Is aging the price for memory?

Aging (senescence) is apparent in animals that possess long-lived postmitotic cells but is negligible in primitive species, such as hydras and other Cnidarians, all of whose cells are constantly renewed by cell division. This repetitive mitotic activity precludes the progressive intracellular accumulation of damaged biomolecules and organelles, which are obvious concomitants of aging in neurons and other long-lived cells of higher animals. We assume that the development of long-lived postmitotic cells, now found in the overwhelming majority of species, represented a useful evolutionary change. Probably, of particular importance was the evolution of long-lived neurons, which are required for long-term memory. However, the appearance of long-lived postmitotic cells not only increased fitness, but also gave rise to the aging process.