title: Fitness benefits of prolonged post-reproductive lifespan in women.
abstract: Most animals reproduce until they die, but in humans, females can survive long after ceasing reproduction. In theory, a prolonged post-reproductive lifespan will evolve when females can gain greater fitness by increasing the success of their offspring than by continuing to breed themselves. Although reproductive success is known to decline in old age, it is unknown whether women gain fitness by prolonging lifespan post-reproduction. Using complete multi-generational demographic records, we show that women with a prolonged post-reproductive lifespan have more grandchildren, and hence greater fitness, in pre-modern populations of both Finns and Canadians. This fitness benefit arises because post-reproductive mothers enhance the lifetime reproductive success of their offspring by allowing them to breed earlier, more frequently and more successfully. Finally, the fitness benefits of prolonged lifespan diminish as the reproductive output of offspring declines. This suggests that in female humans, selection for deferred ageing should wane when one's own offspring become post-reproductive and, correspondingly, we show that rates of female mortality accelerate as their offspring terminate reproduction.
authors.affiliation: Section of Ecology, Department of Biology, University of Turku, FIN-20014 Turku, Finland. mipayl@utu.fi
authors.forename: Mirkka
authors.initials: M
authors.lastname: Lahdenperä
authors.forename: Virpi
authors.initials: V
authors.lastname: Lummaa
authors.forename: Samuli
authors.initials: S
authors.lastname: Helle
authors.forename: Marc
authors.initials: M
authors.lastname: Tremblay
authors.forename: Andrew F
authors.initials: AF
authors.lastname: Russell
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D005075:Biological Evolution; D002170:Canada; D002648:Child; D002668:Child Rearing; D005260:Female; D005298:Fertility / Q000502:physiology; D005387:Finland; D006801:Humans; D016901:Intergenerational Relations; D008016:Life Change Events; D008017:Life Expectancy; D008136:Longevity / Q000502:physiology*; D008297:Male; D008425:Maternal Behavior; D008875:Middle Aged; D008954:Models, Biological; D009035:Mothers; D016487:Parenting; D017698:Postmenopause; D012098:Reproduction / Q000502:physiology*; D012641:Selection, Genetic; D016019:Survival Analysis; D013997:Time Factors