1. Chapter 6 Genetics and Personality
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© 2015 M. Guthrie Yarwood

2. 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)?
© 2015 M. Guthrie Yarwood

3. Outline What is heritability? Types of Designs
Problems with heritability studies
Gene-Environment Interactions
Current Research on heritability of personality
© 2015 M. Guthrie Yarwood

4. Heritability and Environment
degree to which genetic differences among individuals cause differences in an observed property
Environment
degree to which environmental differences cause differences in observed property
© 2015 M. Guthrie Yarwood

5. Misconceptions About Heritability
Heritability CANNOT be applied to single individual
Heritability is NOT constant or unchangeable
Heritability is NOT a precise statistic
© 2015 M. Guthrie Yarwood

6. Twin Studies © 2015 M. Guthrie Yarwood
Monozygotic Twins (MZ) Similarity in Personality
Dizygotic Twins (DZ) Similarity in Personality
© 2015 M. Guthrie Yarwood

7. Measuring 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
© 2015 M. Guthrie Yarwood

8. 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 The personality similarity correlation between the fraternal twins is .63.
© 2015 M. Guthrie Yarwood

9. 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
© 2015 M. Guthrie Yarwood

10. Problems with the designs?
Child of Our Time Video Start at 2:30
Family Study
Twin Study
Adoption Study
© 2015 M. Guthrie Yarwood

11. Problems with the designs?
Assimilation and Contrast Effects
Equal Environments Assumption
Assortative Mating
Selective Placement
© 2015 M. Guthrie Yarwood

12. 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)
© 2015 M. Guthrie Yarwood

13. Problems with the designs?
Assimilation and Contrast Effects
Equal Environments Assumption
Assortative Mating
Selective Placement
Sharing Early Environment
© 2015 M. Guthrie Yarwood

14. © 2015 M. Guthrie Yarwood

15. Genotype x Environment Correlations
G / E Correlations
Passive
Evocative
Active

16. 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

17. 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

18. Genotype x Environment correlations
Child’s Genotype
Preference and selection of environment
Environ. Influence on child’s development
Active G/E Correlation
Genotypes influence the types of environments that we prefer and seek out

19. Identify the Correlation!
Passive G/E Correlation
Evocative G/E Correlation
Active G/E Correlation
Video (start at 5 minutes)
Video Part II

20. Influence of G/E correlation as a function of age

21. SO, WHAT DOES DETERMINE OUR PERSONALITY?
© 2015 M. Guthrie Yarwood

22. Typical correlations of personality trait levels between relatives of various kinds
Type of relative
Correlation
Identical twins raised together
.45
Identical twins raised apart
Fraternal twins raised together
.20
Nontwin biological siblings raised together
Parent and biological child (together)
Parent and biological child (apart)
Adoptive siblings
Adoptive parent and child
Note. Averages across different traits and
different samples of persons.
© 2015 M. Guthrie Yarwood
Table adapted from Ashton (2013)

23. Big Five: Genetics or Environment?
rMZ
rDZ h2 c2 e2
Self-report
.54
.27
.46
Observer-report
.45
.20
.50
-.05
.55
Average of Self and Observer Reports
.65
© 2015 M. Guthrie Yarwood
(GOSAT; Borkenau et al., 2001)

24. Unique Environment Effects
800 MZ and DZ Twin-Pairs
Self-report measures:
Personality Traits
Differences in parental treatment
Differences in peer groups
(Loehlin, 1997)
© 2015 M. Guthrie Yarwood

25. Unique Environment Effects
Twins age 14 delinquent behavior
Twins age 17 deviant friends
Twins age 14 deviant friends
Twins age 17 delinquent behavior
(Burt et al., 2009)
© 2015 M. Guthrie Yarwood

26. Family Study: Neuroticism
34, 580 sibship pairs, years old, southwest England
Phenotypic Measure: Neuroticism (EPQ)
Genotypic Measure: DNA extraction with mouthswab
Findings: chromosomes 1, 4, 7, 12, and 13 influence Neuroticism
What are some unique environmental effects?
© 2015 M. Guthrie Yarwood
(Fullerton et al., 2003)

27. 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?

28. Openness to experience
Birth Order Activity
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
Third-born
Steven
 I I I
Fourth-born
Julie
  I  I

29. 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.
© 2015 M. Guthrie Yarwood

30. 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.
© 2015 M. Guthrie Yarwood

31. 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.
© 2015 M. Guthrie Yarwood

32. Nomination Procedure
Select the sibling who scores highest in the trait.
Problems with this method?
© 2015 M. Guthrie Yarwood

33. Siblings: Birth Order and Personality
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

34. Siblings: Birth Order and Personality (Sulloway)
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

35. 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

36. Siblings: Birth Order: Was Sulloway Correct?
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

37. 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.
© 2015 M. Guthrie Yarwood