ABSTRACT
Most striking and counter-intuitive are cases in which aging progresses in reverse. If we use the demographer’s definition of aging as mortality acceleration, then growth that leads to greater strength and lower mortality fits the definition of “negative senescence”. In most trees and some animals, mortality rates can decline over an extended time. Fertility also commonly increases as a plant or animal continues to grow larger. This may seem unexceptional to our intuition, because we think of it as a continuation of the growth to maturity; but it can be problematic for theories in which reproductive fitness is strictly maximized. There is a fitness bonus for early reproduction and so it is to be expected that natural selection favors a shift in reproduction to the earliest age that is physically possible.
