Animals on the early branches of the tree of life, such as jellyfish and sea sponges, defy the usual conventions of aging. Some show abilities to regenerate damaged or missing tissues, halt or reverse aging, and in the case of at least one jellyfish species show a form of "immortality." A new study from researchers at the University of California, Davis, and Harvard Medical School takes a detailed look at a group of proteins called sirtuins, linked to protection against cellular injury and aging, in these animals and across the rest of the animal kingdom. The work was published Sept. 6 in Molecular Biology and Evolution.