Nature vs nurture in iq
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Nature vs. Nurture in IQ Are differences between people due to environmental or genetic differences? Misunderstanding the question “Is a person’s intelligence due more to genes or to environment?” no genes = no intelligence both genes & intelligence crucial for any trait Group A Group B

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Nature vs. Nurture in IQ

  • Are differences between people due to environmental or genetic differences?

  • Misunderstanding the question

    • “Is a person’s intelligence due more to genes or to environment?”

    • no genes = no intelligence

    • both genes & intelligence crucial for any trait


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Group A

Group B

Length

Length

Width

Width

Nature vs. Nurture in IQ

  • Rectangle analogy

    • is a rectangle’s area due more to its width or its length?

    • are differences in area among rectangles due more to differences in their length or in their width?


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Heritability & Environmentality

  • Heritability

    • degree to which variation in trait stems from genetic, rather than environmental, differences among individuals

  • Environmentality

    • degree to which variation is due to environmental rather than genetic differences


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The Heritability Coefficient

  • Single number, ranging from 0 to 1.0

  • Represents amount of trait due to genetic differences

  • 0 means no variance due to genetics

  • 1 means all variance due to genetics

  • .30 means 30% is due to genetic differences, 70% due to environmental


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Twin Studies & Family Influence

  • If trait genetic:

    • closely related more similar than less closely related

  • Many close relatives share environments too

  • Types of studies to separate effects

    • monozygotic twins reared together

    • monozygotic twins reared apart

    • siblings/dizygotic reared together

    • siblings/dizygotic reared apart

    • adoptive siblings reared together


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Identical twins

Fraternal twins

Family Influence on IQ

  • Transient influence of family in which you are raised

    • adoptive siblings as children and adults

    • identical vs. fraternal twins reared together


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IQ Differences among Racial/Cultural Groups

  • Find differences among racial & cultural groups on IQ

    • American Blacks score about 15 points lower than Whites

  • WHY?

    • genetics?

      • Witty & Jenkins (1935)

      • No support for genetic differences

    • environment?


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IQ Differences among Racial/Cultural Groups

  • Each wheat field planted from same package of genetically diverse seeds

  • One field is quite fertile, the other is not

  • Within each field, differences due to genetics

  • Between each field, differences due to environment (fertility)


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Why differences between Blacks & Whites?

  • Social designation influences

    • autonomous minorities

      • deliberately separate themselves

    • immigrant minorities

      • came to country to better lives

      • see selves as better than those left behind

    • involuntary minorities

      • did not choose minority status

      • routinely judged as inferior by dominant majority

      • cross-cultural findings on IQ scores


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IQ

Scores

Year

Historical increase in IQ

  • Improved performance on IQ tests over the years

  • Big increases in tests assessing fluid intelligence, smallest in factual knowledge

  • Increased schooling only accounts for small portion of this increase

  • Due to changes in the culture?


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Summary

  • Nature vs. nurture debate

    • heritability vs. environmentality

    • studies of twins & family influence

  • Racial & cultural differences in IQ

    • why we can’t interpret differences as due to genetics

    • what we can attribute the differences to

  • Historical increase in IQ scores


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