Diet and Brain Evolution: Nutritional Implications of Large Human Brain Size

Abstract

The evolution of large human brain size has had important implications for the nutritional biology of our species. Relative to other primates and other mammals, humans spend much larger share of their resting energy budget on brain metabolism. The high energy costs of our brains are supported by the consumption of diets that are high in quality, that is, relatively rich in energy and fat. Among living primates, relative brain size is positively correlated with dietary quality. Humans fall at the positive extreme for both parameters, having the largest relative brain size and the highest quality diet. High levels of encephalization in humans also have important implications for early childhood growth and development. Human infants have much higher levels of body fatness than those of other mammals. These greater levels of adiposity provide a supply of stored energy to accommodate the high metabolic demands of rapid brain growth. Under conditions of nutritional stress, human infants preserve body fat for brain metabolism by reducing rates of linear growth and decreasing levels of fat oxidation. The human fossil record indicates that major changes in both brain size and diet quality occurred in association with the emergence of the genus Homo between 2.0 and 1.7 million years ago in Africa. With the evolution of Homo erectus at 1.8 million years ago, we find evidence of an important adaptive shift – major increases in brain size and body size, along with the emergence of the first hunting and gathering economy. While dietary change was not the prime force responsible for the evolution of large human brain size, improvements in dietary quality and increased consumption of dietary fat appear to have been a necessary condition for promoting encephalization in the human lineage. Further research is needed to better understand the nature of the dietary changes that took place with emergence of early human ancestors.