.
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Contextual Factors.

• Wallace, (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.
• Another key factor is where the male lacks the
  necessary resources (ie unemployment).
• Women whose partners lose their jobs or fail to
  provide resources are more likely to have
  affairs.
• Almost half of the 1156 women murdered in New
  York between 1990-1994 were killed by husbands or
  boyfriends, and 67 of the crimes were committed
  in poor neighbourhoods with high rates of male
  unemployment (Belluck, 1997).

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Why are Males more Aggressive?

• One key aspect of aggression is the fact that
  males are much more likely than females to act as
  aggressors, e.g in Chicago between 1965-1980, 86
  of murders were committed by men, with 80 of the
  victims being other males (Daly Wilson, 1988).
• In 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
• They take more risks.
• They are more likely to choose immediate rewards.
  
• Males show aggressive behaviours from age 2
  onwards.
• Males are much more likely to escalate an
  altercation.
• Large sex differences favouring males are seen
  for aggressive fantasies, physical aggression,
  imitative aggression, and willingness to shock
  others (Hyde, 1986).
• Same-sex bullying involving direct physical
  aggression is more common in males (Ahmad
  Smith, 1994).

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Evolutionary Explanations.

• Evolutionary psychologists see aggression as an
  adaptive solution to sexual selection.
• Daly Wilson (1999) argue that due to
  inequalities in parental investment males have to
  compete with one another for access to the higher
  investing females.
• E.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).
• Human 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).

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1. Youth.

• Competition 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).
• Wilson Daly (1985) found that young males are
  more likely to engage in dangerous confrontations
  when the reward is a rise in social status.
• Young 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.
• This is referred to as the Young Male Syndrome'.
  
• In 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.

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Homicide Victims By Age.
From Buss, 1999 p 292
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2. Social Status.

• It is important for males to be able to initially
  achieve a certain social standing and then defend
  or improve it.
• Winners gain social status while their opponents
  lose social status.
• This is sensitive to social context -eg a man who
  beat up a child would lose more status than he
  gained.
• Males at the bottom of a social hierarchy face
  increased pressures to compete.
• We would predict that males who lack resources or
  social status would engage in correspondingly
  riskier behaviour to get what they want.
• Wilson Daly (1985) showed that males who were
  poor or unmarried were more likely to commit
  murder than were wealthier or married males.

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Step-Parents and Aggression.

• We would predict that substitute parents would
  care less for their adopted children than genetic
  parents.
• Children 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).
• Hill 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.
• A 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.

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Child Homicide Rate in Canada 1974-1983.
Natural parents
Step parents
From Daly Wilson, 1988 p 520
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Parent-Type and Abuse Rate
From Daly Wilson, 1985 p 202
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However..

• Temrin et al., (2000) analysed data from children
  aged 0-15 killed by their carers in Sweden
  between 1975-1995 (a total of 39 cases).
• They found that the percentage of children killed
  by their carers was as follows
• Two genetic parents 56.2
• One genetic parent 38.7
• One genetic and one non-genetic parent 5.1
• Two non-genetic parents 0.0

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Female Aggression.

• We 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).
• For 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.
• Females therefore have a greater tendency than
  males to protect their own lives and this will
  have enhanced their reproductive success.

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Female Behaviours Which Enhance Their
Reproductive Success.

• Females display more 'anxious' behaviour
  particularly with regards health and personal
  welfare issues.
• Certain phobias (animals, dangerous places) are
  more common in women.
• Women are less likely to engage in
  sensation-seeking behaviours.
• Women have lower rates of accidental injury.
• Women are less likely to take drugs.
• Women report higher levels of fear of crime.
• Women rate the importance of health higher than
  men, know more about health issues and are more
  likely to adopt preventative care.
• Women overestimate the dangers of a potential
  aggressive encounter.

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Female Aggression is an Adaptive Behaviour.

• Female aggression has traditionally been viewed
  as a gender-incongruent aberration.
• Campbell (1999) has however argued that certain
  aspects of female aggression are just as adaptive
  as certain kinds of male aggression.
• While 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.
• We 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).

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Female Aggression in Context.

• Women are significantly more likely to be
  attacked by another woman (generally an
  acquaintance) than a man.
• In 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).
• Normally 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.
• They are thus much more likely to form small
  co-operative groups (often with other female
  relatives). Evidence

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Group Behaviours.

• When placed into groups girls cooperate whilst
  boys compete.
• Girls who show strong competitive or dominance
  behaviours are rejected by their peer group.
• Boys use direct commands while girls use polite
  persuasion.
• Girls are very concerned to develop cohesion and
  shared norms within the group.
• Collaborative interchanges are more common in
  female groups while domineering exchanges are
  more common in male groups.
• Males are more likely to adopt an autocratic
  leadership role and accentuate differences
  between individuals and groups.

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Female Aggression is Indirect.

• Males are more likely to favour direct physical
  or verbal aggression.
• Such aggression would not be adaptive for
  females as they may get injured.
• Female aggression is therefore more likely to be
  'indirect', i.e. it takes the form of social
  manipulation where
• The 'attacker' may hide their identity by
  spreading nasty gossip.
• The individual may shun other members of the
  group or using their influence in the group to
  get other members ostracised.
• Girls are more likely to destroy an adversary's
  property or tell tales on them, use social
  ostracism and manipulation of others opinions.
• Female bullies are more likely to use indirect
  aggression rather than direct aggression.

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Female Criminal Behaviour is also Indirect

• Female 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).
• Where 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.
• Female-female homicide is very rare and women are
  much less likely to use weapons when aggressing.

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A Study of Female Aggression.

• According to Campbell et al., (1998),
  female-female aggression occurs most often in
  lower-class females aged 15-24 who generally know
  one another.
• The most frequent trigger for female-female
  aggression is competition for the attention of
  men and triggered by insults that slight the
  others sexual reputation.
• They analysed female-female assaults in
  Massachusetts during 1994 (482 in total) and
  found the following
• The majority of these cases were committed by
  females lt24 years old.
• The number of female-female assaults rose with
  increased dependency on welfare.
• Male unemployment was unrelated to female-female
  aggression.
• Women committed more property crime (fraud,
  shoplifting) and were more likely to engage in
  prostitution.