Thomas Bouchard Jr., a psychologist at the University of Minnesota, was studying twins who had been raised apart. The Jims, he said, were almost certainly "the best case" of identical twins reared apart in the scientific literature.
The tests went far deeper than names. Their medical histories and brain-wave tests were almost identical, and so were their personality test results.
By 1987, the researchers had reached a conclusion. At least half of the twins' personalities, they said, were set by their genes, not by the homes they grew up in.