Genetics

It is questionable whether biological factors; such as the role of genetics, are sufficient in themselves to explain human aggression. 

Sandberg argued that aggression in males is caused by their Y chromosomes (XY), which women do not have. As men show more aggression than women, and carry the Y chromosome, it is assumed that carrying another Y chromosome would cause increased aggression. Called the XYY gene, this has been shown in many men. This may be cause men with the XYY gene produce higher levels of testosterone, which is known to cause aggression. 

Bruner identified a faulty gene on the X chromosome of men, called the MAOA-L gene. The MAOA gene produces Monoamine Oxidase A, an enzyme that regulates neurotransmitters such as a serotonin, which have a role in aggressive behavior. The faulty MAOA-L gene ('L' stands for low activating) produced lower levels of Monoamine Oxidase A, which causes an imbalance in the neurotransmitter responsible for aggression. 

Goldman identified a faulty gene in men, known as Q20*. This influences the way in which neurons use serotonin, which is likely to cause aggression.

Strong evidence to support the role of genetic factors in aggression comes from Hutchings and Mednick in a study of 14,000 Danish adoptions, who found a strong correlation between parental aggression and juvenile violent crime, even though the children had been reared apart from their biological parents. This suggests that aggression is caused by genetic factors as pro-aggressive personalities must be inherited. 

Convincing evidence suggest the sufficiency of genetic factors comes from Miles and Carey, who performed meta-analysis and found that Mz twins who were raised apart showed a +0.64 correlation in aggression showing that genetic factors have a strong influence in aggression as no environmental factors are present, however, undermining genetic factors being self sufficient is that Mz twins who lived together showed a stronger correlation of +0.72 suggesting that environmental conditions contribute to genetics.

Questionable evidence comes from Goldman, who found that male aggressive prisoners were tree times more likely to carry the faulty Q20* gene compared to a control group. However, undermining this is that there is difficulty establishing cause and effect because it is impossible to establish a causal relationship there is no direct control over the independent variable, as all prisoners committed the crime when drunk.

Some evidence for genetic factors comes from Cases, who disabled the X chromosome in male and female mice and found no effect on the female mice but more male mice because more aggressive, showing that men who are XYY are more aggressive. However, this has low internal validity  because it doesn’t measure what it intends as it measure the effect of the Y chromosome, but not the XYY chromosomes. Also it can be criticised for low external validity, which is the extent to which it can be generalised, however, due to the use of mice it cannot be generalised to humans. Finally, undermining genetic factors is that this research can be criticised for difficulty in operationalisation, this is because all people will consider different behaviours as aggressive in mice.

Being from the Biological Approach, a strength of genetic explanations of aggression is that they are culturally absolute because they apply equally to all cultures. This is because all humans are likely to share a similar genetic makeup in aggression.

However, other psychologists argue that genetic explanations of aggression can be criticised for being Eurocentric because research to support them is mainly conducted in Europe or North America (where complex genetic techniques are more affordable) and then unfairly applied to all cultures. 

Genetic explanations of aggression may also be criticised for being constrained because they limit our free will in suggesting that we are genetically motivated to show aggression, over which we have no control. This ignores evidence to suggest that we can control our biological urge to show aggression (as shown by entirely non-aggressive communities, such as the Amish). 

Furthermore, the genetic explanations of aggression can be criticised for being simplistic because they ignore other important influences in aggression. For example, they ignore the role played by environmental learning, as seen in Bandura's Bobo Doll study. Moreover, research by Berkowitz and LaPage suggests the importance of cue arousal, which suggests a cue is necessary to spark an aggressive act, even if we have a biological pre-disposition for aggression. 

For this reason, genetic explanations of aggression can be criticised for ignoring the role of nurture in the nature-nurture debate. This is unrealistic because most psychologists recognise the interaction of both sides of the debate, in the nurture of nature (Robert Plomin).

Therefore, it is unlikely that genetic factors are sufficient explanation of human aggression as other factors (e.g. SLT, Bandura) must also be involved in the development of pro-aggressive personalities.