Individual Differences

Background and History

Individual differences in cognitive abilities have been studied since the 19th century, when Sir Francis Galton published Hereditary Genius, and they have continued to occupy the attention of psychologists, including Alfred Binet and David Wechsler, who produced some of the most widely used measures of intelligence. Individual differences in personality traits were studied conceptually by Gordon Allport and more empirically by Raymond Cattell and Hans Eysenck. Current views on individual differences in personality are dominated by the Five-Factor Model or Big Five.

[Page 473]Most individual differences are a matter of degree. Although it is convenient to talk about introverts and extraverts as if these were two distinct classes of people, in fact most people have some features of both introversion and extraversion and would fall near the middle of the distribution. Most traits are distributed in the familiar bell-shaped curve; there is little evidence for distinct types in psychology.

At any given time, people differ in their moods and their opinions of the weather. But the individual differences of greatest interest are those that reflect some enduring aspect of the individual. Both cognitive and personality traits meet this description. Longitudinal studies conducted over periods as long as several decades show that in adults, traits like verbal intelligence, emotional stability, and musical ability are exceptionally stable, with very gradual changes and high rank-order consistency. Young adults who are bright, unflappable, and tone-deaf are likely to be bright, unflappable, and tone-deaf 40 years later.

Several explanations have been offered for the stability of traits. For example, it is sometimes said that people build a life-structure that sustains their traits. The intellectually curious woman subscribes to magazines that continue to stimulate her curiosity and exercise her intellect. The sociable man acquires a circle of friends who reinforce his sociability. In addition, however, there is now compelling evidence from hundreds of studies that both cognitive and personality traits are substantially heritable, and the same genes that make one, say, suspicious at age 30 make one suspicious at age 70.

Ralph Waldo Emerson, the American transcendental philosopher, was dismayed by the evidence of trait consistency he saw, because it seemed to him to deprive people of freedom of will: “Temperament,” he wrote, “puts all divinity to rout.” But people generally embrace their own traits, recognizing them as integral parts of their identity. People might sometimes wish to be more assertive, organized, or imaginative, but in the long run, most accept their traits as their own authentic selves.

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