Genetics vs. Environment

1
Genetics vs. Environment

• Their Role in Intelligence

2
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.

3
Heredity and Environment

• Heritability
• The variation within a group caused by genetic
  factors
• 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

4
Twin Studies Family Influence Thomas Bouchard
the Minnesota Twins studies

• 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
Twin Studies
6
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
  influences
• 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.

7
Both genetics and environment have an effect on
IQ scores
8
Adoption Studies
Children's verbal ability scores became modestly
more like their biological parents' scores.
(Adapted from Plomin DeFries, 1998.)
9
Group Differences in Intelligence Test Scores
10
Group Differences in Testing

• A number of studies show scoring differences
  between different racial, ethnic, and gender
  groups.
• Are these differences due to nature or to
  nurture?
• Studies suggest environment is playing a heavy
  role.
• Heredity and environment interact to produce
  intelligence in individuals.

11
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
  to
• Spending more time in school
• More time doing homework
• Pressure and support from parents to achieve
  academically

12
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?

13
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)

14
Effects of Discrimination on Intelligence

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

15
Seed Analogy Argument for Environment
16
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
  groups.

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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
  Test
• Chitling Intelligence Test