Rhesus monkeys 27-year-old Canto, on a restricted diet (left), and 29-year-old Owen, a control subject on an unrestricted diet (right), were photographed at the Wisconsin National Primate Research Center at the University of Wisconsin-Madison on May 28, 2009. Canto and Owen were among the subjects in a pioneering long-term study of the links between diet and aging in rhesus macaque monkeys.