View larger image | In a classic caloric restriction study, mice fed a normal amount died younger than those receiving 30 percent fewer calories (left). Older male mice given the drug rapamycin starting at 600 days of age (middle) and mice genetically engineered without a functional S6K1 protein (right), a crucial player in nutrient sensing and cell growth, also tended to live longer. Credit: Janel Kiley; Sources, from left: A. Bartke et al/Nature 2001; D. Harrison et al/Nature 2009; C. Selman et al/Science 2009