Transcript EVOLUTIONARY PSYCHOLOGY, SESSION 6: MALE MATE …

Evolutionary Psychology Lecture 9:
Aggression.
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.
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.
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.
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 bloodrelatives.
 Miami (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 1974-1983
Wives killed by husbands
Husbands killed by wives
From Daly & Wilson 1988, p521.
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).
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).
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).
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.
Homicide Victims By Age.
From Buss, 1999 p 292
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.
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.
Child Homicide Rate in
Canada 1974-1983.
Natural
parents
From Daly & Wilson, 1988 p 520
Step parents
Parent-Type and Abuse Rate
From Daly & Wilson, 1985 p 202
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%
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 infant’s 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.
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.
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).
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:
Group Behaviours.
 When placed into group’s 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.
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.
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.
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
<24 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.