Chapter 6 Genetics and Personality Click to edit Master subtitle style © 2015 M. Guthrie Yarwood

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

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

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

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

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

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

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. © 2015 M. Guthrie Yarwood

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

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

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

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

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

© 2015 M. Guthrie Yarwood

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 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

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

Influence of G/E correlation as a function of age

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

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) .10 - .15 Parent and biological child (apart) Adoptive siblings .00 - .05 Adoptive parent and child Note. Averages across different traits and different samples of persons. © 2015 M. Guthrie Yarwood Table adapted from Ashton (2013)

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)

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

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

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 What are some unique environmental effects? © 2015 M. Guthrie Yarwood (Fullerton et al., 2003)

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?

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

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

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

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

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

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

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

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: 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

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