Another weakness of the theory is that it is deterministic. This means that it assumes that every XYY male will be aggressive. For example, since this time, it has been shown that males with this gene aren’t aggressive if they choose not to be (it should also be noted recent research shows that the gene isn’t strongly linked to aggression). This is a problem because it ignores the human characteristic of free will.
Evidence to support the role of genes in aggressive behaviour comes from Lagerspetz. He bred 25 generations of mice, choosing the most aggressive to breed together and the least aggressive to breed together. The result was on group of very aggressive mice and one group of highly docile mice. This supports the theory as it appears that the mice inherited either aggressive or non-aggressive genes from their parents.
One problem with this research is that it used extrapolation. This means that it attempts to learn about human physiology (genes) from experimentation on mice. For example, humans are more psychologically and physiologically complex (probably) than mice, so we may have other reasons for aggression. This is a problem because the research cannot be generalised to humans.
Neural Mechanisms
One biological explanation of aggression involves neurotransmitters. These are chemicals that allow impulses to be transmitted around the brain. The neurotransmitter Serotonin has been thought to reduce aggression by inhibiting responses to emotional stimuli. Low levels have been linked with impulsive behaviour and aggression. For example, some recreational drugs that lower serotonin levels cause aggressive behaviour. Additionally, domestic pets have been found to produce more serotonin than their wild counterparts. Furthermore, increases in dopamine activity via the use of amphetamines have been linked with aggression, while Buitelaar found that antipsychotics which reduce dopamine activity also lower aggression levels in violent delinquents.
Neural explanations of aggression can be criticised for ignoring the behavioural approach. This means that by focusing solely on biology (neurotransmitters) the theory ignores the role learning may play on aggression. For example, Bandura demonstrated children learned through Social Learning Theory to be aggressive towards a Bobo Doll after observing an adult being aggressive. This is a problem because it suggests that learning also plays a role in aggression, so a purely biological approach may be too narrow.
Another weakness of neural explanations of aggression is that they are reductionist. This means that they take a complex behaviour (aggression) and reduce it down to its basic parts (neurotransmitters). For example, the explanations do not take into account external factors, such as institutionalisation, which research has shown to increase aggression levels. This is a problem because although focusing solely on neurotransmitters makes the theory more measurable, it could be ignoring other important factors, making the theory too simplistic.
Evidence to support neural explanations of aggression comes from Raleigh et al. They found that vervet monkies fed on a diet high in tryptophan (which increased serotonin levels) demonstrated lower levels of aggression than ose fed on a diet low in tryptophan. They concluded the tryptophan decreases aggression. This supports the theory as it appears that the serotonin levels raised by the tryptophan reduced aggression.
One weakness of this research is that it used extrapolation. This means that it tries to learn about human physiology from experimentation on animals (vervet monkeys in this case). For example, humans are physiologically different than monkeys and may have reacted differently to a high tryptophan diet. This is a problem because it means that the research cannot be generalised to humans.
Hormonal Mechanisms
One biological explanation of aggression involves hormonal mechanisms. Since the 1980s in the UK, there have been a number of high profile cases in which a woman had a murder charge reduced to manslaughter after hormonal fluctuations caused by Pre Menstrual Tension (PMT) were taken into account. The lawyers acting for such women state that their clients were acting as ‘automatons’ of their hormones i.e. they became aggressive due to their hormones, most notably higher testosterone levels. Testosterone is an androgen produced by the Leydig cells in the adrenal cortex and male testes. Males produce about ten times more than females and it has been linked with aggression. Its release follows a circadian rhythm. The ‘Basal Model of Testosterone’ suggests that the more testosterone is released, the more competitive and dominant the person will become. This may result in increased aggression levels, or even, as stated above, murder.
One weakness of the ‘Basal Model of Testosterone’ is that it ignores the behavioural approach. This means that by focusing solely on biology (hormones) the model ignores the role learning may play on aggression. For example, Bandura demonstrated children learned through Social Learning Theory to be aggressive towards a Bobo Doll after observing an adult being aggressive. This is a problem because it suggests that learning also plays a role in aggression, so a purely biological approach may be too narrow.
Another weakness of the model is that it is deterministic. This means that it assumes that all women will act aggressively when they experience the hormone shifts that accompany PMT. This is misleading because many women, for example, do not exhibit any aggressive behaviour if they choose not to, even if they feel aggressive. This is a problem because the model ignores the human characteristic of free will.
Evidence to support the ‘Basal Model of Testosterone’ comes from Dabbs et al. They measured salivary testosterone levels of violent and non-violent criminals. A correlation between testosterone levels and number of aggressive crimes committed was found. This supports the model by suggesting that the high levels of testosterone caused the criminals to exhibit more aggressive behaviour.
One weakness of this research is that it only correlational. This means that only a link between testosterone levels and the number of aggressive crimes committed can be established. For example, other factors (extraneous variables) may have caused the correlation, such as a subjective opinion as what counts as an ‘aggressive’ crime. This is problematic as it means that a cause and effect relationship cannot be established between the two variables.