Human evolution in modern societies: A shifting trade-off model


Philipp Mitteröcker

Unit for Theoretical Biology, Department of Evolutionary Biology

University of Vienna

Throughout human history, cultural transitions repeatedly altered human lifestyle, the conditions of survival and reproduction as well as the modes of biocultural inheritance. Cultural changes thus have been important drivers of biological evolution in our species. With the advancement of agriculture, housing, medicine, and other technologies, natural selection has been continually reduced. It is thus tempting to assume that biological evolution in humans has reduced or even stopped as a result of continually reduced natural selection. I will show that this is not true: by shifting existing fitness trade-offs, reduced selection pressures have even triggered new evolutionary changes. Many anatomical, physiological, and behavioral traits have evolved by trading off fitness for different functions, life stages, or environmental conditions. The resulting “evolutionary compromises” optimize average fitness in a population and may also entail individuals that appear to be maladapted for one or more of the involved functions. Relaxation of one of the opposed selective forces, e.g. by technological or medical advancements, disrupts the evolved equilibrium and induces a novel evolutionary trend. I will outline this theory and illustrate it with examples from childbirth and immune function. Extending the model to trade-offs between ecological and social selection, I will use global demographic and biometric data to demonstrate how relaxed ecological selection throughout the last centuries has affected the pattern of sexual dimorphism in human body height. Finally, I will briefly discuss ethical and political challenges involved in this research.