twin and adoption studies Flashcards
what do these studies allow us to look at?
the influence of genes on behaviour by looking at the effects of nature and nurture
what is nature?
this is related to the biological causes of behaviour (genes inherited from parents, etc)
what is nurture?
this refers to the environmental causes of behaviour (importance of upbringing, etc)
what does these studies generally investigate the role of?
twin studies - nature (genes)
adoption studies - nurture (role of environment)
both are naturalistic as the IV is always naturally occurring
what are the two types of twins?
monozygotic - identical twins
dizygotic - non identical twins
concordance rates
this is the likelihood that you will show the same characteristics (if one twin shows a behaviour, the other will too). it is usually expressed as a percentage, the higher it is the greater the shared behaviours. in twin studies, concordance rates of MZ and DZ twins are compared
MZ twins
they are conceived within the same pregnancy, with only one egg and one sperm that splits apart to form two embryos. they share 100% of their DNA. if the concordance rate for MZ twins is higher than for DZ twins, it suggests that the behaviour is more due to genes
DZ twins
they are also conceived during the same pregnancy, however they are the product of two different sperm and eggs. they share 50% of their DNA. if the concordance rate is higher for DZ twins than MZ twins it would suggest that the behaviour is more due to environment
what do twin studies control for?
social environment, hypothesising that the environment is similar for the twins as they are generally raised in the same social environment so the impact of it is considered to be equal and consistent. however, MZ twins are often treated more similarly than DZ twins, which may also cause them to have higher concordance rate due to having more shared experiences
describe twin studies
they are used to look at nature and nurture and how they affect behaviour, they usually use twins that were separated at birth and then reunited in adulthood to do this, e.g. the Jim twins. statistics are measured using concordance rates with percentages from 0-100%. if the concordance rate is higher for MZ twins than DZ twins it would suggest that behaviour is more due to genetics as MZ twins share 100% of their genes whereas DZ twins are 50%.
Johannes Lange (1929)
he studies 30 twin pairs - 17 were DZ and 13 were MZ. at least one twin of each pair was known to have committed a crime, lange found that 10/13 MZ twin pairs were known criminals whereas this was only the case in 2/17 DZ twin pairs. this suggests that behaviour is more affected by genes than environment
twin studies evaluation
- a weakness is that there is low validity due to the possibility of confounding variables. just because twins share the same home life, they may have different friends and interests and these differences may become more pronounced as the twins grow older. therefore, there is decreased accuracy as, although twins share the same genotype, they don’t share the same phenotype
- there is high clinical application as twin studies can tell us whether behaviours are heritable, this is important for treating disorders like schizophrenia as it tells us which treatment is best to be used - bio treatments or whether o be careful of triggers as due to nurture. therefore, if at risk children are identified early they can be helped as soon as possible
what are adoption studies?
studies where adopted children are compared with their biological parent and an adoptive relative (adoptive parent or sibling). if they have similarities with their biological family then behaviour is more due to nature and if they’re with their adoptive relatives its mostly due to nurture
what is a heritability rate?
the extent to which a trait is inherited through genes. a figure of 0%would mean that genes don’t contribute to individual differences and 100% would mean that ends are the sole reason for individual differences
crowe (1972)
compared a group of children with their biological mother who either had a criminal record (experimental group) or had no previous convictions (control group). it was found that, if their biological mother had a criminal record, 50% of the children also had one by the time they were 18. in the control group this was only 5%
evaluation of adoption studies
- a strength is that their is high validity as adoption studies allow for genes and environment to be separated, it is controlled for as relatives are raised in different environments. therefore, there is increased accuracy as it removed the ‘environment issue.’
- a weakness is that her is low generalisability as adoptive children may not be fully representative of all children, this is because they may have experiences trauma. therefore, their behaviour may not be the same as non-adoptive children which makes results of studies are to generalise.
