Ch 6 Genetics and Personality

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Ch 6 Genetics and Personality

• 1. Introduction to Behavioral Genetic Studies (Ch
  6)
• 2. Heritability of Personality, Sexuality, etc.
• 3. Environmental Effects
• 4. Happiness Genetic?

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Ch 6 Genetics and Personality
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Ch 6 Genetics and Personality

• Jim twins
• Names
• Jim Springer Jim Lewis
• Met for first time at age 39
• Both 180 pounds, 6 feet tall
• Both married twice
• First wives Linda
• Second wives Betty

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Ch 6 Genetics and Personality

• Jim twins
• Tastes
• Other similarities
• Same headaches
• Same habit of biting fingernails
• How much do our genes contribute to
• Personality?
• Attitudes, preferences?

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Ch 6 Genetics and Personality

• Human genome
• 30,000-40,000 genes
• Sequencing the entire genome
• First draft June 26, 2000

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Ch 6 Genetics and Personality

• Human genome
• Most of our genes are identical
• This produces faces, eyes, fingers, so on
• Common things to all of us
• Some of our genes differ
• Blue eyes versus brown
• Blond hair versus black, so on
• Some of these diffs must somehow account for
• Heritable aspects of personality
• Although we dont know much about this yet, we
  know some

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Ch 6 Genetics and Personality

• Height
• What causes such dramatic diffs?
• In fact
• Both true
• However, 90 due to genetics
• 10 due to envt factors
• This is specific to US, adequate food availability

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Ch 6 Genetics and Personality

• Heritability
• Height
• Aggressiveness
• Neuroticism
• Still, such heritability coefficients
• Not absolute
• Will differ by populations under study
• Thus, heritability is population-specific

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Ch 6 Genetics and Personality

• Heritability coefficients
• Conventionally, but perhaps not warranted
• In any case
• Inverse relation between heritability envt
  contribution

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Ch 6 Genetics and Personality

• Misconceptions about heritability
• 1.
• Height is 90 heritable is OK
• Michaels height is 90 heritable doesnt make
  sense
• Heritabilities are at the population level
• 2.
• They reflect the specific population in question
• Will change in other populations, historical
  times
• E.g., height is probably more heritable in US
  than Middle Ages (more diseases malnutrition)

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Ch 6 Genetics and Personality

• Heritabilities differ
• Height
• Weight
• Preferences for marital partner
• Genes matter more for some stuff than other stuff

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Ch 6 Genetics and Personality

• 1. Selective breeding
• 2. Family studies
• 3. Twin studies
• 4. Adoption studies

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Ch 6 Genetics and Personality

• Selective breeding
• If it can be bred, there is a genetic basis to it
• Pit bulls bred for aggression (humans did this)
• Labrador bred for sociability
• Chesapeake Bay retriever
• Bred to fetch stuff
• Selective breeding works
• Thus must be a genetic basis to dog personality,
  behavior
• Cannot of course selectively breed humans
• Other methods necessary

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Ch 6 Genetics and Personality

• Family studies
• Amount of shared genes should predict
• Extent of personality similarity
• Shared genes
• Potential problem

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Ch 6 Genetics and Personality

• Twin studies
• Compare similarity of personality of
• Identical twins
• Same sperm egg
• But zygote divides into 2 individuals
• Must be same sex
• 1/3 of twins
• Fraternal twins
• 2 separate sperm/egg combinations
• Gestated at same time
• Can be same or opposite sexes
• 2/3 of twins

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Ch 6 Genetics and Personality

• Heritability
• 2 (r mz - r dz)
• Height
• r .93
• r .48
• Plugging in values
• Heritability 2(.93 - .48) .90
• Height 90 heritable
• Rest of 10 given to envt

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Ch 6 Genetics and Personality

• Adoption method
• 0 shared genes
• But shared envt
• If envt has effect, children should be similar to
  adoptive parents
• 50 shared genes
• But not shared envt
• If genes have effect, children should be similar
  to biological parents

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Ch 6 Genetics and Personality

• Heritability findings Personality traits
• Typical finding
• Mz .51
• Dz .21
• Heritability 2(.51-.21) .6

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Ch 6 Genetics and Personality

• Adoption studies
• Typically, no correlation between personality of
  adoptive parents adopted child
• Thus, parenting doesnt seem to shape E, N much
  if at all

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Ch 6 Genetics and Personality

• Heritability findings Temperament-like variables
• 1. Activity level
• 2. Other temperament variables (e.g.,
  emotionality, sociability, persistence)

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Ch 6 Genetics and Personality

• Heritability of personality, summary
• 1. Almost any trait looked at shows, on average,
  .5 heritability
• 2. True for traits that seem inborn (e.g.,
  activity level) as well as for traits that seem
  socialized (e.g., morality)
• 3. Heritability is a major contributor to
  stability of personality

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Ch 6 Genetics and Personality

• Sexual orientation
• Sexual orientation is pretty stable over time
• Especially for men
• Is sexual orientation heritable?
• Conventional wisdom yes
• Early Bailey studies yes .3-.7
• But these studies were criticized
• Small n
• Unrepresentative samples

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Ch 6 Genetics and Personality

• Sexual orientation
• Bailey et al (2000)
• Large study
• Random selection to avoid unrepresentative
  samples
• 1,000 pairs of mz 1,000 pairs of dz
• 92 exclusively heterosexual
• Homosexual women
• Less exclusive
• More plastic in sexual behavior
• Heritability

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Ch 6 Genetics and Personality

• Drinking, smoking
• Smoking is heritable
• Alcohol use is heritable
• Alcoholism

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Ch 6 Genetics and Personality

• Marriage
• Whether one marries or stays single
• Marital satisfaction
• But especially wives influence on marriage

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Ch 6 Genetics and Personality

• Martin et al (1986) heritable contribution to
• Attitudes toward Sabbath observance
• Divine law
• Church authority
• Bible as truth
• Fundamentalism
• Interest in becoming religious figure (e.g.,
  priest)

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Ch 6 Genetics and Personality

• 30 of it has genetic basis
• 20 due to shared envt (e.g., presence of TV,
  TV-watching parents)

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Ch 6 Genetics and Personality

• Waller Shaver (1994)
• Love styles
• Eros love at first sight
• Ludus dont 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

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Ch 6 Genetics and Personality

• Shared unshared envt
• Heritability envt variation 1
• Therefore, heritabilities below 1 would suggest
  envt contribution
• Envt variation
• Actually three things
• 1. Error no test is error-free this error gets
  thrown in envt variance
• 2. Shared envt
• 3. Unshared envt

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Ch 6 Genetics and Personality

• Influences that would be common (e.g., to twins
  reared together)
• Same parents
• Same toys
• Same schools, neighborhoods
• Socialization influences unique to one twin
• E.g., different treatment from parents
• E.g., diff friends at school

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Ch 6 Genetics and Personality

• Shared vs. unshared which matters more?
• Shared
• Unshared
• Study of nonshared influences is recent
• Given their obvious importance
• Future research will focus on such influences

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Ch 6 Genetics and Personality

• Shared envt worth nothing, then?
• Well, worth less than traditionally thought
• Still has influence in certain areas
• Attitudes
• Religious beliefs
• Political orientation
• Health behaviors (like diet, exercise)

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Behavioral Genetics

• More about parenting
• If being good or bad parents has little
  effect, what is the point of parenting
• Well, some influence on likelihood of juvenile
  delinquency, perhaps criminality, expectations
  about romantic love (but not personality, IQ)
• Well, parenting is insuring the survival of your
  genes
• Parents do matter
• Not in terms of what they do, how they raise
  children
• More in terms of contributing DNA

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Behavioral Genetics

• More about parenting
• What about adopting children?
• No effect (through genes or child rearing) on
  personality, IQ
• Children will have more in common with biological
  parents than you, even if they never see
  biological parents
• What is the point of adoption?
• Adoptees as entertainment devices?

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Ch 6 Genetics and Personality

• Challenge to environmentalism
• Must recreate itself to focus on unshared aspects
  of envt
• why are children in same family so diff from
  each other?

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Lykken Tellegen (1996)

• Envt effects on happiness

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Lykken Tellegen (1996)

• Education
• SES
• Income
• Marital status

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Lykken Tellegen (1996)

• Genetics
• DZ twins
• Rate happiness
• Age 20 age 30
• Stability of happiness
• Twin 1 20 twin 1 30, r .6
• Genetics of happiness
• Twin 1 20 twin 2 30, r .48
• of stable happiness due to genes
• .48/.60 .80

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Lykken Tellegen (1996)

• Conclusions
• 1. The reported WB of ones identical twinis a
  far better predictor than ones own life
  circumstances
• 2. trying to be happier is like trying to be
  tallercounterproductive
• 3. individual differences in human happinessare
  primarily a matter of (genetic) chance