ch 6 = genetics and personality
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Ch 6 = Genetics and Personality
1. Introduction to Behavioral Genetics 2. Heritability of 3. on Personality
Ch 6 = Genetics and Personality
Jim twins– Identical
– Jim Springer & Jim Lewis!
– Both = 180 pounds, 6 feet tall
• First wives = Linda!• Second wives = Betty!
Ch 6 = Genetics and Personality
Jim twins
• Salem cigarettes• Miller Lite
– Other
– How much do our genes contribute to• Personality?• Attitudes, preferences?
Ch 6 = Genetics and Personality
Benefits– 1. – 2. – 3.
Issues– 1. ? “ my genes, not me”
(psychopathy)– 2. “designer babies”, weeding out
“unfit”
Ch 6 = Genetics and Personality
Human genome
Sequencing the entire genome– First draft =– (what does this mean?)
Ch 6 = Genetics and Personality
Human genome– Most genes are identical
– Yet, • Brown/blue eyes• Unique genes must play a role
Ch 6 = Genetics and Personality
– Danny DeVito ~ 5 feet– Shaquille O’Neal ~ 7 feet
What causes such dramatic diffs?
In fact
Ch 6 = Genetics and Personality
Size
Conventionally
– E.g., 1 - .5 = .5, suggesting .5 variance due to envt
Ch 6 = Genetics and Personality
Misconceptions 1.
– Height is 90% heritable =– Michael’s height is 90% heritable =
2. – Height in middle ages vs. today
Ch 6 = Genetics and Personality
Heritabilities matter more for some stuff
– Mate characteristic preferences =
Ch 6 = Genetics and Personality
Behavior genetic methods– 1. Selective breeding– 2. Family studies– 3. Twin studies– 4. Adoption studies
Ch 6 = Genetics and Personality
Selective breeding
• Pit bulls - aggression• Labradors - sociability• Chesapeake Bay retriever - to fetch
– Selective breeding• Other methods for humans…
Ch 6 = Genetics and Personality
Family studies– Trait should be more similar
• For more similar family members
• Parents =
• Each parent with a child =
• Siblings =
• Grandparents =
– Potential problem
Ch 6 = Genetics and Personality
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
Ch 6 = Genetics and Personality
Heritability– =– Height
• r
• r
– Plugging in values• Heritability =
• Height 90% heritable
• Rest of 10% given to envt
Ch 6 = Genetics and Personality
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
Ch 6 = Genetics and Personality
Heritability findings: Personality traits
– 50% of E, N predicted by genes– Typical finding
• Mz = • Dz = • Heritability =
Ch 6 = Genetics and Personality
Heritability findings: Temperament-like variables– 1.
• Spinath et al. (2002)• Found heritability of movement
– 2. Other temperament• Emotionality, sociability, persistence
Ch 6 = Genetics and Personality
Heritability of personality, summary– 1.
• Those that seem• Those that seem
– 3. Genes major contributor• To stability/lack of change for personality
Ch 6 = Genetics and Personality
Sexual orientation
– Is sexual orientation heritable?• Conventional wisdom = yes• Early Bailey studies
– But these studies were criticized
– Small n
– Unrepresentative samples
Ch 6 = Genetics and Personality
Sexual orientation– Bailey et al (2000)
– 92% exclusively heterosexual
• Significant, but much smaller than previously thought
Ch 6 = Genetics and Personality
• If mz twin smokes, 16x more likely to smoke oneself
• But heritabilities a bit inconsistent, .3-.5
• More heritable• .5-.6
Ch 6 = Genetics and Personality
Marriage
– Whether one marries or stays single
– Marital satisfaction
Ch 6 = Genetics and Personality
Martin et al (1986): heritable contribution to– Attitudes toward Sabbath observance– Divine law
– Interest in becoming religious figure (e.g., priest)
Ch 6 = Genetics and Personality
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
Lykken & Tellegen (1996)
– 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
Lykken & Tellegen (1996)
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”
Ch 6 = Genetics and Personality
• 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
Ch 6 = Genetics and Personality
– But…
• 1. Error: no test is error-free• 2. Shared envt• 3. Unshared envt
Ch 6 = Genetics and Personality
– 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
Ch 6 = Genetics and Personality
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?
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