3 Feral


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  • Clearly, IQ is not the only psychological construct for which this debate applies, and instructors may wish to take a moment to name the other areas (i.e., personality, mental disorders, etc.) for which heritability is hotly debated.
  • 3 Feral

    1. 1. Nature vs. Nurture in IQ <ul><li>Are differences between people due to environmental or genetic differences? </li></ul><ul><li>Misunderstanding the question </li></ul><ul><ul><li>“ Is a person’s intelligence due more to genes or to environment?” </li></ul></ul><ul><ul><li>no genes = no intelligence </li></ul></ul><ul><ul><li>both genes & intelligence crucial for any trait </li></ul></ul>
    2. 2. Nature vs. Nurture in IQ <ul><li>Rectangle analogy </li></ul><ul><ul><li>is a rectangle’s area due more to its width or its length? </li></ul></ul><ul><ul><li>are differences in area among rectangles due more to differences in their length or in their width? </li></ul></ul>Group A Group B Length Width Length Width
    3. 3. Heritability & Environmentality <ul><li>Heritability </li></ul><ul><ul><li>degree to which variation in trait stems from genetic, rather than environmental, differences among individuals </li></ul></ul><ul><li>Environmentality </li></ul><ul><ul><li>degree to which variation is due to environmental rather than genetic differences </li></ul></ul>
    4. 4. The Heritability Coefficient <ul><li>Single number, ranging from 0 to 1.0 </li></ul><ul><li>Represents amount of trait due to genetic differences </li></ul><ul><li>0 means no variance due to genetics </li></ul><ul><li>1 means all variance due to genetics </li></ul><ul><li>.30 means 30% is due to genetic differences, 70% due to environmental </li></ul>
    5. 5. Twin Studies & Family Influence <ul><li>If trait genetic: </li></ul><ul><ul><li>closely related more similar than less closely related </li></ul></ul><ul><li>Many close relatives share environments too </li></ul><ul><li>Types of studies to separate effects </li></ul><ul><ul><li>monozygotic twins reared together </li></ul></ul><ul><ul><li>monozygotic twins reared apart </li></ul></ul><ul><ul><li>siblings/dizygotic reared together </li></ul></ul><ul><ul><li>siblings/dizygotic reared apart </li></ul></ul><ul><ul><li>adoptive siblings reared together </li></ul></ul>
    6. 6. Family Influence on IQ <ul><li>Transient influence of family in which you are raised </li></ul><ul><ul><li>adoptive siblings as children and adults </li></ul></ul><ul><ul><li>identical vs. fraternal twins reared together </li></ul></ul>Fraternal twins Identical twins
    7. 7. IQ Differences among Racial/Cultural Groups <ul><li>Find differences among racial & cultural groups on IQ </li></ul><ul><ul><li>American Blacks score about 15 points lower than Whites </li></ul></ul><ul><li>WHY? </li></ul><ul><ul><li>genetics? </li></ul></ul><ul><ul><ul><li>Witty & Jenkins (1935) </li></ul></ul></ul><ul><ul><ul><li>No support for genetic differences </li></ul></ul></ul><ul><ul><li>environment? </li></ul></ul>
    8. 8. IQ Differences among Racial/Cultural Groups <ul><li>Each wheat field planted from same package of genetically diverse seeds </li></ul><ul><li>One field is quite fertile, the other is not </li></ul><ul><li>Within each field, differences due to genetics </li></ul><ul><li>Between each field, differences due to environment (fertility) </li></ul>
    9. 9. Why differences between Blacks & Whites? <ul><li>Social designation influences </li></ul><ul><ul><li>autonomous minorities </li></ul></ul><ul><ul><ul><li>deliberately separate themselves </li></ul></ul></ul><ul><ul><li>immigrant minorities </li></ul></ul><ul><ul><ul><li>came to country to better lives </li></ul></ul></ul><ul><ul><ul><li>see selves as better than those left behind </li></ul></ul></ul><ul><ul><li>involuntary minorities </li></ul></ul><ul><ul><ul><li>did not choose minority status </li></ul></ul></ul><ul><ul><ul><li>routinely judged as inferior by dominant majority </li></ul></ul></ul><ul><ul><ul><li>cross-cultural findings on IQ scores </li></ul></ul></ul>
    10. 10. Historical increase in IQ <ul><li>Improved performance on IQ tests over the years </li></ul><ul><li>Big increases in tests assessing fluid intelligence, smallest in factual knowledge </li></ul><ul><li>Increased schooling only accounts for small portion of this increase </li></ul><ul><li>Due to c hanges in the culture? </li></ul>Year IQ Scores
    11. 11. Summary <ul><li>Nature vs. nurture debate </li></ul><ul><ul><li>heritability vs. environmentality </li></ul></ul><ul><ul><li>studies of twins & family influence </li></ul></ul><ul><li>Racial & cultural differences in IQ </li></ul><ul><ul><li>why we can’t interpret differences as due to genetics </li></ul></ul><ul><ul><li>what we can attribute the differences to </li></ul></ul><ul><li>Historical increase in IQ scores </li></ul>