Twin and Adoption Studies Flashcards
what are twin and adoption studies used for ?
to investigate the effects of nature and nurture on behaviour
what does nature refer to ?
refers to the biological causes for behaviour
what is meant by ‘biological cause’ in nature ?
means the influence of genes that have been inherited from biological parents
what does nurture refer to ?
the environmental causes of behaviour
what is meant by ‘environmental cause’ in nurture ?
means the importance of upbringing, regardless of who the parents are
what do twin studies investigate ?
the role of nature (genes)
what do adoption studies investigate ?
the role of nurture (upbringing)
what type of experiments are twin and adoption studies always and why ?
natural experiments because the independent variable being investigated (whether you are biologically related to your family or what type if twin you are) is a naturally occurring variable
what do adoption studies look at ?
the impact of nurture on children who are raised by parents who are not their biological parents
how are adoption studies made more valid ?
if the researchers have information about the child’s biological parent
what does it mean if a child grows up with traits that resemble the adoptive parent more than the biological parent ?
this is stronger evidence that that these traits are due to nurture
what are adoption studies usually measured with ?
usually measured using a correlational technique - the researchers are looking for a correlation between the behaviour of the children and their parents
what is the interpretation to a correlation with adopted parent being higher than correlation with biological parent ?
behaviour is partly due to nurture (upbringing)
what is the interpretation with adopted parent is lower than correlation with biological parent ?
behaviour is partly due to nature (genes)
what are monozygotic twins ?
twins conceived from a single egg which later split - these twins share the same genes, this means they MUST be the same sex
what are dizygotic twins ?
twins conceived when two or more eggs were fertilised at the same time - these twins share the same amount of genes as any other brother or sister (up to 50%)
what is meant by identifying zygocity ?
deciding whether the twins are monozygotic or dizygotic
what does it mean if MZ and DZ twins behave in the same way ?
nature has little to do with the behaviour
what does it mean if MZ and DZ twins behave differently ?
suggests nature is at work - because the shared environment is nit producing the same behaviour so genetic differences could explain this
what are twin studies measured with (statistic) ?
concordance rate
what does concordance mean ?
“agreement” - if one twin shows a behaviour and the other twin does too, this is concordance
what does 100% concordance mean ?
all the twins shared the behaviour in common (0% means none of them did)
how is concordance rate used in twin studies ?
the concordance rate of the MZ twins is compared to that of the DZ twins
what does it mean if MZ concordance is significantly higher than DZ concordance ?
behaviour partly due to nature
what does it mean if MZ concordance is similar to DZ concordance ?
behaviour entirely due to nurture
what does it mean if MZ concordance is 100%
behaviour entirely due to nature
what does it mean if MZ concordance is significantly less than 100% ?
behaviour partly due to nurture
what are two similarities of twin and adoption studies ?
1) adoption and twin studies are both natural experiments
2) both these methods focus on comparing people who share genetic material with people who share less genetic material while environment factors remain constant
why are twin and adoption studies natural experiments ?
they study the influence of genetics and environment on behaviour - but they do this by observing naturally-occurring variables rather than manipulating IVs in a lab - this means they avoid a lot of ethical problems with manipulation humans in lab settings
what are three differences between twin and adoption studies ?
1) twin studies are much better at studying the effects of nature (genes)
2) adoption studies are much better at studying the effects of nurture (upbringing)
3) adoption studies don’t face the problem of assigning zygocity to twins, which can be unreliable
why are twin studies better at studying the effects of nature ?
because MZ twins share 100% of their genes, whereas adopted children do not share 100% if their genes with either their biological parents - concordance rates between MZ twins tells us more than it does between children and their biological parents
why are adoption studies better at studying the effects of nurture ?
we cannot be sure how little twins share the same environmental influences (Phenotype) - but we can be sure that adoptive parent provide almost all the upbringing of the adoptive children and that the biological parents contribute little to nothing
what problem do twin studies avoid that adoption studies have ?
they don’t have the problem of tracking down biological parents and persuading them to take part in the study - because of migration and ease of trace in the 21st century, this problem may be greater than it used to be
what is a strength of twin studies ?
- they are a valid way of investigating the nature v nurture debate
- MZ twins naturally share a genotype with their twin so the researchers are not manipulating this variable and so the risk of researcher bias is reduced
- this also avoids ethical problems
what is a weakness of twin studies ?
- difficult to generalise because they are rare
- twins may have unusual lives that make them different to other children (e.g. they attract attention and often get treated the same way)
- this may lead them to behave in a more similar way than normal siblings
- this means that they might not be very representative pf other children and so they are less useful
how might the results from twin studies be invalid ?
- it is hard to identify MZ twins without DNA tests
- DZ twins can look similar and have the same blood group and similar fingerprints (commonly used tests)
- if studies misidentify the zygocity of the twins then the studies become invalid and will lack credibility
