METHODS of studying biological traits??? How else can you examine biological links to behaviour? Brain storm

Methods: Adoption and Twin Studies

Link to Issues and Debates: Nature-nurture ?? Where do you stand? Aggression is a biological trait.

Using twin studies One way of finding out whether a disorder has a genetic component is to see whether it runs in families. If relatives of sufferers have a higher than average risk of getting the disorder themselves, then it may be that the disorder has a genetic component. However, family members typically share similar environments. Consequently, increased risk amongst close relatives may simply indicate that that are exposed to the same set of environmental risks. An alternative approach is to do a twin study. This looks at the concordance rate (degree of similarity) of twins with respect to the disorder being considered. Concordance rates means the probability of one twin having the disorder if the other already has it expressed as a percentage

TWIN Study In a twin study, MZ (identical) and DZ (non-identical) twins are compared. Whilst MZ twins have a greater degree of genetic similarity, both types of twin pair grow up in identical environments. So if we discover that MZ twins have a higher concordance, this cannot be because their environments are more similar than those of DZ twins; it must therefore be because their genes are more similar.

Describe the findings of the graph (3 marks)

Gottesman and Shields (1966) 1) What was the aim of the study? 2) Who did they look at (who made up their sample)? 3) What types of twins did they study? 4) List two results. 5) List at least one conclusion they drew from their results. 6) What is a problem with this kind of research? 7) Why is this kind of research important? 8) How can it be applied today?

Using Gottesman and Shields (1966) Evaluate the use of twin studies in research. (8 marks) Twin studies control for the effect of genetic differences. Twin studies are useful because they can suggest that there is a link between genes and behaviour. Twin studies can be reductionist. Twin studies use correlations.

Adoption Studies One of the best methods to allow psychologists to measure whether a behaviour is the result of nature or nurture. Groups of adoptees are studies and their behaviour is correlated with their adopted families as well as their natural families. Adoptees share no genetic material with their adopted families but have a shared environment. They do share 50% of their genes with each biological parent but have not had a shared environment for the majority of their life. But if the behaviour of the adoptees is strongly correlated with the biological family and is not associated with the behaviour of the adopted family then it could be concluded that the behaviour being studies is caused by a biological component.

Cadoret and Stewart(1991) Aim, procedure and findings and conclusion This study used an adoption design to investigate the relationships among genetic background, environmental factors, and clinical outcome of attention deficit/hyperactivity and aggressivity, of 283 male adoptees. Adopted boys had an increase risk of ADHD and aggression as children if they had a biological parent who had been convicted of a crime in adulthood. The more psychiatric problems in members of the adoptive family the more likely the boy had a diagnosis of ADHD or were rated as aggressive. This suggests that….

Cadoret and Stewart(1991) Adoption Studies Evaluate the use of adoption studies in research. (8 marks) + Control for individual differences +Less reductionist -Generalisability -Correlation not causation

Exam questions Explain why studying children who have been adopted and reared apart from their biological family can help to study the nature-nurture debate (6 marks) Discuss issues involved in twin and adoption studies (12 marks) Compare twin and adoption studies (6 marks)

Stretch and challenge: In what ways do these two studies provide evidence for the nature/nurture debate?