Twin Studies Quiz

In the biological approach, twin studies are used to investigate the ________ ________ of behaviour.

If a twin study finds that a behaviour does have a genetic basis, then this means...

• a) The environment contributes to phenotype

• b) Phenotype contributes to genotype

• c) Genotype contributes to phenotype

• d) Phenotype contributes to the environment

The assumption underlying twin studies is that a set of MZ and DZ twins will have a ​ (a)   level of genetic similarity (100% similar for ​ (b)   twins and 50% for ​ (c)   twins) but will have a ​ (d)   level of environmental similarity (i.e., a set of MZ twins will grow up in just as ​ (e)   an environment to each other as would a pair of DZ twins (e.g., each pair will grow up in the same house, with the same parents, and the same cultural experiences).

• different
• similar
• MZ
• DZ

A criticism of the biological approach concerns a problem with its use of twin studies. The assumption underlying twin studies is that a set of MZ and DZ twins will differ in their level of genetic similarity (100% similar for MZ and 50% for DZ) but will have similar environments i.e., a set of MZ twins will grow up in just as similar an environment to each other as would a pair of DZ twins (e.g., each pair will grow up in the same house, with the same parents, and the same cultural experiences). However, this assumption may be wrong. Critics of the biological approach have argued that genetic similarity of MZ twins may actually lead them to experience a more similar environment. For example, as MZ twins look identical... [explain why this will lead them to experience a more similar environment than a pair of DZ twins]

Answer explanation

Critics have argued that because MZ twins look identical, people in their environment will tend to treat them more alike than they would treat non-identical dizygotic twins. Consequently, it may be difficult to say whether similarities in the behaviour of MZ twins is due to their similar genetic profile or their similar upbringing.  This means that it may not be possible to use twin studies to conduct research into the relative importance of heredity and the environment/nature-nurture debate.

Twin studies are like an experiment. Match the variables.

• Environmental similarity between twins

• Dependent variable

• Concordance rates

• Independent variable

• Genetic similarity between twins

• Extraneous variable

If the assumption that MZ and DZ twins have a similar level of environmental similarity to each other is wrong, this would introduce a ​ (a)   variable into twin studies, as not only would MZ twins have a more similar genotype, they would also have a more similar shared environment (i.e., there would now be two systematic differences between the conditions). Consequently, it would be impossible to know whether higher concordance rates for MZ twins were the result of genes, the environment or both genes and the environment. This would fatally undermine the ​ (b)   validity of twin studies.

• internal
• confounding
• extraneous
• indepndent
• dependent
• external
• ecological
• population

If the assumption that MZ and DZ twins have a similar level of environmental similarity to each other is wrong, this would introduce a confounding variable into twin studies, as not only would MZ twins have a more similar genotype, they would also have a more similar shared environment. Consequently, it would be impossible to know whether higher concordance rates for MZ twins were the result of genes, the environment or both genes and the environment. This would fatally undermine the internal validity of twin studies as a means of investigating the ________ ________ of behaviour.

Write a point for this paragarph that would be relevant for the following exam question

Discuss the nature-nurture debate. [16 marks]

Remember to use the wording of the question in your point

There are rare cases where DZ twins do look identical. However, these “pseudo MZ twins” (meaning they look like MZ twins but aren’t actually MZ) do not tend to have higher concordance rates than typical DZ twins.

• a) This suggests twin studies not have internal validity

• b) This suggests twin studies have internal validity