might lead to discoveries about ourselves that we are unwilling to make.
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In the mid-sixties, when Neubauer began his enquiry into the lives of separated twins, there were no major U.S. twin registries; now the University of Minnesota keeps track of more than 8,000 twin pairs; Virginia Commonwealth University operates the "Virginia 30,000," which follows 15,000 twin pairs plus their siblings, spouses, and parents; there are major registries in Kansas, California, and Kentucky, and smaller ones all over the country. The Veterans Administration maintains records of all twins who served in the Second World War and Vietnam. Pennsylvania State University, with several other institutions, oversees the Black Elderly Twin Study, which uses Medicare records to track down black twins throughout the United States. It is the only large-scale ethnic study in the country, but it may also become the largest study of genetics and aging among women in the world. In Holland, Denmark, Sweden, Norway, Finland, and Australia nearly every twin in the country has been identified. Moreover, in recent years, the technical analysis of twin studies has become increasingly sophisticated and subtle, often taking into account multiple environmental factors, non-twin relatives, and long-term observations. As a result of the variety and complexity of twin studies, along with powerful tools for analysis, the field of behavioral genetics has caused a revolution in the universities that has spilled into political life, reshaping the way our society views human nature and changing the terms of the debate about what government can and should do to improve the lives of its citizens.
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Much of the argument over individual differences in intelligence, for instance, arises from the variation between IQ test scores of identical and fraternal twins, the
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