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---------------------------------------------------------------------------- Study finds environment more important than heredity in determining IQ ---------------------------------------------------------------------------- Copyright 1997 Nando.net Copyright 1997 The Associated Press NEW YORK (July 30, 1997 4:09 p.m. EDT) -- Nurture edges out nature in a new study of what determines a person's IQ. In an analysis combining more than 200 earlier studies, statisticians concluded that genes account for 48 percent of the factors that determine IQ. That's less than most psychologists would estimate, said study author Bernie Devlin, and far enough below the figure cited by the controversial 1994 book "The Bell Curve" to undercut its authors' main conclusions. "That number is way too small for their arguments to be of any great consequence," said Devlin, a professor of psychiatry at the University of Pittsburgh School of Medicine. Devlin's study, conducted with Michael Daniels and Kathryn Roeder of Pittsburgh's Carnegie Mellon University, also found that conditions during prenatal development significantly affect a person's intelligence. That suggests that inadequate prenatal care may explain why poorer people and blacks generally score lower on IQ tests. "Our study gives credence to that idea, and that in fact is something that people should be concerned about," Devlin said. "Poor prenatal care may have a negative impact on IQ." He and his colleagues report their findings in Thursday's issue of the journal "Nature." The statisticians combined the results of 212 earlier studies that compared the IQs of twins, siblings or parents and their children. Then the researchers constructed a set of statistical models, or predictions, to determine which one best fit the accumulated data. The best-fitting model was one that included genetic effects, environmental effects such as being raised in the same or different households and prenatal conditions. In twins, 20 percent of the similarity in IQ could be explained by the fact that twins share the same prenatal environment. Even for siblings who aren't twins, being carried by the same mother at different times explains 5 percent of the similarity in IQ. "The implication would be that the in-utero environment has a profound effect on IQ in the general population," said University of Minnesota psychologist Matt McGue. "It will stimulate people to think about prenatal factors in a way they hadn't before." It is already well-known that drinking or smoking during pregnancy can cause decreased IQ in children, and that exposure to lead in the womb can also lead to lower intelligence. There may be other prenatal factors that are important as well, Devlin said. McGue said the study casts doubt on the main hypothesis of "The Bell Curve." The book, by the late Harvard University professor Richard Herrnstein and political analyst Charles Murray, argues that the continued intermarriage of highly intelligent, well-educated people will lead to the development of a two-tiered American society -- one rich and smart, the other poor and dumb. But that can't come to pass, Devlin and his colleagues argue, because intelligence depends too little on genes. Even the 48 percent number overestimates the influence of a parent's "intelligence" genes, he explained, because in every person synergistic effects arise from the mixing of both parents' genes. Those synergistic effects account for about 14 percent of IQ, bringing the true inherited component down to 34 percent. "A lot of what was in "The Bell Curve" was premised on there being a high degree of parent-offspring resemblance in IQ," McGue said. "The parent-offspring degree of resemblance here may be modest." That may be, Murray countered in a telephone interview. But he argued that the book's conclusions are valid no matter how much of intelligence is genetic. "The big misconception about 'The Bell Curve' is that it's about genes. It's not. It's about the role of IQ in shaping social outcomes," he said. http://www.nando.net/newsroom/ntn/health/073097/health42_4987.html ---------------------------------------------------------------------------- [log in to unmask]