Genetics Explanations

Question 1

What are genetic factors?

Answer 1

The likelihood of behaving in a particular way is determined by a person’s genetic make-up

Question 2

Describe twin studies that support the genetic explanation of aggression

Answer 2

• Twin studies investigate aggression by comparing MZ and DZ twins, using the shared environment assumption, to see if MZ twins are more similar in aggressiveness than DZ twins and any differences must be explained by genes
• e.g. Coccaro et al concordance rate of 50% for MZ twins and 28% for DZ twins

Question 3

Describe adoption studies that support the genetic explanation of aggression

Answer 3

• Children raised in different families have been used to explore nature and nurture. If children are more similar to their biological parents, it’s a genetic influence, or if they’re more like adopted family, it’s a result of the environment.
• A study of over 14,000 adoptions in Denmark found that a significant number of adopted boys with criminal convictions had biological parents with convictions for criminal violence (Hutchings and Mednick)

Question 4

Describe a meta-analysis that supports the genetic explanations of aggression

Answer 4

• A meta-analysis by Rhee and Waldman combined the results of 51 twins and adoption studies and concluded that aggressive anti-social behaviour was largely a product of genetic contributions
• However, in this study, several variables, including the age of participants and assessment method for aggression, moderated the genetic influence on aggression

Question 5

Describe the role of the MAOA (and -L) gene in aggression

Answer 5

• MAOA gene controls the MAOA enzyme. This enzyme ‘catabolises’ (breaks down) serotonin in the synapse.
• MAOA-L (low activity variant of this gene) means there’s less catabolism and higher levels of serotonin

Question 6

Describe support for the role of the MAOA-L gene in aggression

Answer 6

• A study of a Dutch family found that many of its male members behaved in an aggressively manner, and a large proportion had been involved in violent crimes
• These men were found to have abnormal levels of MAOA in their bodies (Brunner et al)

Question 7

Describe the diathesis-stress model of aggression

Answer 7

The MAOA gene creates a genetic vulnerability to aggression and then the environment triggers aggression

Question 8

Describe support for the diathesis-stress model of aggression

Answer 8

• Caspi et al found high levels of aggression in those with the MAOA-L gene variant and had experiences significant trauma during the first 15 years of life
• Those with the MAOA-L gene but didn’t have early trauma experiences didn’t have high levels of aggression

Question 9

Give evaluation for the genetic explanation of aggression (supporting evidence)

Answer 9

• Tiihonen et al studied Finnish prisoners, revealing that the MAOA-L genotype in combination with another gene (CDH13 gene) was associated with extremely violent behaviour. There was no substantial evidence for either for these genes among non-violent offenders
• This suggests that this combination of genes is linked with aggression, providing validity to the genetic explanations for aggression

Question 10

Give evaluation for the genetic explanation of aggression (supporting evidence from sex differences in aggression)

Answer 10

• The MAOA gene is linked to the X chromosome and women have 2 X chromosomes while men only have 1.
• So when men inherit a X-linked gene, they’re more likely to be affected by it, while women inheriting the same gene are generally unaffected (as they have a second X chromosome with a ‘normal’ MAOA gene that prevents expression of the abnormal MAOA gene) This then explains Brunner’s findings, where it was only males in the family that were violent
• Therefore, this provides reliable explanation for why males typically show more aggression, supporting the genetic explanation of aggression

Question 11

Give evaluation for the genetic explanation of aggression (precise mechanism of the MAOA-serotonin-aggression link is unclear)

Answer 11

• Previous research linked low levels of serotonin to aggression (Duke et al). But, the MAOA-L gene causes low activity of the MAOA enzyme leading to higher serotonin levels, as the low-activity enzyme doesn’t catabolise serotonin.
• This shows that the relationship between the MAOA gene, serotonin and aggression isn’t yet fully understood. Therefore, the genetic explanation isn’t a comprehensive explanation for aggression

Question 12

Give evaluation for the genetic explanation of aggression (difficulties in establishing the genetic contributions to aggression)

Answer 12

• e.g. more than 1 gene usually contributes to a certain behaviour, or there are non-genetic influences (environmental) on the manifestation of aggression. Furthermore, these factors may interreact, so genetic factors may affect which environmental factors have an influence
• Therefore, taking a biological reductionist view oversimplifies aggression as it’s a complex behaviour with multiple genetic and non-genetic factors involved