Genetics of personality and intelligence Flashcards
What did Watson believed formed personality?
- “Give me a dozen healthy infants, well-formed, and my own specified world to bring them up in and I’ll guarantee to take anyone at random and train him to become any type of specialist I might select…” – (Watson 1924/1931, p. 104)
- The environment matter for generating outcomes
- “I am going beyond my facts and I admit it, but so have the advocates of the contrary and they have been doing it for many thousands of years”
What did Pinker believed formed personality?
- “Of course genes can’t pull the levers of our behavior directly. But they affect the wiring and workings of the brain, and the brain is the seat of our drives, temperaments and patterns of thought. Each of us is dealt a unique hand of tastes and aptitudes, like curiosity, ambition, empathy, a thirst for novelty or for security, a comfort level with the social or the mechanical or the abstract.” – (Steven Pinker)
- Genes build up our personality, model of personality
How do you test if personality is formed by the environment or genes?
twin and family study designs
What is a Classical twin design?
- Uses identical (or monozygotic) and nonidentical (or dizygotic) twin pairs.
How do identical twins form?
-Identical twins – single egg fertilised by single sperm then splits into two (share all their genes)
How do non-identical twins form?
-Fraternal twins – separate eggs fertilised by separate sperm (share only about half their genes)
If only genes matter then what would it show?
- Identical twins will show the same personality traits
- Non-identical twins will only show about half the same personality traits
If only environment mattered what would it show?
-Both twin types would show the exact same personality if they are brought up by the same parents
If unique-environments are all important what would it show?
-Regardless of twin type there will be no correlation
What did Bouchard (2004) find looking at heritability and shared environment in personality?
- Review paper
- How large genetic differences are in a given sample
- If heritability is 1 mean that the extraversion causes are caused by genetic differences
- Shared environment does not have an effect
- Intelligence: heritability correlation increases with age, but decreases after 75 years old
- Shared environment: age 5 correlation is .54, but decreases to .26 by 10 and after then there is no correlation
What did Plomin and Deary (2015) find about heritability and age?
-Heritability increases from childhood to young adulthood
How and when is the environment important?
- Shared-environment effects may be more important in impoverished environments – Most twin studies use WEIRD samples
- Some evidence for shared-environment effects in childhood
- Effects seem to be transient though; genetic influences become important as one gets to select ones own niches
- Peer influences may be more critical
What is the Violation of the Equal Environment Assumption?
-In a nutshell: If MZs are treated in a special way (compared to the DZs), their greater phenotypic similarities may in fact not be because of greater genetic similarities after all!
What are the predictions if two twins are adopted into different families?
- Scenario: MZs reared in different families from early childhood meet again in adulthood…
- If family experiences shape personality: MZ twins will not be similar
- If genes shape personality: MZ twins will be highly similar
- If a combination of the two: MZs reared apart will be similar, but less so than MZs reared together
What is MISTRA?
- Minnesota Twins Reared-Apart (MISTRA) study
- Tom Bouchard (left); Matt McGue
