title: A novel classification system for evolutionary aging theories.
abstract: Theories of lifespan evolution are a source of confusion amongst aging researchers. After a century of aging research the dispute over whether the aging process is active or passive persists and a comprehensive and universally accepted theoretical model remains elusive. Evolutionary aging theories primarily dispute whether the aging process is exclusively adapted to favor the kin or exclusively non-adapted to favor the individual. Interestingly, contradictory data and theories supporting both exclusively programmed and exclusively non-programmed theories continue to grow. However, this is a false dichotomy; natural selection favors traits resulting in efficient reproduction whether they benefit the individual or the kin. Thus, to understand the evolution of aging, first we must understand the environment-dependent balance between the advantages and disadvantages of extended lifespan in the process of spreading genes. As described by distinct theories, different niches and environmental conditions confer on extended lifespan a range of fitness values varying from highly beneficial to highly detrimental. Here, we considered the range of fitness values for extended lifespan and develop a fitness-based framework for categorizing existing theories. We show that all theories can be classified into four basic types: secondary (beneficial), maladaptive (neutral), assisted death (detrimental), and senemorphic aging (varying between beneficial to detrimental). We anticipate that this classification system will assist with understanding and interpreting aging/death by providing a way of considering theories as members of one of these classes rather than consideration of their individual details.
authors.affiliation: Heddle Initiative Research Unit, Advanced Science Institute Wako, Saitama, Japan ; Department of Investigative Pathology, Graduate School of Biomedical Sciences, Nagasaki University Nagasaki, Japan ; Department of Biological Sciences, Tokyo Metropolitan University Hachioji, Tokyo, Japan.
authors.forename: Lucas S
authors.initials: LS
authors.lastname: Trindade
authors.forename: Toshiro
authors.initials: T
authors.lastname: Aigaki
authors.forename: Alexandre A
authors.initials: AA
authors.lastname: Peixoto
authors.forename: Alex
authors.initials: A
authors.lastname: Balduino
authors.forename: Ivana B
authors.initials: IB
authors.lastname: Mânica da Cruz
authors.forename: Jonathan G
authors.initials: JG
authors.lastname: Heddle
keywords: altruism; caloric restriction; evolution; longevity; senemorphism; senescence