“Among mammals, for example, elephants live longer than rats...”
Then why do larger dog breeds have a shorter life span than those little yappy things?
Dogs are all the same species, with larger breeds of dog tending to experience more rapid aging due to greater food intake. Generally, lower food intake usually means that you live longer. Note that the rockfish study found longevity associated in part with modifications to insulin pathways. In spite of being essential to life, insulin causes metabolic stress that spurs aging.