Genetic Factors in Aggression

Question 1

Which chromosome is the genetic cause of aggression found on?

Answer 1

Y

Question 2

What do twin studies show?

Answer 2

Heritability

Question 3

What is the concordance rate for MZ and DZ twins for verbal aggression?

Answer 3

MZ 28%
DZ 7%

Question 4

What is the concordance rate for physical aggression in MZ and DZ twins?

Answer 4

MZ 50%
DZ 19%

Question 5

What are adoption studies used for?

Answer 5

Adoption studies look to see whether environmental influences operate by comparing adopted child with their adoptive parents

Question 6

What percentage did Rhee and Waldman find for genetic influences accounting for variance in aggression from meta analysis of studies into direct aggression and anti social behaviour?

Answer 6

41%

Question 7

What does the MAOA gene do?

Answer 7

Control production of the MAO-A enzyme which is responsible for regulating serotonin.

Question 8

What does the L in MAOA L mean?

Answer 8

Low activity variant

Question 9

What does the MAOA L gene do?

Answer 9

Produces the low activity version of the MAO-A enzyme. This means serotonin cannot be controlled as well leading to increased aggression.

Question 10

How does the high activity variant of the MAOA gene affect aggression?

Answer 10

Lower levels of aggression

Question 11

What did Brunner find about the cause of aggression in a family of 28 dutch men who were involved in aggressive, violent crime?

Answer 11

All men had abnormally low levels of the MAO-A enzyme and MAOA L gene

Question 12

Describe how diathesis stress affects aggression when a person has the MAOA L gene.

Answer 12

Research has found that the low activity variant of the MAOA-L gene is caused when the person as experienced significant childhood trauma during the 1st 15 years of life. Those who possessed the MAOA-L gene but did not have childhood trauma showed lower levels of aggression.

Question 13

Evaluate the statement: ‘The MAOA-L gene is only related to adult aggression when combined with early traumatic experience.’
What did Frazzetto find an association between in his research? (diathesis stress)
Does this support diathesis stress or not?

Answer 13

For example, Frazzetto found an association between higher levels of anti social aggression and the MAOA-L gene in men as expected. But this was only the case in those who had experienced significant trauma during the 1st 15 years of life. Those who didn’t have trauma did not have high levels of aggression as adults, even if they possessed the MAOA-L variant. This shows strong evidence for diathesis stress and how it leads to aggression.

Question 14

Explain the limitation of twin studies lacking validity.
What do most twins share aside from genetics? What is this assumption called?
Why might DZ twins not share this to the same extent of MZ twins?
Why might this assumption be wrong?
What does this suggest about the accuracy of concordance rates?

Answer 14

In every pair of twins, both individuals share the same environment as eachother. However, DZ twins may not share the same environment to the same extent that MZ twins do, yet we assume that they do and this is called the equal environments assumption. But the assumption may be wrong because one aspect of the environment is the way twins are treated by others. MZ twins are treated very similarly by parents (ie praise for being equally aggressive) but DZs are treated in less similar ways. This means that concordance rates are inflated and genetic influences on aggression may not be as great as twin studies suggest.

Question 15

Explain the limitation of the genetic explanation being reductionist.
What is the cause of aggression reduced down to?
On one hand, what are the benefits of reductionism?
On the other hand, what might a biologically reductionist theory ignore?
For example, give the level that aggression caused by SLT is explained at.
Why is the genetic explanation of aggression parsimonious?

Answer 15

This is because it simplifies the cause of aggression to be because of the Y chromosome and MAOA-L gene variant. On one hand, this is a strength because we can scientifically test and treat aggression as we know there is an underlying biological cause that can be addressed with biological therapies (such as serotonin based drugs). However, this type of reductionism is a limitation because we ignore other factors that can cause aggression (such as psychological). For example, in SLT, we consider the idea that aggression is learnt and explained at a higher socio/cultural explanation. Therefore, to gain a complete understanding of aggression we should not only look at the parsimonious biological explanation.

Question 16

Explain the limitation that the precise mechanism for MAOA serotonin aggression is unclear.
If MAOA L causes low activity of the MAO-A enzyme, what would be expect serotonin levels to actually be?
Therefore, what might it be more accurate to suggest about serotonin levels and the cause of aggression?
What does this tell us about our actual understanding of aggression, MAOA and serotonin?

Answer 16

Research has linked aggression with low levels of serotonin. But the MAOA-L gene causes low activity of the MAO-A enzyme which in turn should lead to high serotonin in synapses. In people with the MAOA-L variant, it may be more accurate to say that their serotonin levels are disrupted rather than lower or higher than normal. This shows that the relationship between MAOA. Serotonin and aggression is not fully understood.