Ch 6 = Genetics and Personality

Ch 6 = Genetics and Personality

1. Introduction to Behavioral Genetics 2. Heritability of 3. on Personality


Jim twins– Identical

– Jim Springer & Jim Lewis!

– Both = 180 pounds, 6 feet tall

• First wives = Linda!• Second wives = Betty!


Jim twins

• Salem cigarettes• Miller Lite

– Other

– How much do our genes contribute to• Personality?• Attitudes, preferences?


Benefits– 1. – 2. – 3.

Issues– 1. ? “ my genes, not me”

(psychopathy)– 2. “designer babies”, weeding out

“unfit”


Human genome

Sequencing the entire genome– First draft =– (what does this mean?)


Human genome– Most genes are identical

– Yet, • Brown/blue eyes• Unique genes must play a role


– Danny DeVito ~ 5 feet– Shaquille O’Neal ~ 7 feet

What causes such dramatic diffs?

In fact


Heritability

– Of a• Height• Aggressiveness• Neuroticism

– Due to


Size

Conventionally

– E.g., 1 - .5 = .5, suggesting .5 variance due to envt


Misconceptions 1.

– Height is 90% heritable =– Michael’s height is 90% heritable =

2. – Height in middle ages vs. today


Heritabilities matter more for some stuff

– Mate characteristic preferences =


Behavior genetic methods– 1. Selective breeding– 2. Family studies– 3. Twin studies– 4. Adoption studies


Selective breeding

• Pit bulls - aggression• Labradors - sociability• Chesapeake Bay retriever - to fetch

– Selective breeding• Other methods for humans…


Family studies– Trait should be more similar

• For more similar family members

• Parents =

• Each parent with a child =

• Siblings =

• Grandparents =

– Potential problem


Twin studies– Identical (100%) more similar than fraternal (50%)?

• But zygote divides into 2 individuals• Must be same sex

• 2 separate sperm/egg combinations• Gestated at same time


Heritability– =– Height

• r

• r

– Plugging in values• Heritability =

• Height 90% heritable

• Rest of 10% given to envt


Adoption method– Adoptive parents

• If envt has effect, children should be similar to adoptive parents

– Genetic parents

• If genes have effect, children should be similar to biological parents


Heritability findings: Personality traits

– 50% of E, N predicted by genes– Typical finding

• Mz = • Dz = • Heritability =


Heritability findings: Temperament-like variables– 1.

• Spinath et al. (2002)• Found heritability of movement

– 2. Other temperament• Emotionality, sociability, persistence


Heritability of personality, summary– 1.

• Those that seem• Those that seem

– 3. Genes major contributor• To stability/lack of change for personality


Sexual orientation

– Is sexual orientation heritable?• Conventional wisdom = yes• Early Bailey studies

– But these studies were criticized

– Small n

– Unrepresentative samples


Sexual orientation– Bailey et al (2000)

– 92% exclusively heterosexual

• Significant, but much smaller than previously thought


• If mz twin smokes, 16x more likely to smoke oneself

• But heritabilities a bit inconsistent, .3-.5

• More heritable• .5-.6


Marriage

– Whether one marries or stays single

– Marital satisfaction


Martin et al (1986): heritable contribution to– Attitudes toward Sabbath observance– Divine law

– Interest in becoming religious figure (e.g., priest)


Plomin et al (1990)

– 20% due to shared envt (e.g., presence of TV, TV-watching parents)

Lykken & Tellegen (1996)

Predicting happiness– Education – SES – Income – Marital status – Demographics


– DZ twins– Rate happiness– Age 20 & age 30

– Twin 1 20 & twin 1 30, r = .6

– Twin 1 20 & twin 2 30, r = .48

– = .48/.60 = .80


Conclusions– 1. “The reported WB of one’s identical

twin…is a far better predictor than one’s own life circumstances”

– 2. “trying to be happier is like trying to be taller…counterproductive”

– 3. “individual differences in human happiness…are primarily a matter of (genetic) chance”


• Eros = love at first sight• Ludus = don’t get to serious, just fun• Storge = value reliability in partners• Pragma = pragmatic, mate with similar other• Mania = love-sick (e.g., insomnia when in love)• Agape = selfless; enjoy giving


– But…

• 1. Error: no test is error-free• 2. Shared envt• 3. Unshared envt


– Same parents– Same toys– Same schools, neighborhoods

– E.g., different treatment from parents– E.g., diff friends at school– E.g., one at paint chips


Shared vs. unshared: which matters more?– Shared

– Unshared


Shared envt = nothing?

• Religious beliefs• Political orientation• Health behaviors (like diet, exercise)

Behavioral Genetics

Parenting - not very relevant?

• Which sperm/egg combo was given• Sorry, wrong sperm!

Behavioral Genetics

What about adopting children?

• No genes• Shared doesn’t matter much

– What is the point of adoption then?


Challenge to environmentalism– Must recreate itself

– “why are children in same family so diff from each other?”

Ch 6 = Genetics and Personality

Documents

Transcript of Ch 6 = Genetics and Personality