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Heredity and Personality
Three truisms:
1. individuals differ in behavior
2. individuals differ in genetic makeup
3. individuals differ environmentally
Which causes individuals to differ in behavior?
Twin studies
1. Identical (MZ) twins reared together vs id. twins reared apart
- MZ twins share all their genes
Correlations Graph
- growing up in the same environment did not make MZ twins more
similar
- if family environment significantly shapes personality, MZ twins
reared together should be more similar than MZ twins reared apart
2. Identical – fraternal (DZ) twin comparison
Studies in Sweden, the U.S., and Britain:
- extraversion-introversion
- emotional maladjustment
- Swedish & British twins were adults
U.S. twins were adolescents
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- DZ twins were same sex
Correlations on Extraversion/Introversion and Neuroticism
- members of both kinds of twin pairs tend to be treated alike: shared
environment
3. Adoption Studies
- if environmental factors shape personality, adopted children should
show family resemblances to parents and siblings
Biological and Adoptive Correlations
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Conclusions
1. Genes appear to account for about one-half of personality variation
2. Few environmental influences are shared.
3. Growing up in the same family does not make people alike.
4. Personality theorists need to study environmental variables family
members do not share.
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"Exotic becomes Erotic" Theory of
Sexual Orientation (Bem, 1996)
- addresses the complexity of personality development
- combines many factors related to heredity and environment
Biological: genes and prenatal hormones produce children with particular
temperaments
- aggressive & active vs. more quietly sociable
Childhood society : beginning about age 5, boys and girls tend to play
separately
- rough and tumble for boys
- quieter play for girls
- some boys may choose to play with girls (and vice versa);
they will grow up around girls
- boys who grow up mainly around other boys will see girls as
"exotic"
- boys who grow up mainly around girls will see boys as exotic
Psychological: novel stimuli are physically arousing: heartrate and blood
pressure increase
- arousal is interpreted on the basis of environmental context
- in puberty, boys who grew up mainly with boys interpret
arousal at the novelty of girls as sexual arousal
- boys who grew up mainly with girls interpret arousal at the
novelty of boys as sexual arousal (and vice versa)
- the group seen as "exotic" becomes seen as erotically
stimulating
Evidence:
- 63% of gay men and lesbian women report not having enjoyed
typical activities for their gender when young
- true of only 10% of men and 15% of women who are heterosexual
- parallel trends in other precursors of sexual orientation
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- the theory addresses the complexity of the issues
- difficult to test
- study requirements:
- longitudinal
- children with different temperaments, activity preferences and
playmate groups
- track sexual orientation
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