Viscous populations evolve altruistic programmed aging in ability conflict in a changing environment
ABSTRACT Questions: Is aging evolutionarily adaptive? Can programmed aging widely evolve as altruism in viscous populations (i.e., widely distributed populations with limited offspring dispersal) in changing environment?
Features of Model: The model is individual-based. The probabilities of survival and reproduction are determined by abilities, and abilities increase with both inherited abilities and age-related abilities, so the old can survive and reproduce even if they are genetically less adapted to the environment (termed ‘ability conflict’). Inherited traits are determined by multiple independent loci; so active aging can enhance the local accumulation of adaptive inherited abilities in viscous populations.
Ranges of key variables: Dispersal varied from 0 (no dispersal) to 1 (global). The probability of environment-change during each calculation cycle varied from 0 to 1.
Conclusions: Altruistic aging evolves in structured viscous biological populations with ability conflict in a changing environment to allow the survival of genetically fitter young progenies. To evolve altruistic aging requires no more environmental change than does sex, suggesting that the generality of altruistic aging should be no less than sex in viscous populations. If selfish mutants appear only at low rates, higher-level selection would be stabilized even if the environment changes slowly. More extrinsic death can decrease aging rate (intrinsic death rate) to ensure the same expected lifespan in altruistic aging, providing testable predictions against traditional aging theories. My individual-based model also shows how traditional mathematical population genetics largely underestimated the prevalence of group selection.
Keywords: evolvability; genetic creativity; kin selection; longevity; population viscosity; senescence
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Jiangnan Yang firstname.lastname@example.org
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ABSTRACT: Why do individuals stop reproducing after a certain age, and how is this age determined? The antagonistic pleiotropy theory for the evolution of senescence predicts that increased early-life performance should be accompanied by earlier (or faster) senescence. Hence, an individual that has started to breed early should also lose its reproductive capacities early. We investigate here the relationship between age at first reproduction (AFR) and age at last reproduction (ALR) in a free-ranging mute swan (Cygnus olor) population monitored for 36 years. Using multivariate analyses on the longitudinal data, we show that both traits are strongly selected in opposite directions. Analysis of the phenotypic covariance between these characters shows that individuals vary in their inherent quality, such that some individuals have earlier AFR and later ALR than expected. Quantitative genetic pedigree analyses show that both traits possess additive genetic variance but also that AFR and ALR are positively genetically correlated. Hence, although both traits display heritable variation and are under opposing directional selection, their evolution is constrained by a strong evolutionary tradeoff. These results are consistent with the theory that increased early-life performance comes with faster senescence because of genetic tradeoffs.Proceedings of the National Academy of Sciences 05/2006; 103(17):6587-92. · 9.74 Impact Factor
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ABSTRACT: Medawar's 1952 paper 'An Unsolved Problem of Biology' underlies most subsequent theoretical work regarding the evolution of aging; it concludes that aging is accidental and could not have evolved; this prevents reconciling the growing body of evidence suggesting the existence of multiple, evolved, aging systems. The paper features a well-known thought experiment using test tubes to show why aging could not evolve. Medawar assumes that constant, random, breakage sufficiently represents lethal forces of nature; however, famine, drought, predation, disease, and accidents each uniquely affect populations. Predation is the only evolving force that continually invents new ways to kill members of the prey populations; thus all prey defenses to predation will eventually be defeated. Defenses to non-evolving or non-obligate lethal forces, however, should quickly evolve. Thus unevolving, identical test tubes cannot adequately represent biological populations. The example also ignores population booms and busts which often occur in nature. By ignoring these issues, Medawar examines only one population age distribution skewed towards younger individuals in predator-dominated environments while ignoring predator-free populations skewed towards older individuals after population crashes. Further, Medawar's test tubes lack meaningful competition for finite resources, and ignore declining fertility which occurs in all aging species. Medawar concludes that older individuals are too few in number to influence the population's gene pool for or against aging. This conclusion is found to be incorrect when variations in the age of reproductive senescence are introduced into a predator-free population.A new thought experiment with competing strains of algae corrects for these issues and shows that aging evolved and is retained so that groups retain enough genetic variability to allow for rapid evolution of a defense to novel predation. The example shows reasons why the rate of aging is directly linked to the reproductive rate, litter size, metabolic rate, reproductive senescence, and fixed body size. It also suggests that in the absence of predation, immortality would quickly evolve if not for the evolution of highly-conserved aging systems. Prior analysis of aging evolution is incorrect due to theorists' rejection of the idea of group selection. It is believed to be 'impossible' to select for mutations that are bad for the individual but good for the group. However, mutations that are neutral to young individuals which are only deleterious if expressed at older ages can accumulate in early-mortality, predator-dominated environments. Removing the predator allows deleterious mutation expression. Positive group selection then occurs amongst traits that are negative to the individual. Further, group selection is a universal force that occurs between local, non-breeding groups and not, as theorists propose, between distant groups of potentially interbreeding species. Local survivors migrate to replace extinct, related species. The antagonistic pleiotropy theory, which was created to salvage the idea of accidental aging, is examined and shown to be untenable. The hypothetical antagonistic pleiotropy genes that are beneficial to young while detrimental to old individuals, predicted to exist in the 1950s, are unlikely to exist, have not, and likely will not be found in sufficient quantity to participate in the aging process.Medical Hypotheses 03/2000; 54(2):326-39. · 1.05 Impact Factor
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ABSTRACT: Researchers are increasingly recognizing that social effects influence the evolution of aging. Kin selection theory provides a framework for analyzing such effects because an individual's longevity and mortality schedule may alter its inclusive fitness via effects on the fitness of relatives. Kin-selected effects on aging have been demonstrated both by models of intergenerational transfers of investment by caregivers and by spatially explicit population models with limited dispersal. They also underlie coevolution between the degree and form of sociality and patterns of aging. In this review I critically examine and synthesize theory and data concerning these processes. I propose a classification, stemming from kin selection theory, of social effects on aging and describe a hypothesis for kin-selected conflict over parental time of death in systems with resource inheritance. I conclude that systematically applying kin selection theory to the analysis of the evolution of aging adds considerably to ...12/2007; 38:103-128.