Primate energy input and the evolutionary transition to energy-dense diets in humans

Abstract

Humans and other large-brained hominins have been proposed to increase energy turnover during their evolutionary history. Such increased energy turnover is plausible, given the evolution of energy-rich diets, but requires empirical confirmation. Framing human energetics in a phylogenetic context, our meta-analysis of 17 wild non-human primate species shows that daily metabolizable energy input follows an allometric relationship with body mass where the allometric exponent for mass is 0.75+0.04, close to that reported for daily energy expenditure measured with doubly labelled water in primates. Human populations at subsistence level (n = 6) largely fall within the variation of primate species in the scaling of energy intake and therefore do not consume significantly more energy than predicted for a non-human primate of equivalent mass. By contrast, humans ingest a conspicuously lower mass of food (-64±6%) compared with primates and maintain their energy intake relatively more constantly across the year. We conclude that our hominin hunter–gatherer ancestors did not increase their energy turnover beyond the allometric relationship characterizing all primate species. The reduction in digestive costs due to consumption of a lower mass of high-quality food, as well as stabilization of energy supply, may have been important evolutionary steps enabling encephalization in the absence of significantly raised energy intakes.