Energetics and the evolution of human brain size

The brain is a costly organ to run in terms of energy supply, so how do humans accommodate brains that are so much larger than those of comparable primates without any apparent difficulty? A widely held explanation is the expensive-tissue hypothesis, which proposes a trade-off between brain size and the mass of other energetically expensive organs, especially the digestive tract. Now a survey of 100 mammal species reveals no such trade-off, refuting the idea that expensive tissues compete for energy. There is a negative correlation between the size of brains and the amount of stored energy in the form of adipose tissue, however. The authors propose that the increase in human brain size was facilitated by a combination of stabilization of energy inputs and a redirection of energy from locomotion, growth and reproduction.