hamsters with circadian clock mutations can have free-running periods significantly below or above 24 hours. One such mutation results in a strain with an intrinsic circadian period of 22 hours. Compared to their wild-type counterparts these mutants have a shorter lifespan when living in a 24-hour world. Lesioning the suprachiasmatic nucleus of these animals actually prolonged their lives. This is a fascinating example of a situation in which part of the brain seems to be doing more harm than good.
