incidences, and the similarity of life events can be explained by the fact that identical twins are not just the sum of their individual genes but the product of many genetic constellations, which in a powerful, synergistic manner determine behavior, mannerisms, tics, social attitudes, marital relations, clothing choices, and political affiliations. Identical twins, in some respects, can be even more alike than we knew.
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The mountain of data compiled by the Minnesota team, along with ongoing twins research in Boulder, Stockholm, and Helsinki, stunningly tipped the balance in the nature-versus-nurture debate. Bouchard and his collaborators assessed a variety of personality characteristics, such as a sense of well-being, social dominance, alienation, aggression, and achievement, which they described in an important article in the 1988 Journal of Personality and Social Psychology . On the question of IQ, the Minnesota team found a higher correlation for separated MZ twins than most previous twin studies: 0.76, almost exactly the figure that Cyril Burt stood accused of fabricating. Identical twins reared together score 0.86, as much alike as the same person tested twice (0.87). In the personality domain, the Minnesota team attributed about half of the measurable variation to genetic causes. (These studies measure statistical differences within populations. They do not imply that fifty percent of any one individual's personality is genetically acquired.)
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Bouchard's team compared the personality scores for separated MZ twins and separated DZ twins against the scores for twins of both types who had been reared together. They concluded that identicals reared apart were about as much alike asin some cases more alike thanidenticals reared together. Moreover, there was not a single one of those personality traits in which fraternal
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