AQA A2 Psychology Aggression Unit 3: The Role of Genetic Factors in Aggressive Behaviour Notes


A2 Psychology Aggression: The Role of Genetic Factors in Aggressive Behaviour Notes

What You Need to Know:

  • The role of genetic factors in aggressive behaviour

Selective breeding:

This involves choosing animals with aggressive characteristics and mating them with others to enhance this trait. This has a long history, e.g. Spanish fighting bulls and fighting *****.


  • Lagerspetz (1979) selectively bred mice to be 50% more aggressive than normal mice within 19 generations. They had heavier testes and forebrains and altered levels of neurochemicals, serotonin and noradrenaline.
  • Lagerspetz (1981) points out that genetic factors do not absolutely determine aggression since selectively bred aggressive mice can be conditioned to be less aggressive, and also aggressive wild animals can be tamed.

Twin Studies:

As selective breeding in humans is not possible, the next best thing is to study people with known genetic factors - i.e.twin studies, especially twins reared apart.

As humans are much more biologically complex and also live in more complex environments, discriminating between genetic and environmental influences on human aggression is very difficult.


  • A meta-analysis by Miles and Carey (1997) suggested heritability of 50% for aggression, but Plomin et al (1990) estimated a much smaller heritability.
  • Canter (1973) found a small correlation of 0.14 for MZs reared together, but O`Connor (1980) found a correlation of 0.72 for the same population.
  • This variability may be due to differences in methods of assessing aggression:

e.g. Rhee and Waldman (2002) found heritability estimate was


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