The study suggests scientists may need to rethink which genes actually control aging. To understand this, the researchers fed fruit flies with antibiotics and monitored the lifetime activity of hundreds of genes that scientists have traditionally thought control aging. To their surprise, the antibiotics not only extended the lives of the flies but also dramatically changed the activity of many of these genes. Their results suggested that only about 30 percent of the genes traditionally associated with aging set an animal's internal clock while the rest reflect the body's response to bacteria. "For decades, scientists have been developing a hit list of common aging genes. These genes are thought to control the aging process throughout the animal kingdom, from worms to mice to humans," said Edward Giniger, from the NIH's National Institute of Neurological Disorders and Stroke.