title: Evolution of longevity, age at last birth and sexual conflict with grandmothering.
abstract: We use a two-sex partial differential equation (PDE) model based on the Grandmother hypothesis. We build on an earlier model by Kim et al. (2014) by allowing for evolution in both longevity and age at last birth, and also assuming that post-fertile females support only their daughters' fertility. Similarly to Kim et al. (2014), we find that only two locally stable equilibria exist: one corresponding to great ape-like longevities and the other corresponding to hunter-gatherer longevities. Our results show that grandmothering enables the transition between these two equilibria, without extending the end of fertility. Moreover, sensitivity analyses of the model show that male competition, arising from a skew in the mating sex ratio towards males, plays a significant role in determining whether the transition from great ape-like longevities to higher longevities is possible and the equilibrium value of the average adult lifespan. Whereas grandmothering effects have a significant impact on the equilibrium value of the average age at last birth and enable the transition to higher longevities, they have an insignificant impact on the equilibrium value of the average adult lifespan.
authors.affiliation: School of Mathematics and Statistics, University of Sydney, NSW 2006, Australia. Electronic address: M.Chan@maths.usyd.edu.au.
authors.forename: Matthew H
authors.initials: MH
authors.lastname: Chan
authors.affiliation: Department of Anthropology, University of Utah, Salt Lake City, UT 84112, USA. Electronic address: Hawkes@anthro.utah.edu.
authors.forename: Kristen
authors.initials: K
authors.lastname: Hawkes
authors.affiliation: School of Mathematics and Statistics, University of Sydney, NSW 2006, Australia. Electronic address: PKim@maths.usyd.edu.au.
authors.forename: Peter S
authors.initials: PS
authors.lastname: Kim
mesh_terms: D000328:Adult; D000367:Age Factors; D005075:Biological Evolution; D005260:Female; D005298:Fertility; D000066502:Grandparents; D006801:Humans; D008136:Longevity / Q000502:physiology*; D008297:Male; D008954:Models, Biological; D009026:Mortality; D009154:Mutation; D036801:Parturition; D012098:Reproduction; D012725:Sexual Behavior; D013997:Time Factors
keywords: Evolutionary dynamics; Grandmother hypothesis; Population dynamics; Postmenopausal longevity