title: No senescence despite declining selection pressure: Hamilton's result in broader perspective.
abstract: Theory predicts that senescence should inevitably evolve because selection pressure declines with age. Yet, data show that senescence is not a universal phenomenon. How can these observations peacefully coexist? Evolution of any trait hinges on its impact on fitness. A complete mathematical description of change in fitness, the total fitness differential, involves selection pressure along with a perturbation function that describes how the vital rates, mortality and fecundity, are affected across ages. We propose that the perturbation function can be used to model trade-offs when vital rates are perturbed in different directions and magnitude at different ages. We find that for every trade-off we can identify parameter values for which senescence does evolve and others for which it does not. We argue that this reconciles the apparent contradiction between data and theory. The total fitness differential is also instrumental in deriving mathematical relationships between alternative indicators of selection pressure. We show examples and highlight that any indicator combined with the right perturbation function can be used to parameterize a specific biological change. Biological considerations should motivate what perturbation functions are used. We interpret the relevance of Hamilton's finding that selection pressure declines for the evolution of senescence: declining selection pressure is a necessary but not a sufficient condition.
authors: Max Planck Research Group 'Modeling the Evolution of Aging', Max Planck Institute for Demographic Research, Konrad Zuse Straße 1, 18057 Rostock, Germany; Leyden Academy on Vitality and Ageing, Rijnsburgerweg 10, 2333 AA Leiden, The Netherlands. Electronic address: wensink@demogr.mpg.de.
authors: Maarten J
authors: MJ
authors: Wensink
authors: Max Planck Research Group 'Modeling the Evolution of Aging', Max Planck Institute for Demographic Research, Konrad Zuse Straße 1, 18057 Rostock, Germany.
authors: Tomasz F
authors: TF
authors: Wrycza
authors: Max Planck Research Group 'Modeling the Evolution of Aging', Max Planck Institute for Demographic Research, Konrad Zuse Straße 1, 18057 Rostock, Germany.
authors: Annette
authors: A
authors: Baudisch
mesh_terms: D000375:Aging / Q000502:physiology*; D008962:Models, Theoretical; D012641:Selection, Genetic
keywords: Evolution of aging; Fitness differential; Force of natural selection; Life history theory; Trade-offs