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Genetics vs. Environment


Genetics vs. Environment Their Role in Intelligence Nature vs. Nurture in IQ Is a person s intelligence due more to genes or to environment? – PowerPoint PPT presentation

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Title: Genetics vs. Environment

Genetics vs. Environment
  • Their Role in Intelligence

Nature vs. Nurture in IQ
  • Is a persons intelligence due more to genes or
    to environment?
  • Both genes intelligence crucial for any trait
  • Environmental factors determines which genes get
    switched on.
  • Example of nutrition effecting you reaching your
    genetic potential in height.

Heredity and Environment
  • Heritability
  • The variation within a group caused by genetic
  • Thought to be about 50
  • Environment
  • Degree to which variation is due to environmental
    rather than genetic differences
  • Environmental Factors can be early intervention,
    schooling and family life

Twin Studies Family Influence Thomas Bouchard
the Minnesota Twins studies
  • If trait genetic
  • closely related more similar than less closely
  • 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

Twin Studies
Data Analysis
  • The data show that both genetics and environment
    have an effect on IQ scores.
  • The more closely two individuals are related
    genetically, the more similar their IQ scores
  • Identical twins reared together are more alike
    than are fraternal twins reared together.
  • Also show the importance of environmental
  • Identical twins reared together are more alike
    than are identical twins reared apart
  • siblings who are reared together are more alike
    than are siblings reared in different homes.

Both genetics and environment have an effect on
IQ scores
Adoption Studies
Children's verbal ability scores became modestly
more like their biological parents' scores.
(Adapted from Plomin DeFries, 1998.)
Group Differences in Intelligence Test Scores
Group Differences in Testing
  • A number of studies show scoring differences
    between different racial, ethnic, and gender
  • Are these differences due to nature or to
  • Studies suggest environment is playing a heavy
  • Heredity and environment interact to produce
    intelligence in individuals.

Why do Japanese and Chinese students perform
better than Americans on intelligence and
achievement tests?
  • They score the same before school but once school
    starts they begin to show more gains. This due
  • Spending more time in school
  • More time doing homework
  • Pressure and support from parents to achieve

Group DifferencesAustralian aborigine white
scores on IQ tests
  • Play Intelligence and Culture (402) Module 4
    from The Brain Teaching Modules (2nd edition).
  • Are the differences in scores the result of
    environment or genes?
  • Which theory of intelligence does this example
    prove? Gardners Multiple Intelligences or
    Spearmans g factor?

Racial Difference in IQ
  • Racial difference in average IQ among different
    racial groups can be measured
  • More variation in IQ scores within a particular
    group than between groups
  • Stereotype Threat When members of a particular
    group fear they are being thought of or evaluated
    according to a negative stereotype, they fear
    that they may confirm the stereotype leading to
    self-doubt and anxiety resulting in poor
    performance. (see Box 7.4 on pg. 311)

Effects of Discrimination on Intelligence
  • Burakumin people of Japan are severely
    discriminated against.
  • Despite being genetically similar to Japanese
  • Their IQ scores are 10 to 15 points lower than
    normal Japanese people.

Seed Analogy Argument for Environment
Within and Between Group Differences
  • Each corn 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)
  • Unless the environments of two racial groups are
    totally identical, it is impossible to estimate
    the overall genetic differences between the two

(No Transcript)
Are IQ Tests Culturally Biased?
  • If IQ test reflects white, middle-class cultural
    knowledge and values it could result in poor
    scores by minorities.
  • Test will favor the people from the culture in
    which it was developed.
  • Factors like test-taking behavior, motivation,
    attitudes towards the test and previous
    experiences with tests can affect performance.
  • Try some culturally biased tests yourself
  • Robert Williams IQ Test the Dove Counterbalance
  • Chitling Intelligence Test