Evolution of Thriftiness: An analytical viewpoint

We examine here, using a simple mathematical model, the conditions under which thrifty genes or fetal programming could evolve. Obesity and related disorders are thought to have their roots in metabolic thirftiness that evolved to combat periodic starvation. The failure to detect any thrifty genes and the association of low birth weight with type 2 diabetes, caused a shift in the concept from thrifty gene to thrifty phenotype and fetal programming. This hypothesis assumes that intra-uterine undernutrition programs the body to be thrifty, predicting and preparing for starvation in later life. However, there are reproductive costs associated with thriftiness. Results of the model suggest that under no condition thrifty and non-thrifty genes would co-exist stably in a population. The conditions for evolution of fetal programming are also very restricted. For species with longer life spans, programming for thriftiness is unlikely to evolve if starvation is decided by seasonality or stochastic annual climatic variations since the correlation between intra-uterine and life-time conditions is poor. On the other hand, if starvation is governed by longer periodicity factors such as population oscillations or social hierarchies, there can be better correlation between intra-uterine and life time conditions. Therefore social and population processes are more likely to have selected for fetal programming rather than seasonal and climatic “feast and famine” conditions. Since social and population processes can have cues other than diet, these cues may also influence the incidence of obesity related disorders as some recent evidence suggest