An Outline of the Phylogenetic History of Metazoan Aging Phenomenon(To the Study of Creating a Common Metazoa Aging Theory)

The phenomenon of aging in Metazoa has evolved from initially potentially immortal variants to forms ever more prone to aging. Potential immortality is an ancestral feature, which has been gradually lost during evolution, while aging and death by senescence are nonessential, yet very desirable, properties for the existence of the Metazoa with sexual reproduction, being a prerequisite for evolutionary progress, since, dur ing the stage of species establishment, this enhances the speciation processes accelerating the radiation of phylogenetic groups and gives remote evolutionary advantages—acceleration of both the evolution and the rate of replacement of one species by others. The main principle in the evolution of the aging phenomenon is substitution of external death factors of nonaging metazoans by internal death factors programmed in the genome. The aging mechanisms reduce to limitation of the repair and regeneration capacities of the adult phenotype and/or to complete or partial extermination of the stemcell pool. Aging is an integral process that cannot be reduced to one of the known cellular processes, which, in turn, cannot be an initial trigger of aging programmed in the genome in an implicit form (as there is no aging program per se): if disabling of the repair mechanism is genetically programmed at a certain stage of ontogenesis, this is actually the programming of the aging phenomenon. Mainly a complete or partial postmitotic design of an organism is programmed, and this, in turn, is a factor providing for “harmfulness” of the cellular mechanisms decreasing in an agedepen dent manner the physiological potential of an organism, thereby increasing the probability of Metazoa species dying. In general, the described data suggest that development of a general theory of aging in Metazoa does not require considerable addition to the database of biological science; however, a new understanding of the known facts is necessary, as this determines the initial cognitive position.