Twins Flashcards
Why are individual differences so important?
They have a great influence on behaviour, so when combined with broad generalisations - we get a much deeper understanding of behaviour.
On which two characteristics is there the most emphasis?
Personality and Intelligence
Before introducing twin studies
Talk about how researchers look at the impact nature (genes), nurture (environment) - their individual impacts, and how they can they can be DEPENDANT on each other = genotype-environment interaction (concept) - BEHAVIOURAL GENETICS.
Twins do what to nature and nurture?
Distangle
What is heritability?
It is an estimate of how much genetics contributes to a trait (e.g personality or intelligence)
The estimate is a PROPORTION OF VARIANCE IN A TRAIT - in a given population, that be can be accounted for by genetic differences amongst individuals.
Identical twins are known as, non-identical twins are known as
Monozygotic, Dizygotic
What does the twin study measure?
It measures how often a CHARACTERISTIC co-occurs in identical twins as compared to non-identical twins.
What is the difference between identical and non-identical twins and where does it stem from?
Fertilised egg
Identical genes, 50% like regular siblings.
What are the two main critiques of the twin method?
Equal Environments Assumption (this condition has to hold, for resultant interpretations to be considered true).
Gene environment interaction
If EEA isn’t true, what does it potentially show, which case study backs this up?
In studies that potentially assume genetic basis, there may be environmental factors in play.
I.e those twin correlations
Treatment effects
Evans, 2000
What’s the assumption that is mentioned in defence of EEA?
They are balanced based on demographic correlates - socio-economic, that CHARACTERISTIC specific causal environmental variables have been acknowledged.
It’s not a perfect practice.
The given differences per characteristic in terms of the set of causal variables also makes this difficult to test, researchers don’t have a strong understanding of these.
Gene-environment interaction - what is it, and what exactly do researchers believe
Ongoing studies have led researchers to believe that rather then genes and environment have separate impacts, it could be actually be due to their interaction and co-dependancy that results in influencing a characteristic, where GENETIC PREDISPOSITIONS are activated by ENVIRONMENTAL STRESSORS.
Such studies suggest that there are very independent gene factors that underly complex characteristics.
Which case studies demonstrate the gene-environment interaction on individual difference variation with regards to personality?
Loehlin, 1998 - in which he tested McRae & Costa’s assumption that genetic factors accounted for some of the variation in individual differences, in which Loehlin found that 42 to 49% was due to specific events unique to the individual and to gene-environment interactions.
Haworth 2009 - which showed how the heritability of cognitive ability increased with age, from 41% at 9 years old, to 66% by young adulthood (aged 17), which was though to be related to gene-environment correlations in which as the child grows, it selects, creates, modifies experiences based on genetic propensities.
Overall - what do researchers believe?
They believe that limitations and assumptions exist, but that they don’t negate the USEFULNESS of TWIN STUDIES.
What studies suggests that the environment bias isn’t sufficient enough to INVALIDATE the CENTRAL CONCLUSION of twin studies?
Plot in & Daniels, 1987
They argued that these should be viewed as mechanisms whose relevance CAN be tested, using modified study designs that go BEYOND the classic twin study.
