Possible metabolic constraints on human brain weight at birth

Having humans born with adult-size brains would entail only a small and readily evolved increase in the size of the human female birth canal. The explanation for the present size of the human brain at birth is then plausibly based on the upper limit of brain that can be nourished by present human nutritional strategies. This limit turns out to be about 10% of the body weight of the newborn infant, in agreement with the actual value.