Intelligence, Human
Intelligence, Human, a general term for what is often called mental alertness or versatility. It is the ability, or combination of abilities, that enables a person to do abstract thinking and to meet and solve a wide variety of new situations and problems. A person's intelligence is the intellectual ability that enables him or her to learn new information and skills and to solve problems.
Not all psychologists agree as to the nature of intelligence—whether it is a single ability or a group of several abilities. According to research by Louis L. Thurstone (1887–1955) and others, intelligence consists of specific factors, called primary mental abilities, plus a general factor common to the specific factors. The primary abilities include: verbal comprehension, word fluency, ability to handle spatial relationships, number ability, memorizing, perceptual ability, and reasoning.
To help them measure intelligence, psychologists have developed a variety of tests. Individuals range very widely in degree of intelligence as measured by such tests. At one extreme are the mentally gifted; at the other, persons classed as mentally retarded.
Psychologists agree that a person's intelligence level is determined by both heredity and environment, but they differ on the relative importance of these factors. Psychologists who believe the environmental factor is most important feel that intelligence-test scores reflect social, economic, and cultural influences in addition to innate ability; or that they reflect an unintentional but nevertheless built-in bias on the part of the tests (the tests, for example, might present situations or use a vocabulary familiar to American middle-class whites but foreign to inner-city blacks or Hispanic-Americans). They point out that there is evidence that compensatory education can raise test scores. Other psychologists contend that a person's innate ability limits improvement and argue that compensatory education, where it has been tried, has not been very successful.
In overall intelligence, men and women are equal. Women generally tend to test higher in verbal abilities, men in certain mechanical and spatial abilities.
Scores of intelligence tests that measure individuals from early age to their early 20's show a gradual increase in intelligence. Psychologists have conducted only a limited amount of research in adult intelligence, but it is believed that certain specific abilities may increase or decline after young adulthood. In old age there is often a decline in general mental ability.