A central role for dietary sugars in human evolution

What did our ancestors eat? Current understanding of diet in human evolution is predicated on abundant animal foods and mastery of fire, both unlikely for early hominins. Using multiple lines of evidence, including the metabolic requirements of an enlarging brain and reproduction, we model macronutrient distribution across 4 million years of evolution. Before cooking made starch easily digestible, the sugars in fruit and honey provided glucose, the brain's preferred fuel. Modeling suggests that sugars provided >25% of dietary energy, fulfilling obligatory glucose demand. Pounding and cooking released glucose specifically, not merely energy. The evolution of a bigger brain is therefore a story of carbohydrate foods as much as animal foods: from sweet sugars to cooked starch, from chewing to processing, and from wadging to advanced nutrient extraction.