The Two Headed Boy

Francis Galton conducted some of the first twin studies and was the first to publish research that used the expression nature versus nurture.

You can read an article about the basic twin study method and how twin studies try to identify and measure the role of genes in determining behavior here....

Twin studies have one major advantage. Given that monozygotic twins share the same genes and the same prenatal environment then if they are well designed and carefully conducted they can estimate how likely a physical characteristic or behavioural trait is inherited. However, it is difficult to find monozygotic twins that do not share the same childhood environment. This makes it difficult to control for the effects of that shared physical and social environment on the behaviour the psychologist is interested in. This is why psychologists are really interested in Monozygotic twins that have been separated in early childhood and reared apart. If both twins behave in the same or similar ways even though they were raised in very different environments then this can be interpreted as evidence that the behaviour is inherited and it does have a genetic basis.

The Krays were monozygotic twins and they were both aggressive and violent. Watch the film and decide which is the most important: the fact that they are monozygotic twins and share the same genes and prenatal environment or the physical and social environment that they were raised in?

Explain their aggression using the biological approach: they have inherited their aggression and it has a genetic basis. Back up your argument with evidence from twin studies research.

How would social learning theory explain the aggression of the Krays? Use this to evaluate a genetic explanation for their behaviour. Back up your argument with evidence from research. You could always conclude that it might be both genes and environment, that there is no real debate: it's both nature and nurture. Finally you could have a look at this...epigenetics.