PSYC 332 Lecture Notes - Lecture 5: Twin, Twin Study, Heritability
20 Feb 2017
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5 PSYC 332 Feb 6th 2017
Exploring genetic vs. family influences on personality?
• Temporal consistency in B5 traits
• Evidence for consistency is strong—only became clear after B5 system was
introduced
Question:
• What role do genes play vs. environment in developing personality traits
Heritability
• Height weight movement cognitive factors all heritable
• First intuition: siblings are quite similar but if you ask whether siblings are
the same in personality then usually theyre quite different
• (Of course some are similar but in general extent to which siblings are
similar in personality is a lot less than physical traits)
Richard vs. Roland (Koester and his brother)
• Temperament: basic signs of personality—can tell in infancy
• Some kids are easier than others…
• Roland is more extraverted but theyre equal in openness, Koestner is higher
in agreeableness, Richard is lower in conscientiousness than Roland, Richard
is more Neurotic
• Richard was easy Roland was difficult
• Internal Locus of Control: Roland higher than Richard
• ^^There are other things besides the big 5, Locus of Control has to do with
our beliefs: how your behaviour relates to what happens, internal vs.
external (internal=strong contingency between what we do and outcome)
• Coming back to this later
Heritability quotient:
• An estimate of the proportion of variability in a given characteristic that can
be attributed to the genetic differences between people
• Used to refer to a population: 90% of variability of height is genetic
Methods of exploring heritability:
• Twin studies:
• Fraternal twins: dizygotic—only 50% shared genetics same as siblings, this is
75% of twins
• % of the time its monozygotic: share %
• Collect a lot of pairs of both types of twins you can compare
• Adoption studies:
• Adopted vs. biological kids: 0 vs. 50% genetic connection (expect biological
siblings to be more similar than adopted)
• Combined Adoption/twin studies:
• Identical twins raised together vs. apart
• If genetics is important: r will be higher for monozygotic vs. dizygotic
• Weird similarities between id twins (news clip)
find more resources at oneclass.com
find more resources at oneclass.com
Identical twins on the big 5
• N: MZ=.41 vs. DZ=.18
• E: M=.55 vs. D=.23
• O: M=.58 vs. D=.21
• A: M=.41 vs. D=.26
• C: M=.37 vs. D=.27
• Generally M is about twice D correlation
On Extraversion:
• In Sweden, US and Canada M were higher correlations than D
• Estimate: extraversion has heritability quotient of about 50%
• Strong… not as strong as physical… but strong
• So is it 50/50 nature/nurture?
• No:
• 1) Some of the variance is due to error
• 2) Environmental influence is two separate categories: shared vs. non-shared
Twins raised together vs. apart:
• Swedish twin study
• Raised with identical twin: correlation is .52, raised separately correlation is
.9… still very similar vs. DZ twins raised together=.9 vs. . for raised apart
• Nature vs. nurture… nature plays a B)G part.. nurture is small effect
• 10x more influence from genes than nurture
Other Personality Variables?
• Other than the B5
• Locus of Control:
• MZtogether: big 5=.47, locus of control=.28
• MZapart: big 5=.40, locus of control=.02 [SHOWS SIGNIFICANT DIFFERENCE
BETWEEN RAISED APART AND TOGETHER BUT NOT IN B5 ONLY IN LOC]
• DZtogether: B5=.19, LOC=.32
• DZapart: B5=.14, LOC=.08
• Locus of control is largely defined by environment not genetics…
• Again: is it 50/50?
• Seems wrong that genes would be so important
• 1:10 (e/g)
Pie chart for B5:
• 50% genetics
• 5% shared environment
• 20% error
• 25% is unspecified other than it coming from environment (not shared)
• E.g. Koestner wanted to be less neurotic—thought it had to do with parents
• But brother and sister were not neurotic and more outgoing… shared family
traits didnt
• Other choice: high school experience… sent to boarding school
• Differing non-shared environmental influence… more likely
• McAdams: birth order is one difference… not a shared factor
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Exploring genetic vs. family influences on personality: temporal consistency in b5 traits, evidence for consistency is strong only became clear after b5 system was introduced. Question: what role do genes play vs. environment in developing personality traits. Internal locus of control: roland higher than richard our beliefs: how your behaviour relates to what happens, internal vs. external (internal=strong contingency between what we do and outcome) 75% of twins siblings to be more similar than adopted: combined adoption/twin studies, weird similarities between id twins (news clip) If genetics is important: r will be higher for monozygotic vs. dizygotic. Identical twins on the big 5: n: mz=. 41 vs. dz=. 18, e: m=. 55 vs. d=. 23, o: m=. 58 vs. d=. 21, a: m=. 41 vs. d=. 26, c: m=. 37 vs. d=. 27, generally m is about twice d correlation. Other personality variables: other than the b5, locus of control, mztogether: big 5=. 47, locus of control=. 28, mzapart: big 5=. 40, locus of control=. 02 [shows significant difference.
