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Dietary restriction (DR) famously extends lifespan and reduces fecundity across a diverse range of species. A prominent hypothesis suggests that these life-history responses evolved as a survival-enhancing strategy whereby resources are redirected from reproduction to somatic maintenance, enabling organisms to weather periods of resource scarcity. We argue that this hypothesis is inconsistent with recent evidence and at odds with the ecology of natural populations. We consider a wealth of molecular, medical, and evolutionary research, and conclude that the lifespan extension effect of DR is likely to be a laboratory artifact: in contrast with captivity, most animals living in natural environments may fail to achieve lifespan extension under DR. What, then, is the evolutionary significance of the suite of responses that extend lifespan in the laboratory? We suggest that these responses represent a highly conserved nutrient recycling mechanism that enables organisms to maximize immediate reproductive output under conditions of resource scarcity.

The potential for sexual conflict to influence the evolution of life span and aging has been recognized for more than a decade, and recent work also suggests that variation in life span and aging can influence sexually antagonistic coevolution. However, empirical exploration of these ideas is only beginning. Here, we provide an overview of the ideas and evidence linking inter-and intralocus sexual conflicts with life span and aging. We aim to clarify the conceptual basis of this research program, examine the current state of knowledge, and suggest key questions for further investigation.S exual conflict arises because the sexes maximize their fitness via different, and often mutually incompatible, strategies, and its signature has been detected across a wide range of morphological, physiological, behavioral, and life-history traits in many species. A number of investigators have suggested that sexual conflict could play an important role in the evolution of two particularly interesting life-history traits: life span and aging (Svensson and Sheldon 1998;Promislow 2003;Bonduriansky et al. 2008;Maklakov and Lummaa 2013). Sexual conflict can affect life span and aging rate at both proximate (within-generation) and ultimate (evolutionary) scales. Sexually antagonistic behavioral or physiological interactions that increase mortality rate in one or both sexes (interlocus sexual conflict) could drive the evolution of faster life histories. Moreover, sex-specific optimization of reproductive strategies may often result in sex differences in life span and aging rates, and sexually antagonistic selection on shared genetic architecture can displace one or both sexes from their sex-specific optima for these traits (intralocus sexual conflict). Conversely, a change in life histories because of environmental fluctuations could affect the degree of sexual conflict in a population and influence sexual coevolution. Although evidence for sexual conflict is rapidly accumulating, our understanding of its relationship to life span and aging remains rudimentary. In this review, we provide a critical review of recent literature and highlight areas that require further investigation.

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