even more questionable, she charged. "Magnify every problem in the IQ datatests, sampling bias, and so fortha hundredfold for the measurement of personality difference," she wrote, charging that the validity of all personality tests is open to question.
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Farber found in the twin literature reason to believe that environment played a substantial role in the formation of individual personalities. "Family influences show clearly in attitudes, values, choice of mate, and in presence of nonpsychotic psychiatric symptomatology. The cultural or regional influences transmitted by the family and social network also are present and probably show in general personality traits ranging from emotional expressivity to drinking habits . . . everything in these data points toward the massive and perhaps predominant influence of family and culture on attitudes and psychological traits."
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The paradox that Farber discovered, however, was that, as a group, "the more time MZ twins spend with no contact with each other, the more similar they seem to become," which directly counters the environmental argument advanced by Kamin. Early in the Minnesota study, Bouchard also got results indicating that separated twins were sometimes more similar than twins raised together. "You could argue that the twins reared together, because of the presence of each other, forced themselves apart. They differentiate. Whereas, if they were reared apart, they couldn't care less about this," he says. As the number of twins tested increased, however, this idea became harder to support. Bouchard now believes that twins reared apart and twins reared together are "about the same" in most measured tests. Separated twins who were separated later or who have spent more time together have no more difference in their IQs than those who were separated at birth and have practically never met.
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