The role of Genes
Coccaro et al (1997) found that in adult twin pairs, nearly 50% of the variance in direct aggressive behaviour could be attributed to genetic factors.
Brunner et al (1993) studied a dutch family whose malemembers had a history of violence such as **** and arson,and found they had a defective gene to control MAOA production- so aggression hormones were very high.
(MAOA regulates the production of other hormones involved in aggression)
Hutchings and Mednick (1975) studied 14,000 boys who had been adopted in denmark, and found that a substantial number of boys with criminal convictions also had biological parents (notably fathers) with criminal convictions.
Hodgkinson et al (1985) found that trainee nurses were more likely to suffer violent assault than experienced nurses
Allan and Madden (2008) studied over 11,000 students involved in clubs and teams in the US and found that over half had experienced hazing.
McCorkle et al (1995) found that overcrowding, lack of privacy and meaningful acitvity all influence violence.
Nijman et al (1999) found that increased personal space failed to decrease thelevel of violent incidents among patients
Social Learning Theory
Bandura (1961) Bobo doll study- children were put into two groups and watched either a model acting aggressively (both physically hitting, and verbal violence such as saying 'POW') towards a bobo doll, or a model acting non-aggressively towards a bobo doll. The children were then shown attractive toys that they couldnt play with, to raise their frustration levels, and then placed in a room with a bobo doll, amongst other toys. Those children exposed to an aggressive model all replicated the violence, and most replicated the verbal aggression. Boys were more violent towards it, but there was no difference between the girls and the boys in terms of verbal aggression. Those in the non-violent group exhibited virtually no violence.
Bandura (1961) conducted another version of the bobo doll study, where children were split into three groups, and each watched a model behaving aggressively to a bobo doll, but there were three endings- a) the model being rewarded for their behaviour, b) the model being punished, and c) the model recieving no consequence. The children who observed a) exhibited the most violence, the children who observed b) exhibited the least, and those who observed c) exhibited violence levels between the two.
Zimbardo (1969) - had groups of four females, in one of two conditions, a) deindividuated, or b) individuated. In a), they wore bulky lab coats, hoods that hid their faces, and were never referred to by name. In b), they wore normal clothes, were introduced by name, and wore large name tags. They then had to shock the 'learner' as part of a learning aid- those in the deindividuated condition shocked for twice as long as those in the individuated condition.
Mullen (1986) analysed newspaper cuttings of lynchings that took place in the US between 1899 and 1946, and found that the larger the mob, the more savagery in which they killed their victims.
Johnson and Downing (1979) same as Zimbardos method of experiment with the shocking, but this time half wore masks and overalls, and the other half wore nurses uniforms. Those wearing masks and uniforms shocked more than control, and those wearing nurses uniforms shocked less than the control.
Neural and Hormonal factors in aggression
Mann et al (1990) gave 35 healthy participants dexfenfluramine, which depletes serotonin. The participants were tested before and after with a hostility and aggression questionnaire: male participants scores rose ( but females didnt.)
Raleigh (1991) studied aggression in vervet monkeys. Two groups of monkeys- a) fed on high tryptophan diets, b) fed on low tryptophan diets. Tryptophan increases serotonin- the monkeys in condition b) exhibited higher aggression levels because of decreased serotonin.
Buitelaar (2003) found that the use of antipsychotics that reduce dopamine reduced the aggressive behaviour in delinquents.
Dabbs et al (1987) measured salivary testosterone in criminals. Those with a the highest testosterone had a history of primarily violent crime, and those with the lowest had a history of non-violent crime.
McBurnett et al (2000) studied boys with behavioural problems over four years. Those with the lowest cortisol exhibited 3 times the aggressive symptoms, and began anti-social acts earlier than those with higher or fluctuating cortisol levels.
Evolutionary explanation of aggression
Wilson et al (1995) found that women who agreed with questionnaire items such as 'he is jealous and doesnt want you to talk with other men' were twice as likely to have experienced serious violence from their partners. 72% needed medical attention after a violent assault from their partners.
Daly and Wilson (1988) suggested that death of their partner was an unintended outcome of an adapted mechanism designed to control their partner, not kill them.,
Daly and Wilson (1985) studied homicides in detroit- 43% of male victimsand 41% of male perpetratorswere unemployed, despite the fact that only 11% of males were unemployed that year.
Group display as an adaptive response
Myrdal (1944) suggests that lynch mobs are caused by a fear of the *****.
Patterson (1999) suggests that lynch mobs were more active during that time due to it being a time of major social transition after the collapse of slavery.
Ridley (1997) when groups feel at risk, survival of the group is important- cooperative group defence and antagonism to outsiders goes hand in hand.
Shaw and Wong (1989) mechanisms that prompt suspicion towards outsiders would have been favoured by natural selection- our ancestors would have been able to avoid attack, and so leave behind more offspring.
Foldesi (1996) studied xenophobia in sports events. He said that the racist core of extremists led to an increase in spectator violence in general, xenophobic outbursts in particular. Gypsies, Jews and Russians were the usual targets of the violence.