Nature vs. Nurture in IQ Intelligence Powerpoint Presentation

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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



                                        1
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?


  Group A                     Group B
            Length                      Length

                              Width
  Width




                                                 2
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



                                          3
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


                                 4
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



                                                5
Genetic Influences
                1.0
Similarity of
 intelligence
                0.9                                                             The most
       scores   0.8                                                              genetically
(correlation)   0.7
                                                                                 similar
                                                                                 people
                0.6
                0.5
                0.4
                                                                                 have the
                0.3                                                              most
                0.2                                                              similar
                0.1                                                              scores
                0.0
                      Identical   Identical   Fraternal Siblings Unrelated
                      twins       twins       twins     reared   individuals
                      reared      reared      reared    together reared
                      together    apart       together           together




                                                                                  6
Family Influence on IQ

 Transient
  influence of
                       Identical twins
  family in which
  you are raised       Fraternal twins
  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
                             IQ   105
                         Scores
 Big increases in tests          100

  assessing fluid                  95
  intelligence, smallest           90
  in factual knowledge
 Increased schooling
                                   85

  only accounts for                80
  small portion of this            75
  increase
                                   70
 Due to changes in the             1910 1920 1930 1940 1950 1960 1970 1980 1990
  culture?                                              Year


                                                                 11
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


                                         12

				
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