1Department of Evolutionary Genetics, Leibniz Institute for Zoo and Wildlife Research, Berlin, 2Wissenschaftskolleg zu Berlin, 3Department of Animal and Plant Sciences, University of Sheffield, UK, 4MRC Keneba, 5MRC International Nutrition Group, London School of Hygiene and Tropical Medicine, 6Department of Ecology and Evolutionary Biology, Yale University
Saturday 2:15-2:30, Ballroom B
Height and body mass index (BMI) are two anthropometric traits of importance in humans. They are related to survival and fecundity, and are heritable. Therefore, these traits are subject to selective pressures and evolve accordingly. This was true in our evolutionary past and still is today. However, our selective landscape has recently been profoundly affected by major demographic and environmental changes. In particular, the demographic transition (i.e. the universal trends in increasing survival and decreasing fecundity rate) results in a decrease in variance in relative fitness and so in the opportunity for selection to act on any traits. It also changes the composition of the variance in fitness from acting via variation in early survival to acting via variation in fecundity.
Here, we study how selection on height and BMI changed throughout a period of rapid demographic transition in rural Gambia 1956-2004. Our study relies on the longitudinal follow up of 3374 women resulting in 76,913 person-years observations derived from UK Medical Research Council data. We found that tallness was initially associated with increased early survival and decreased fertility, but these antagonistic effects on directional selection reduced with time, and stabilizing selection on height emerged. Directional selection for BMI initially favored high values but progressively switched to favor low values. These differences resulted from changes in fitness variance, together with direct changes in selective pressures triggered by environmental changes. Our results demonstrate how demographic and environmental trends encountered by current human populations worldwide can influence selection on anthropometric traits.