Story of Psychology - Morton Hunt [222]
As Thomas and Chess watched some of the children develop to near adulthood, they were initially impressed by how often the temperament of a baby remained substantially unchanged in childhood and adolescence. Later, their more detailed findings led them to a more qualified conclusion. Frequently, some or many aspects of the basic temperament were modified by such major events as a serious accident or illness, or such changes in the environment as the death of a parent or a dramatic alteration in the family’s economic status. But when there were no such events or changes in the environment, the temperamental style of the first days of life was likely to be the temperamental style of the grown person.75
Even more impressive evidence that personality is partly innate has come from research in behavior genetics. This specialty, formerly somewhat outside mainstream psychology but now becoming more central to it, deals with genetic influences on psychological characteristics. Its major method of inquiry, originated by Galton, is to see to what extent people related to each other in differing degrees have similar mental abilities, personality, and achievements. First cousins have an eighth of their 25,000 to 30,000 genes in common, siblings a half, and identical twins all. If genes exert an influence on psychological development, the closer the genetic relationship between two people, the more psychologically alike they should be.
A vast amount of research conducted over the past half century has shown this to be the case. Some studies have shown that the closer the genetic relationship, the more alike the people are in mental health or illness.76 Others have found the same to be true of general intelligence and of specific mental abilities.77 And in the past three decades a number of geneticists and psychologists have found that the closer the genetic relationship, the more alike the personalities of the individuals.
Some of the personality research is based on analyses of the correlations in the traits of fraternal twins and of identical twins; consistently, the identicals are much more alike than the fraternals. Still, if they have been reared together in the same home, the evidence is less than perfect; they have had the same or very similar environmental influences all along (and identical twins, in particular, are even treated alike by their parents). For that reason, the best data—but the hardest to gather because instances are so rare—come from studies of identical twins separated at or soon after birth and raised in different homes and areas, where the environments are at least somewhat dissimilar.
Consider the case of Jim Lewis and Jim Springer, identical twins who were separated a month after their birth in 1940 and reared forty-five miles apart in different families in Ohio. They were totally unaware of each other’s existence until 1979, when they were thirty-nine. In that year they met, but not by accident. They had been tracked down by Professor Thomas Bouchard, director of the Minnesota Center for Twin and Adoption Research at the University of Minnesota, who was conducting a study of fraternals and identicals reared apart. Jim Lewis and Jim Springer, except for their clothing, were physically indistinguishable, as are almost all pairs of identicals. Remarkable as this always seems, what was far more remarkable were other similarities. Both men had wives named Betty, were heavy smokers of Salems, drove Chevrolets, bit their fingernails, and had dogs named Toy.
This sounds as if it had been concocted by a writer for one of those supermarket tabloids filled with accounts of such wonders as babies borne by eighty-year-olds. But the story was not concocted. Of course, some of the peculiar coincidences may have been due to the twins’ living in the same part of the country, others to chance. What was more important was the evidence adduced