N Non-evolutionary and Evolutionary Aging Theories Giacinto Libertini ASL NA2 Nord, Italian National Health Service, Frattamaggiore, Italy Department of Translational Medical Sciences, Federico II University, Naples, Italy Synonyms Evolutionary aging theories; Non-evolutionary aging theories; Programmed aging theories Definition The distinction in two groups of aging theories, non-evolutionary and evolutionary, derives from the non-consideration or consideration, respec- tively, of the evolutionism in the requirements of a theory. Here, this distinction is studied in depth. Moreover, it is observed that, within the group of evolutionary theories, some attribute, in evolutionary terms, always a negative value to aging and reach conclusions similar to those of non-evolutionary aging theories. On the con- trary, other theories attribute to aging a positive value in particular conditions and come to widely different conclusions. Overview Before the Darwinian hypothesis of evolution by natural selection (Darwin 1859), and also for a long time thereafter, aging has been considered by many theories as the inevitable effect of wear and tear phenomena and of the accumulation of harmful metabolic substances (Comfort 1979; Medvedev 1990). In the older theories of these group, which on the whole may be defined as “damage accumulation hypotheses” (Libertini 2015, p. 56), aging is explained as the effect of mechanical wear or of various types of biochem- ical damage (e.g., toxic metabolites, harmful sub- stances produced by intestinal bacteria, cosmic rays, mechanochemical deteriorations in cell col- loids) or of progressive tissue degeneration (e.g., changes in specific nervous/endocrine/vascular/ connective/other tissues and organs) (Comfort 1979; Medvedev 1990; Höhn et al. 2017; Ogrodnik et al. 2018). The newer hypotheses of this group propose that aging is caused by cumulative damage due to oxidative effects of free radicals on DNA/mitochondria/whole body or to DNA transcription errors (Libertini 2015). A different theory interpreted aging as a con- sequence of the cessation of somatic growth. In fact, while senescence is evident in animals that show somatic growth only up to a certain age, aging is not evident for species, as many fish, where there is constant capacity for growth (Bidder 1932): “[Bidder] pointed to a number of © Springer Nature Switzerland AG 2019 D. Gu, M. E. Dupre (eds.), Encyclopedia of Gerontology and Population Aging, https://doi.org/10.1007/978-3-319-69892-2_49-1