title: Testing evolutionary models of senescence: traditional approaches and future directions.
abstract: From an evolutionary perspective, the existence of senescence is a paradox. Why has senescence not been more effectively selected against given its associated decreases in Darwinian fitness? Why does senescence exist and how has it evolved? Three major theories offer explanations: (1) the theory of mutation accumulation suggested by PB Medawar; (2) the theory of antagonistic pleiotropy suggested by GC Williams; and (3) the disposable soma theory suggested by TBL Kirkwood. These three theories differ in the underlying causes of aging that they propose but are not mutually exclusive. This paper compares the specific biological predictions of each theory and discusses the methods and results of previous empirical tests. Lifespan is found to be the most frequently used estimate of senescence in evolutionary investigations. This measurement acts as a proxy for an individual's rate of senescence, but provides no information on an individual's senescent state or "biological age" throughout life. In the future, use of alternative longitudinal measures of senescence may facilitate investigation of previously neglected aspects of evolutionary models, such as intra- and inter-individual heterogeneity in the process of aging. DNA methylation data are newly proposed to measure biological aging and are suggested to be particularly useful for such investigations.
authors.affiliation: Department of Human Genetics, Box 110, Emory University School of Medicine, 615 Michael St. NE, Atlanta, GA, 30322, USA, crobi27@emory.edu.
authors.forename: Chloe
authors.initials: C
authors.lastname: Robins
authors.forename: Karen N
authors.initials: KN
authors.lastname: Conneely
mesh_terms: D000375:Aging / Q000235:genetics*; D000818:Animals; D005075:Biological Evolution; D019175:DNA Methylation; D044127:Epigenesis, Genetic; D058685:Genetic Pleiotropy; D014644:Genetic Variation; D006801:Humans; D008136:Longevity / Q000235:genetics; D008957:Models, Genetic; D059645:Mutation Rate; D013045:Species Specificity