RETRIEVAL PRACTICE Take a moment to answer each of these Learning Objective Questions (repeated here from within this section). Then click the 'show answer' button to check your answers. Research suggests that trying to answer these questions on your own will improve your long-term retention (McDaniel et al., 2009).

Studies of twins, family members, and adoptees indicate a significant hereditary contribution to intelligence scores. Intelligence seems to be polygenetic, and researchers are searching for genes that exert an influence. Heritability is the proportion of variation among individuals that can be attributed to genes.

Studies of twins, family members, and adoptees also provide evidence of environmental influences. Test scores of identical twins raised apart are slightly less similar (though still very highly correlated) than the scores of identical twins raised together. Studies of children raised in extremely impoverished environments with minimal social interaction indicate that life experiences can significantly influence intelligence test performance. No evidence supports the idea that normal, healthy children can be molded into geniuses by growing up in an exceptionally enriched environment.

Males and females tend to have the same average intelligence test scores, but they differ in some specific abilities. Girls are better spellers, more verbally fluent, better at locating objects, better at detecting emotions, and more sensitive to touch, taste, and color. Boys outperform girls at spatial ability and related mathematics, though in math computation and overall math performance, boys and girls hardly differ. Boys also outnumber girls at the low and high extremes of mental abilities. Evolutionary and cultural explanations have been proposed for these gender differences.

Racial and ethnic groups differ in their average intelligence test scores. The evidence suggests that environmental differences are responsible for these group differences.

Aptitude tests aim to predict how well a test-taker will perform in a given situation. So they are necessarily “biased” in the sense that they are sensitive to performance differences caused by cultural experience. By “inappropriately biased,” psychologists mean that a test predicts less accurately for one group than for another. In this sense, most experts consider the major aptitude tests unbiased. Stereotype threat, a self-confirming concern that one will be evaluated based on a negative stereotype, affects performance on all kinds of tests.