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Biological Approaches. Kretschmer (1925) Sheldon (1942) Somatotype – degree of body type Endomorphy – plump, soft, Ectomorphy – slender, bookworms Mesomoprhs – muscular, large-boned. Sheldon’s research. 200 men, assessed personality and body type Found:

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Biological Approaches

Kretschmer (1925)

Sheldon (1942)

Somatotype – degree of body type

  • Endomorphy – plump, soft,

  • Ectomorphy – slender, bookworms

  • Mesomoprhs – muscular, large-boned


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Sheldon’s research

  • 200 men, assessed personality and body type

  • Found:

    endomorphs – relaxed, social, warm

    Mesomophs – competitive, bold, energetic, assertive

    Ectomorphs – restrained, inhibited, avoidant

  • Problems?


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Role of inheritance in personality

  • Behavioral genetics – study of genetic influences on behavioral qualities; also environmental influences

  • “Nature and Nurture”

    • Nature = genetics

    • Nurture = all environmental factors

      • Prenatal nutrition, exposure to drugs

      • Friends, neighborhood

      • Parenting, etc.


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Methods to study behavioral genetics

  • Selective Breeding

    • Thoroughbred horses – winners

    • Dog breeds

    • Mice – qualitatively different responses to alcohol


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Methods to study behavioral genetics cont’

  • Twin Studies

    • monozygotic twins – one egg is fertilized, then zygote splits into two, share same genetic material (MZ)

    • Dizygotic twins – two eggs are fertilized with separate sperm; share about 50%; same as siblings (DZ)

    • Can compare MZ & DZ twins raised separately and together

    • Heritability estimate = amount of variance accounted for by inheritance for the trait under study


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Twin Studies

  • Similarity in twins reared together is due to genes and environment

  • Similarity in twins reared apart is due to genes only because they don’t share experiences.

    Minnesota Twin Study

    8000 pairs to twins 1936 – 1955

    1200 pairs of twins 1971 – 1981

    8400 pairs of twins 1983 - 1990


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Twin Studies of personality

  • Estimates that 41% of individual differences in extraversion due to genetics

  • Estimates that 31% of individual differences in neuroticism due to genetics

  • Averaged personality: 30 – 50%


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Twin Studies

  • 40% of Big Five due to genetics

  • 25 % of Big Five due to nonshared environment

  • 25% of Big Five due to shared environment


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Twin Studies

**assumption: co-twins who are raised together experience similar environments

But MZ twins may be treated more similarly than DZ twins

Also, some separated twin pairs are raised by family members (i.e. overlap in environment?)


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Temperament

Buss & Plomin (1984)

Temperaments = inherited personality traits that are present early in childhood

  • activity level

  • Sociability

  • Emotionality

    Larsen & Diener (1985, 1987)

  • Impulsivity/aggression

    • Caution: possible rater bias

    • Good description of general style, but not strongly predictive of specific behaviors – probably need more specific traits


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Inhibited and uninhibited children are many similarities in what both genders seek in partners.  Both genders look for:

Kagan (1994, 1999)

high-reactive: crying, arching back, unhappy responsive to novel stimuli (20%)

low-reactive: calm to novel (40%)


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Aggression are many similarities in what both genders seek in partners.  Both genders look for:

  • Rushton, Fulker, Neale, Nias and Eysenck (1986)

    • 500+ MZ and DZ twin pairs

    • altruism, empathy, nurturance, assertiveness and aggressiveness and

    • found high correlations for MZ twins for each personality variable

    • Estimates of 50% heredity for aggression

    • Monozygotic twins were found to be more similar than dyzygotic twins on aggressiveness (for MZ twins, r = .40 and for DZ twins, r = .04).

    • nearly 50% of the variance for each personality variable was due to hereditary causes.


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Summary are many similarities in what both genders seek in partners.  Both genders look for:

  • Personality traits: MZ around .5, about .3 for DZ

  • Twin studies and FFM

  • Parallels between temperaments and FFM

  • Shared envinronment

  • Nonshared environment

    **importance of


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Interaction between genes and environment are many similarities in what both genders seek in partners.  Both genders look for:

  • Same environmental experience has different effects on individuals

  • Individuals with different genetic make-ups evoke different responses from the environment

  • Individuals with different genetic make-ups select and create different environment


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