WASHINGTON (Reuters) - As Americans feasted on plates of Thanksgiving turkey Thursday, U.S. scientists reported they have made progress in understanding how eating less leads to longer life. Studies in yeast, rodents and other organisms have found that drastically cutting calories extends life span, and researchers are striving to find out how that happens. The hope is that human drugs may be developed to mimic that effect, without having to eat less. In a report in Friday's edition of the journal Science, researchers said studies with fruit flies, which have many genes similar to mammals, showed that an enzyme called...