University of Sheffield
Department of Animal and Plan Sciences
Human Life-history group
Alfred Denny Building, Western Bank
Sheffield, S6 3JS
Abstracts (first author)
Genetic trade-offs and the evolution of human life-histories
Understanding life-history trade-offs is fundamental to explaining the diversity of life-history strategies in nature, and determining the genetic basis of trade-offs can identify how evolutionary constraint maintains life-history variation. Humans have evolved an unusual life-history compared to other primates, characterized by the menopause and long female post-reproductive lifespan (PRL). These have been hypothesized to evolve to enable (i) reduced reproduction when the costs of reproducing exceed the benefits, and (ii) enhanced grandchild survival. Previous tests of these hypotheses have examined phenotypic correlations between female reproductive rate and (i) PRL and (ii) offspring survival. However, environmental effects can mask genetic associations, and the direction and magnitude of these genetic correlations must be examined to determine the evolutionary potential of such traits. Using genealogical data from preindustrial Finnish church records for eight populations, we applied a multivariate quantitative genetic framework to examine the genetic basis of female reproductive rate, measured by inter-birth interval (IBI). We examined how additive genetic effects on IBI changed with age, and how age-specific genetic effects varied across environmental conditions. We determined the genetic trade-offs between IBI and both PRL and offspring survival, and how these trade-offs varied across ages and environments. Pilot analyses on four populations show a genetic basis to all traits, and suggest that genetic trade-offs between IBI and the other traits increased with age in poor environmental conditions, but were weak and age-independent in good conditions. IBI and PRL were positively related to lifetime fitness, suggesting that genetic trade-offs act as an evolutionary constraint. Our results will reveal new insight into human life-history evolution and generally highlight the fact that genetic correlations between traits may be age- and environment-dependent.
Testing evolutionary predictions of the Predictive Adaptive Response hypothesis in a pre-industrial human populationPDF
Environmental conditions during development can affect later-life health, but the evolutionary mechanisms underpinning these observations remain debated. The silver spoon (SS) hypothesis proposes that poor developmental conditions adversely affect development, leading to lower survival and fertility and increased metabolic disease risk, independent of later-life conditions. Meanwhile, the predictive adaptive response (PAR) hypothesis proposes that metabolic disease results from selection for development which is plastic with regard to environmental conditions, under which survival and fertility are maximised where conditions match in later life. If conditions change, metabolic disease results, but because the benefits of developmental plasticity exceed the costs, metabolic disease is not selected against. The observation that humans conceived during famine but raised in affluent conditions show later health problems is consistent with this idea. However, the proposed evolutionary mechanisms for putative developmental plasticity have rarely been empirically tested in humans. In particular, there are few studies examining the fitness consequences of conditions during development in varying later-life conditions. We tested the effects of early-life environmental conditions on later survival and fertility using data collected from several pre-industrial Finnish populations. We tested effects of early-life conditions on fitness during (i) varying later-life conditions, and (ii) adverse environmental conditions (a severe famine). Our results suggest that adverse early conditions decrease later fitness irrespective of later-life conditions, and that individuals born in poor conditions have lower survival and fertility during later-life famine. Our results do not support the PAR hypothesis, but are consistent with predictions of the SS hypothesis, which suggests that the early environmental conditions influence development in a manner which may persist into later life.