Story of Psychology - Morton Hunt [140]
It was a dazzling hypothesis, though Galton had only crude means of proving it. He sent a questionnaire to twins or relatives of twins he knew; he also asked them to give him the names of other twins. Eventually he had replies from ninety-four cases, eighty of which were of “close similarity” (probably identicals) and thirty-five of which provided enough details to be useful.
His report of the twin study is largely anecdotal; it tells of identicals who played tricks on people, or were both paddled by a schoolmaster who could not tell which one deserved punishment, of one who sometimes courted his brother’s fiancée, and so on. But when Galton sorted through his cases in search of identicals who became dissimilar in character, he found that, for some, “the resemblance of body and mind continued unaltered up to old age, notwithstanding very different conditions of life.” Others did exhibit differences, but in every case it was because an illness or accident had affected only one of the pair. In contrast, twins who had been dissimilar in childhood (probably fraternals), even if reared together and identically, did not become more alike over the years.12
Not one given to caution, Galton proclaimed, “There is no escape from the conclusion that nature prevails enormously over nurture when the differences of nurture do not exceed what is commonly to be found among persons of the same rank of society and in the same country.” From a contemporary perspective, the study was simplistic, imprecise, and far from conclusive. Still, it was a notable first, and the twin study method has been an important research strategy ever since and the most nearly definitive way of assessing the influences of heredity and environment on intelligence, personality traits, and other psychological characteristics.
Finally, Galton discussed in Inquiries his development of a number of mental tests in order quickly and simply to identify persons of superior intelligence, as part of his grand dream of improving the human race through eugenics. The year after Inquiries appeared, he began his trials of the tests at the International Health Exhibition, and when the fair closed down, he got permission from the South Kensington Museum to continue operating the laboratory there for a number of years. During that time he devised a number of new mental tests, among them a bar with a variable distance on it to test the ability to estimate extension, a rotating disk to test the ability to judge perpendicularity, sets of weights to be arranged in order of heaviness, and sets of bottles that contained aromatic material to be arranged according to intensity of odor.13
Galton was in his late sixties, far beyond the age at which scientists usually make their important discoveries, when he made his most important one. Appropriately, it involved his lifelong obsession, counting. Each kind of measurement made in the Anthropometric Laboratory had yielded a bell-shaped probability curve, but Galton sensed that he might glean other and highly significant information if he could discover how the different sets of measurements were related to one another. Some of the relationships were obvious—taller people, for instance, tended to weigh more—but what was the relationship between other sets of measurements? Which of them varied together and in the same degree? What did it mean if they did not vary in the same degree? Only by knowing how the data were related and which measures had little