Traditionally, psychologists have believed that intelligence is mostly a hereditary phenomenon -- in other words, how smart you are is determined by how smart your ancestors were, and your intelligence cannot change appreciably during your lifetime. Renowned paleontologist Stephan Jay Gould, in his book "The Mismeasure of Man," disputes the claim that intelligence is primarily hereditary. If intelligence is more susceptible to environmental influence than is commonly supposed, we miss opportunities to increase human intelligence due to ignorance of its origins.
Intelligence tests reveal racial differences -- the average IQ scores of some groups are higher than the averages of other groups. Nevertheless, individual scores differ far more widely than group averages, and geniuses appear in all races. Critics assert that the disparity in average IQ scores reflects not underlying intelligence but subtle racial bias based on prejudice and socioeconomic status. Racial disparities in average IQ scores are used to justify racially discriminatory social policies.
Once an individual's intelligence is reduced to a number, it becomes easier for educators to pigeonhole a student by labeling him "smart" or "dumb." These labels become self-fulfilling prophesies in two ways. First, "dumb" students are sometimes placed in remedial education classes, thereby denying them the opportunity to develop their intelligence. Second, if the "dumb" student is aware of his low I.Q. score, he may come to see himself as "dumb" and lose interest in educating himself.
Predictive validity refers to the ability of data to predict what happens in the future. In the case of IQ tests, predictive validity refers to the test's ability to predict later success in life. The predictive validity of the IQ test is not impressive. Child prodigies, for example, rarely grow up to be adult geniuses, while scientists with IQs in the average range have won the Nobel Prize. One possible explanation is that genius relies on personality traits as much as it relies on intelligence.