Genetic and Environmental Influences on Intelligence

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Genetic and Environmental Influences on
Intelligence
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Genetic Influences

• There does seem to be a heritable component of
  intelligence.
• Identical twins (same genes) have more highly
  correlated (similar) intelligence scores than
  fraternal twins (different genes)
  Genetic
• Identical twins raised together have more highly
  correlated scores than those raised apart
  Environmental

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Genetic Influences (continued)

• Variation in test scores attributable to genetic
  factors anywhere from 50 to 70.
• This means that we can attribute to heredity
  about 50 of the variation in intelligence within
  a group of people
• Cant say what percentage of an individuals
  intelligence is inherited!
• Also, remember that genes and environment
  interact in various ways.

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Environmental InfluencesEarly Intervention

• There is ample evidence that childrens
  environments have an impact on their
  intelligence, to an extent.
• There appears to be a sort of genetically
  determined range, and the environment affects
  where you fall in that range.
• E.g., kids in a very poor environment might fall
  at the lower end of their range.

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Group DifferencesEthnic Groups

• There are differences among racial groups on
  their intelligence test scores.
• The mean for one group is different than the mean
  for another group
• You can only make statements about an
  individuals intelligence if you know their score
  on a standardized intelligence test.
• In U.S., group mean for Asian-Americans is higher
  than for Caucasians, whose group mean is higher
  than that of African-Americans.

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Group DifferencesEthnic Groups

• The hotly debated issue is why are there ethnic
  group differences?
• Across countries and cultures, majority cultures
  as a group tend to outscore stigmatized minority
  groups.
• Even though variations between members of a group
  may reflect genetic differences (heredity), the
  average difference between groups may be due to
  the environment alone.

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Group DifferencesEthnic Groups

• The average intelligence score today exceeds the
  average intelligence score of the 1930s by about
  the same margin as the average white American
  outscores the average black American today.
• No one argues that the difference between today
  and the 1930s is genetic rather, it is related
  to the environment, people being better fed,
  better educated, etc.

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Group DifferencesGender

• There is no gender difference in overall
  intelligence scores.
• On achievement tests such as the SAT, males as a
  group tend to outscore females in the area of
  math problem-solving.
• Males as a group seem to have better spatial
  skills, ability to imagine 3-D images, etc.
• Females tend to have a stronger ability to detect
  emotions.
• Females also tend to be more verbally fluent.

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Bias in Testing?

• To determine if intelligence tests are biased,
  you have to define what type of bias you are
  talking about.
• Intelligence tests do detect not only innate
  differences, but those differences caused by
  differing cultural experiences.
• Often, when people ask if tests are biased, they
  are asking if the test is less valid for use with
  some groups than with others.

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Bias in Testing? (continued)

• In this sense, intelligence tests and other
  aptitude tests (like the SAT) are not biased
  they do not have better predictive validity for
  one group than for another.
• In other words, if an intelligence test score of
  95 or an SAT score of 900 predicts a C
  grade-point average, that prediction holds true
  across groups.

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Bias in Testing? (continued)

• In both testing and school performance, negative
  beliefs about ones performance can have a
  self-fulfilling prophecy effect.
• Research suggests that, if you believe that
  members of your group often do poorly (on testing
  or in class), you are less likely to succeed than
  if you believe that members of your group often
  do well.