What Explains Differences In Intelligence?

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

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

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

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

Another Paradox Mean IQ scores for African Americans are about 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 that could be explained by genetic changes

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

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

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

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 increased average IQ lead to even more increases in IQ Differences between individuals are still explained largely by genetics

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

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

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

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?

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