A new study of twins led by the University of Colorado Boulder shows that today's smokers are more strongly influenced by genetic factors than in the past and that the influence makes it more difficult for them to quit. "In the past, when smoking rates were higher, people smoked for a variety of reasons," said sociology Professor Fred Pampel, a study co-author. "Today the composition of the smoking population has changed. Smokers are more likely to be hard-core users who are most strongly influenced by genetic factors...

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