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Nature vs. Nurture in IQ

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Nature vs. Nurture in IQ – PowerPoint PPT presentation

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Title: Nature vs. Nurture in IQ


1
Nature vs. Nurture in IQ
  • Are differences between people due to
    environmental or genetic differences?
  • Misunderstanding the question
  • Is a persons intelligence due more to genes or
    to environment?
  • no genes no intelligence
  • both genes intelligence crucial for any trait

2
Nature vs. Nurture in IQ
  • Rectangle analogy
  • is a rectangles 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?

3
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

4
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

5
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

6
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

7
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?

8
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)

9
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

10
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?

11
Summary
  • Nature vs. nurture debate
  • heritability vs. environmentality
  • studies of twins family influence
  • Racial cultural differences in IQ
  • why we cant interpret differences as due to
    genetics
  • what we can attribute the differences to
  • Historical increase in IQ scores
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