The first person to try to develop a scientific intelligence test was Francis Galton. This British scientist, a half-cousin of English naturalist Charles Darwin, was a polymath, a person who is knowledgeable in many scientific areas. His interests included studying weather, fingerprints, and the peoples of Africa. Galton argued that plants and animals varied in systematic ways, and he devised new statistical methods for studying heredity. When it came to people, Galton proposed a controversial idea: the planned selection of superior parents as a means of improving the human race. To this end, he coined the term "eugenics" for the theoretical science of human breeding.
Before a practical program of eugenics could gain wide support, however, Galton had to show that his ideas were sound. Galton had been greatly influenced by his famous half-cousin's theory of evolution. A basic premise of that theory is that the variation among members of any species is inherited. The differences among parents in one generation are passed down to their offspring in the next generation.
In an 1869 book titled Hereditary Genius, Galton set out to show that high mental ability was passed down this way. It is likely that Galton's own family tree inspired this line of thinking, since both he and Darwin were grandsons of Erasmus Darwin, a noted physician and naturalist in his own right.
For the book, Galton picked a sample of people who had achieved great enough success in their careers to be listed in biographical reference works. Galton then researched their family backgrounds and found that about 10% had at least one close relative who was successful enough to be listed, too. Although this was a small percentage, it was still a much higher rate than would have been expected based on chance alone. This finding was consistent with Galton's theory of hereditary ability. It did not settle the issue, however, since most individuals in the same family share not only genes, but also similar lifestyles and experiences. Thus began the great nature-nurture debate, which asks: How much of people's intelligence is due to nature (the genes they inherited from their parents), and how much is due to nurture (the way they were raised and the experiences they have had)? This question continues to be hotly debated today.
In 1865, Galton suggested that a test might be devised to measure inherited differences in mental ability. When it came time to actually develop such a test, however, he was stumped. All he had was a vague notion that the inherited differences must arise from measurable differences within the brain and nervous system. Eventually, Galton developed a series of physiological tests for measuring reaction time, the sharpness of the senses, and physical energy. He hoped these tests would show the efficiency of a person's nervous system and, thus, the basis for his or her hereditary intelligence.
In 1884, Galton set up a laboratory at the South Kensington Museum in London to measure individual differences in mental ability. For a small fee, people could be tested there. Today, Galton's choice of tests seems amusingly misguided. For one test, he used a special whistle to measure the highest pitch people could hear. For another, he tested people's sensitivity to the smell of roses. Perhaps it is not surprising, then, that the tests did not work out as well as Galton had hoped. People with sharp senses and fast reaction times did not, as a group, turn out to especially gifted in other areas. Still, about 9,000 people paid for Galton's services, and scientists took note. If nothing else, Galton's laboratory was very successful at introducing the idea of intelligence testing to scientists and to the public.
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