chapter 6 genetics and personality click to edit master subtitle style 1© 2015 m. guthrie yarwood

© 2015 M. Guthrie Yarwood 1

Chapter 6Genetics and Personality

Click to edit Master subtitle style


Part Two. Biological Domain!!

• Chapter 6: Do our genes influence our personality traits?

• Chapter 7: Do our physiological systems (e.g., brain structures) influence our personality traits?

• Chapter 8: How are personality traits adaptive (Evolutionary Theory)?


Outline

• What is heritability?

• Types of Designs

• Problems with heritability studies

• Gene-Environment Interactions

• Current Research on heritability of personality

Heritability and Environment

• Heritability– degree to which genetic differences among

individuals cause differences in an observed property

• Environment– degree to which environmental differences

cause differences in observed property


Misconceptions About Heritability

• Heritability CANNOT be applied to single individual

• Heritability is NOT constant or unchangeable

• Heritability is NOT a precise statistic


Twin Studies


Monozygotic Twins

(MZ) Similarity

in Personalit

y

Dizygotic Twins (DZ) Similarity

in Personalit

y


Measuring Heritability

• Heritability – h = 2 (rMZ – rDZ)

• Shared/Common Environmental Effects – c = rMZ – h

• Nonshared/Unique Environmental Effects – e = 1 – rMZ

• To Check Answers: h + c + e = 1


In-Class Exercise

• A researcher is interested in determining the contribution of genes and environment to Agreeableness (A). She obtains 500 pairs of identical twins and 500 pairs of fraternal twins. The twins complete self-report measures of the HEXACO scale. She determines that the personality similarity correlation between the identical twins is .98. The personality similarity correlation between the fraternal twins is .63.

Adoption Studies

• Agreeableness – Genetics or Environment?

• We find a positive correlation between adopted children and their adopted parents

• We find a positive correlation between adopted children and their biological parents



Problems with the designs?

• Child of Our Time Video Start at 2:30

• Family Study

• Twin Study

• Adoption Study

https://www.youtube.com/watch?v=ZPARahJglnA&list=PLipH-NoQVkDLYQ8PS5c9HhXhyUl9ngvFK&index=3



• Assimilation and Contrast Effects

• Equal Environments Assumption

• Assortative Mating

• Selective Placement


Selective Placement

• Adopted parents (vs. biological parents):– Lower levels of: antisocial behavior, drug/alcohol

abuse– Higher levels of SES

• Adopted vs. biological parents no differences:– Levels of depression– Quality of family relations– Negative peer influences on children

• Outcome on adopted children(McGue et al., 2007)



• Assimilation and Contrast Effects

• Equal Environments Assumption

• Assortative Mating

• Selective Placement

• Sharing Early Environment

Genotype x Environment Correlations

G / E Correlations

Passive Evocative Active

Genotype x Environment Correlations

• Passive G/E Correlation– Rearing environments that biological parents provide

are influenced by parents’ own genes

Parents’ Genotype

Child’s Rearing Environment

Child’s Genotype

Genotype x Environment correlations

• Evocative G/E Correlation– Our heritable attributes affect others’ behavior

toward us and thus influence the social environment

Child’s Genotype

Behavior of others toward

child

Environ. Influence on

child’s development

Genotype x Environment correlations

• Active G/E Correlation– Genotypes influence the types of environments that

we prefer and seek out

Child’s Genotype

Preference and selection of

environment

Environ. Influence on

child’s development

Identify the Correlation!

• Passive G/E Correlation

• Evocative G/E Correlation

• Active G/E Correlation

• Video (start at 5 minutes)• Video Part II

19

https://www.youtube.com/watch?v=wzS_k2_fdpk

https://www.youtube.com/watch?v=JjpCDvSQTWM

Influence of G/E correlation as a function of age


SO, WHAT DOES DETERMINE OUR PERSONALITY?


Typical correlations of personality trait levels between relatives of various kinds

Type of relative CorrelationIdentical twins raised together .45

Identical twins raised apart .45Fraternal twins raised together .20

Nontwin biological siblings raised together .20Parent and biological child (together) .10 - .15

Parent and biological child (apart) .10 - .15Adoptive siblings .00 - .05

Adoptive parent and child .00 - .05

Note. Averages across different traits and different samples of persons. Table adapted from Ashton (2013)


Big Five: Genetics or Environment?

rMZ rDZ h2 c2 e2

Self-report .54 .27 .54 0 .46

Observer-report .45 .20 .50 -.05 .55

Average of Self and Observer Reports .65

(GOSAT; Borkenau et al., 2001)

© 2015 M. Guthrie Yarwood 24(Loehlin, 1997)

Unique Environment Effects

• 800 MZ and DZ Twin-Pairs

• Self-report measures:– Personality Traits– Differences in parental treatment– Differences in peer groups


Twins age 14 delinquent behavior

Twins age 17 deviant friends

Twins age 14 deviant friends

Twins age 17 delinquent behavior

(Burt et al., 2009)

Unique Environment Effects


Family Study: Neuroticism

• 34, 580 sibship pairs, 30-50 years old, southwest England

• Phenotypic Measure: Neuroticism (EPQ)

• Genotypic Measure: DNA extraction with mouthswab

• Findings: chromosomes 1, 4, 7, 12, and 13 influence Neuroticism

(Fullerton et al., 2003)

What are some unique environmental effects?

Birth Order Activity

• What is your birth order?– First, middle, last, only child

• Compare your birth order personality to your siblings (or cousin).– Similarities in Big Five? Differences in Big Five?

• How does your birth order explain these personality differences?

With an X, indicate the sibling who scores the highest on the following 5 personality traits.

Birth Order Name Openness to experience Conscientious Extraversion Agreeableness Neuroticism

First-born Michelle I I I I I

Second-born Michael I I I I I

Third-born Steven I I I I I I

Fourth-born Julie I I I I I

Birth Order Activity


Why did the first child score the highest on the traits you selected?

• Mom on Michelle’s C : The first born is the only child alone with the parents and imitates her parents behavior including being a mother. Michelle mothered her 3 siblings and became very responsible at a young age.

• Steven on Michelle’s C: I do not know why, but michelle has always been organized and loves control. I do not think it has anything to do with birth order.

• Julie on Michelle’s C and N: The oldest child feels like the third parent of all the children and must be in control, therefore has a tendency to be orderly and disciplined. The oldest child may be hostile after many years of taking care of the younger siblings which as also lead towards irritability.


Why did the last-born child score the highest on the traits you selected?

• Mom on Julie’s Neuroticism and Extraversion: She scored second highest on Conscientious. She imitated not only her parents but her sister as well. Julie is extraverted and has test anxiety for every test.

• Steven on Julie’s Neuroticism: Because she is always high strung about Dave and Work. I do not think it has anything to do with birth order.

• Julie on her Agreeableness: The last child was also striving to please the other siblings, leading to generosity and trust among them.


Why did the middle-born children score the highest on the traits you selected?

• Steven: I believe it has to do with experience and environment over time. If all of us simply went to different universities, that alone would drastically change everything about our lives, and personality. For instance if Mike went to the marines out of high school, he could have ended up the most orderly and disciplined out of the four. If I did not go to West Virginia who knows what would I have become.

• Julie on her Agreeableness: Michael may have been more extroverted in order to gain attention from the competing sibling and parents. Steven may have a larger imagination in order to be entertained throughout his life as there was always an older and younger sibling getting attention from parents and other siblings.


Nomination Procedure

• Select the sibling who scores highest in the trait.

• Problems with this method?

• First, Adler• Then, Sulloway

– Competition for parental investment causes sibling rivalry

– Birth order provides a strategy for children to compete for parental love and favor

• Unique environmental effect

Siblings: Birth Order and Personality

• Firstborns – Arrive first and secure position by identifying with parents’ personality– More C (responsible, achieving)- seek parents’ favor by acting as a

surrogate parent– More Extraversion b/c defend their status quo with dominance,

assertiveness– More Neurotic – anxious about maintaining their status

• Laterborns – find older, dominant sibling is favored by parents, so look for other ways to improve standing– Laterborns high in OE b/c more accepting of revolutionary ideas– High in A b/c adopt traits opposite of firstborn – sociable,

empathetic, altruistic

Siblings: Birth Order and Personality (Sulloway)

• Middle Children – lack advantages of being first or last– Parent will invest in firstborns (closest to reproductive age) and lastborns (most

vulnerable to disease)– More independent of family, more peer-oriented

• Only Children – no sibling rivalry– High C b/c conform to parental authority– Not More Neurotic or Less Extraverted than other children

Siblings: Birth Order and Personality (Sulloway)

• Nomination Procedure (Paulhus et al., 1999)

– First-born: highest in C; Later-born: highest in A

• 9 adopted sibship pairs (Beer & Horn, 2000)

– All biologically first born, but raised in different rearing orders– Compared first-reared to later-reared

• Firstborns more Conscientious (Beer & Horn, 2000; Healey & Ellis, 2006)

• Laterborns more OE (Healey & Ellis, 2006)

• But other research….Firstborns more OE (Michalski & Shackelford, 2001)

• Any relationship b/w birth order and personality is weak

Siblings: Birth Order: Was Sulloway Correct?


Summary

• Family, twin, and adoption studies help us to tweeze apart genetic and environmental influences– But, problems still exist for these studies

• The contribution of genes to personality ranges from 40 to 50%

• Unique, not shared, environmental effects

• Genes determines our personality stability, but unique environmental effects determine personality change.

chapter 6 genetics and personality click to edit master subtitle style 1© 2015 m. guthrie yarwood

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