What Explains Differences In Intelligence?

1. What Explains Differences In Intelligence?

2. Thesis • A large portion of differences in IQ scores can be explained by environmental differences even though there is a substantial genetic component

3. About IQ • IQ scores are not the same thing as intelligence • They are estimates of intelligence based on a particular way of defining it and a particular standardized test

4. How is Intelligence Measured? • Standardized Intelligence Tests • WAIS • Stanford-Binet • Examples of subtests • Digit span • Picture arrangement • Information

5. A Paradox About IQ • IQ scores keep going up • Flynn Effect • Average IQ in U.S. increased about 22 points between 1932 and 2002 • Behavioral genetics research shows that IQ is highly heritable • The increases in IQ happened too quickly to be explained by genetic changes

6. Another Paradox • Mean IQ scores for African Americans are about 10-15 points lower than for European Americans • The environments would have to be extraordinarily dissimilar to account for the difference • The difference is decreasing more rapidly than could be explained by genetic changes

7. Genetic Influence • Twin studies • Identical twins who are adopted and reared apart share all of their genes but not their environments • Fraternal twins or siblings who are adopted and reared about share only half of their genes

8. Is Intelligence Genetic? • The genetic contribution depends on differences in environments • For individuals in similar environments, much of the variability is explained by genetics

9. Resolving the Paradox • In the real world, genetic and environmental influences are not separate • Genetic influences can cause environmental differences, which then cause differences in the trait (e.g., IQ) • These influences are counted as genetic but they are also environmental

10. Social Multipliers • Social changes can cause rapid changes in a trait • These changes (e.g., increases in IQ) create a need for individuals to keep up • Changes in environment that increase average IQ lead to even more increases in IQ • Differences between individuals are still explained largely by genetics

11. Examples of Social Multipliers • Smaller families, leading to more time to talk with children about abstract issues • More leisure time, leading to more mentally challenging leisure activities • Technology, leading to less emphasis on rote learning and more emphasis on problem solving

12. What About the Race Issue? • Reliable group differences in IQ scores • Greater variability within groups than between groups • These group differences can’t be accounted for by test bias

13. What About the Race Issue? • Racial groups are defined sociologically, not biologically • Twin studies show that individual differences in IQ are heritable, not that group differences are heritable

14. What About the Race Issue? • Recall that the changes in group IQ differences can’t be explained by genetic changes • Could differences in social multipliers account for the group differences in IQ?

15. A Few Cautions About IQ • An IQ score is an estimate • Intelligence is defined culturally • IQ scores are predictive of measures of success, but this may be a self-fulfilling prophecy