There are many ways to describe a person’s way of thinking: He can be artistic, creative, clever, or knowledgeable, or she can have a good memory. But to explain how well people can solve problems and understand the world around them, we use the term intelligence.

One widely accepted definition of intelligence was published in 1994 in an article called “Mainstream Science on Intelligence”:

A very general mental capability that, among other things, involves the ability to reason, plan, solve problems, think abstractly, comprehend complex ideas, learn quickly, and learn from experience. It is not merely book learning, a narrow academic skill, or test-taking smarts. Rather, it reflects a broader and deeper capability for comprehending our surroundings—“catching on,” “making sense” of things, or “ figuring out” what to do.

Researchers have argued about whether it’s possible to quantify intelligence. The most accepted way to do this is with an intelligence quotient (IQ) test that includes math and logic problems, memory and visual exercises, and questions about rearranged words or sentences. An average IQ score is 90 to 110, a score above 130 is considered superior intelligence, and a score below 70 indicates mental retardation. These tests have faced criticism, however, for being culturally biased and not allowing for multiple correct answers on subjective questions.

Because IQ tests measure not just the quantity of a person’s knowledge but also the ability to understand ideas, learning new information doesn’t necessarily increase your IQ. It may exercise your mind, however, which could help you develop greater cognitive skills. Overall, a person’s IQ does not tend to change much over the years.

High intelligence seems to run in families, although studies have not found specific genes that make much of an impact. It’s also been suggested that the ratio of body weight to brain volume, and the location of gray matter in the brain, might affect intelligence levels. Family upbringing seems to affect childhood IQ, but by late adolescence, this factor is less important: Adoptive siblings, once they’re grown, tend to show vastly different intelligence levels, while twins and other full siblings seem to be much closer in IQ.

ADDITIONAL FACTS

  1. In 1983, the psychologist Howard Gardner (1943–) defined several types of intelligence, including verbal, visual, physical, musical, mathematical, introspective, and interpersonal. Most standard definitions of intelligence do not factor in many of these traits.
  2. After the death of Albert Einstein (1879–1955), his brain was measured and found to be 15 percent wider than most human brains. It also contained abnormal-looking parietal lobes, which some theorize may have aided his mathematics skills.
  3. American Mensa, an “organization for smart people,” requires a score of 130 on the Stanford-Binet 5th edition IQ test to qualify for membership.