The use of twin studies to investigate genetic relatedness and aggression.
List A from Social Psychology
A twin study investigates nature and nurture by comparing identical (MZ) and non-identical(DZ) twins.
Monozygotic (MZ) twins are genetically identical. They split from the same egg shortly after conception. They share 100% of their genes and (because of this) will always be the same sex. They probably look identical too.
Dizygotic (DZ) twins are non-identical. They developed from separate eggs, just like any pair of siblings, but at the same time. They are just like any brother or sister, except that they are born at the same time. Same-sex DZ twins may share up to 50% of their genes and may look identical (but don’t have to). DZ twins may be mixed-sex and don’t have to be any more similar than any other set of brothers and sisters.
Twin studies are measured using concordance rates, which are usually expressed as a percentage. 100% means that all twins have a behaviour in common and 0% means that no twins have a behaviour in common. Psychologists compared concordance rates of MZ twins and DZ twins to determine the extent to which a behaviour is a result of nature (genetics) and nurture (environment).
We can be sure of this because both sets of twins share the same home life and upbringing: it’s only their genetic similarity that sets them apart from each other.
You could gain a sample of monozygotic twin pairs and same-sex dizygotic twin pairs, where one of the twins would have been in trouble for aggression. You could check the finger prints and blood type of each twin pair to determine whether they were monozygotic or dizygotic. You would then see how many of the second twins in each pair had also been in trouble for aggression. You could operationalise being in trouble for aggression by the number of times each participant had been arrested for fighting.
Mz Concordance Rate Is 100% = Behaviour is entirely genetic
Mz Concordance Rate Is Significantly Less Than 100% = Behaviour is partly the result the of environment
Mz Concordance Rate Is Similar To Dz = Concordance Rate Behaviour is partly attributed to the environment (nurture)
Mz Concordance Rate Is Significantly Higher Than Dz = Concordance Rate Behaviour is partly attributed to nature (genetics)
Monozygotic twins tend to be brought up in the same environment and have shared the same pre-natal environment, therefore it is hard to determine whether aggression is genetic or due to the same environment.
The predisposition of aggression is not 100% twin studies are not able provide conclusive evidence of genetic influences on human behaviour.
Twin studies have small sample sizes as twins are not common, so findings may not be representative of a wider population.
Identify which sample of twins has a higher genetic relatedness between aggression and antisocial behaviour. (1) June 2016
Explain one strength and one weakness of the twin study method. (4) June 2016
Vanessa researched genetic relatedness and aggression. She used a twin study to determine if aggression was linked to genes. Describe how Vanessa might have carried out a twin study to investigate genetic relatedness and aggression. (4) January 2019
Explain one weakness of using twin studies to investigate genetic relatedness. (2) January 2019