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Genetics of Personality & Intelligence (Twin studies (Bouchard: (Half…
Genetics of Personality & Intelligence
Causes of Personality
Watson:
"Give me a dozen healthy infants and my own specified world to bring them up in & I guarantee to take anyone and train them to be anything I want"
= A
Radical Environmentalist Claim
Pinker:
Genes and environment together
Parents
Shared-environment effects may be more important in impoverished environments
Most research used WEIRD pps
Some evidence for shared-environment effects in childhood
Genetic influences become more important as one gets to select personality
Peer
influence may be more important
E.g. in religion, politics -> change at uni
Parents effect intelligence in childhood - read to them and encourage them
Twin will be in different environments with different peers at uni
Criticisms
MZ's are treated more alike - same clothes and bedroom etc.
Therefore, twin design is biased and overstating genetic effects
Adoption Design
MZs split and raised by different families (seen during wartime)
If family purely shaped personality - twins would be completely different
Results:
Correlated with each other but not as much as twins who were raised together
Can correct some of the biases from MISTRA
MISTRA
Minnesota Twins Reared Apart
Found twins reared apart and tested similarities
MZA = MZs apart, MZT = MZs together
People who didn't grow up together were
still very similar
MZA & MZT scores were similar
Therefore, environment doesn't play a large role
Genetic Determinism
Genetic influences are mostly
probabilistic
They don't determine your outcomes - you aren't fixed to a specific number etc.
Nonetheless, if you have genes for height - you are still likely to be tall - this is the same for PDs
You can still change this though - huge growth spurts in the population over the last century (diet) = environmental
Similarly, intelligence may rise due to education and diet
Rank order may not change if its due to genetics
Twin studies
Used to know which perspective is correct
Classical design - use identical MZ and non-identical (DZ) twins
Correlate twins' personality scores -> MZs are more closely related
If
only genes
were important:
MZ would correlate at 1 (100%)
DZ would be half alike (0.5)
If
only environment
was important:
Both MZ and DZ would be at 1
Unique personalities
: MZ and DZ wouldn't correlate
E.g. if one was robbed and left them emotionally scarred
Bouchard:
Half of differences in personality seem to be due to
genetics
other half due to
unique environments
. NO shared environmental effects
Early childhood - Genes not explaining difference
Ageing - Genetic effects increase
Discovery of Genes
Gene sequence people and locate their personality from DNA
Gene studies
did not replicate
Many people were angry -> crisis
E.g. find a drug to treat depression - assume the drug will change brain behaviour
File Drawer:
Findings got left and not published
Advances
Now looking at
whole genome
- take DNA and use millions of markers to see how it relates to personality
DNA collected from schizophrenics -> 108 genome points related to schizophrenia
DeMoor:
Largest meta-analysis looking at the B-5 traits