ONCE THE brain’s true purpose was ascertained, scientists began finding new ways to observe it and its functions. Starting with noninvasive methods, like IQ tests, they tried to learn more about the living brain and measure how it worked. These intelligence tests painted a picture of how the brain collected information, processed it, and then made conclusions.

CT scans open windows into the brain's interior structure.
CT scans open windows into the brain’s interior structure.

Peering inside a living brain was virtually impossible-most of what scientists knew abour the brain’s anatomy was based on autopsies. But in the late 19th century, the invention of the x-ray made it possible to take a look inside the skull. In the 20th century, new scanning methods came along and gave greater insight into how the living brain works.


ALFRED BINET (1857-1911) made the first serious effort to chart intelligence. In 1905, France commissioned him to create a test to identify students whose intelligence was below average. Binet and his doctoral student, Theodore Simon, devised a series of tasks for children. They then tested how well children of various ages performed the tasks, which gradually increased in complexity. Their work led them to create a scale of normal mental functioning. Binet’s intelligence scores compared a child’s mental abilities with those of h is or her peer group. The test has been updated many times.

A 1937 Stanford-Binet intelligence test includes miniatures and printed matter.
A 1937 Stanford-Binet intelligence test includes miniatures and printed matter.

During World War II, the American government gave Army recruits intelligence tests to screen them for war work. Plenty of other groups have been given IQ tests since then, allover the world. If you look only at their scores, you might think humans are getting smarter all the time. New Zealand political scientist James R. Flynn observed that standardized intelligence test scores from 20 countries historically have kept rising by about three points a decade. The reason isn’t entirely clear, but it’s possible that improvements in nutrition, coupled with the more stimulating environments in which children are raised, contribute to greater neuronal complexity.

Today, scientists still wrestle not only with what intelligence is, but also how it can be measured. Harvard University’s Howard Gardner believes at least seven types of intelligence exist, from the mathematical to the athletic.

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