How metabolic rates influenced the evolution of human brain sizes
Species throughout time evolve based on their available metabolic energy versus their energy expenditure. An organisms’ metabolic energy (primarily a function of body size) must sustain the growth, reproduction and maintenance needs of the animal. For example, species that reproduce faster than expected for their body mass, generally have shorter maximum lifespans as their energy is directed towards reproductive function when compared to maintenance. Thus ultimately there are fundamental ‘’physiological trade-offs’’. Classically among primates this trade-off has been included in the need to grow and maintain large brains.
So how is it possible that humans, more than any other hominoid reproduce more often, and produce larger neonates and still have the longest lifespans and the largest, while also having the most metabolically costly brains?
It is from this perspective that humans present an energetic paradox. This article hypothesized that the human lineage experienced acceleration in metabolic rate, which provided energy for larger brains and faster reproduction without sacrificing maintenance and longevity. Measuring total energy expenditure (TEE) in adult chimpanzees (Pan troglodytes; n = 27), bonobos (Pan paniscus; n = 8), Western lowland gorillas (Gorillagorilla; n = 10) and orangutans (Pongo spp.; n = 11), and adult human samples (Homo sapiens; n = 141) the authors provide (very first time) evidence supporting the mechanism for the larger brains of Homo sapiens. The authors propose that a substantial increase in basal metabolic rate and body fat percentage, and changes in energy allocation was crucial in the evolution of human brain size and ultimately the history of life.
Kareemah Gamieldien (PhD, Physiology)
Cape Peninsula University of Technology
Herman Pontzer, Mary H. Brown, David A. Raichlen, et al. 2016. Metabolic acceleration and the evolution of human brain size and life history. Nature doi:10.1038/nature17654