Contemporary study (option): McDermott et al. (2008)

Aim and sample

Aim: to see whether the MAOA gene leads people to behave aggressively, at a cost to themselves, when provoked.

Sample: 78 men, split by MAOA activity into MAOA-H (high activity) and MAOA-L (low activity) groups.

Procedure

• Participants earned money in a vocabulary task.
• In a 'power-to-take' game over four rounds, they believed an anonymous opponent (actually fictitious) took part of their earnings.
• Provocation was manipulated: high take (80%) or low take (20%).
• Aggression measure: participants could pay to make the opponent eat hot sauce, which the opponent was known to dislike. More hot sauce = more aggression.

Results

• High-take participants were aggressive more often and gave more hot sauce: overall 66% gave some hot sauce when 80% was taken, compared with 39% when 20% was taken.
• MAOA-L men were more aggressive than MAOA-H men.

MAOA difference significant at 80% taken, not at 20%

Maximum aggression, conclusions and evaluation

Conclusions: the more people are provoked, the more aggressive they are towards the person responsible; MAOA plays a role in aggression when there is provocation, so genes and environment interact.

Evaluation:

• Strengths: a behavioural measure of aggression (not self-report); controlled lab procedure that can be replicated; provocation was manipulated, so cause and effect for provocation can be judged.
• Weaknesses: all-male sample limits generalisation; giving hot sauce is artificial (low ecological validity); participants were deceived about the opponent; the gene groups were not manipulated, so other differences between them could matter.

MAOA difference significant in both conditions

Worked example

Overall, 66% gave some hot sauce when 80% was taken and 39% when 20% was taken. What does this show?

1. 66 - 39 = 27 percentage points more people aggressed under high provocation.
2. So greater provocation led to more aggression.
3. Combined with the MAOA differences, aggression depends on genes and environment together.

Answer: More provocation produced more aggression, and MAOA-L men reacted most: gene-environment interaction.

Check yourself

1. How many participants were in McDermott et al.?
   Show answer

   78 men. 78 male participants.

2. How was aggression measured?
   • The amount of hot sauce given to the opponent
   • A PET scan
   • Teacher ratings
   • A questionnaire about anger
   Show answer

   The amount of hot sauce given to the opponent. Hot sauce allocation was the behavioural measure.

3. How was provocation manipulated?
   • Participants were insulted
   • Participants watched violent films
   • The opponent took either 80% or 20% of the earnings
   • Some participants were given testosterone
   Show answer

   The opponent took either 80% or 20% of the earnings. High take versus low take.

4. At 80% taken, 44% of MAOA-L and 19% of MAOA-H men gave the maximum hot sauce. What is the difference?
   Show answer

   25 percentage points. 44 - 19 = 25 percentage points.

5. Overall 66% gave some hot sauce at 80% taken and 39% at 20% taken. What is the difference?
   Show answer

   27 percentage points. 66 - 39 = 27 percentage points.

6. Which is a conclusion of McDermott et al.?
   • Genes have no effect on aggression
   • MAOA plays a role in aggression when there is provocation
   • Women are more aggressive than men
   • Provocation reduces aggression
   Show answer

   MAOA plays a role in aggression when there is provocation. The gene predicted aggression, mainly when provoked.

7. Explain one weakness of McDermott et al. (2008).
   Show answer

   The sample was all male, so the findings cannot be generalised to women; also giving hot sauce in a lab game is artificial, so it may lack ecological validity.. Sample, task or ethics.

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Sources

• Pearson Edexcel International Advanced Subsidiary/Advanced Level in Psychology specification, Issue 5 (February 2021)
• Pearson IAL Psychology component guide: WPS02 (Issue 2, November 2024)
• Pearson IAL Psychology summary of studies: WPS02

Last updated 8 November 2026. Spotted a mistake? Tell us.