Wells (2009 ) Thrift: a guide to thrifty genes, thrifty phenotypes and thrifty norms
International Journal of Obesity (2009) 33, 1331–1338.
There is a growing interest in evolutionary models of human adiposity, ‘thrifty genes’ or ‘thrifty phenotypes’, a variety of metabolic or behavioural traits which gives frugality in the expenditure or storage of energy.
At the broadest level, humans represent a thrifty species relative to other mammals, indicating that metabolic adaptations had a crucial role in the emergence of the Homo lineage, in particular in buffering reproduction from ecological stochasticity. Some variability in adiposity may be due to genotypes systematically favoured in certain ecological settings.
Genetic variability is also present within populations, and may be considered bet hedging (distributing risk across offspring to increase parental fitness). Bet hedging is an alternative to genetic drift to account for genetic variability in the absence of strong selective pressures. Contrasting with genetic variability emerging over the long-term, thrifty phenotypes represent a response to short-term ecological variability. Physiological plasticity allows the emergence of variability in response to ecological cues experienced directly or by very recent ancestors.
Cultural norms or individual preferences allow voluntary behavioural manipulation of thrift in individuals. Overall, there is a range of factors and processes both favouring and opposing thrifty genes, which may reflect moderate bet hedging rather than systematic adaptation. Plasticity protects the genome from selective pressures by tailoring the organism to ongoing ecological conditions. The fact that obesity can occur in different individuals through different genotypes, life histories and behaviours indicates that different treatments are also likely to be required.
- Martin Eastwood