Natural sugars from fruit and honey may have supplied the energy that fuelled the expansion of the human brain, according to research published in Science by the University of Sydney and the University of Glasgow. The team built a model covering roughly four million years of human evolution, estimating the obligatory glucose demand of the brain, red blood cells, kidneys and reproductive tissues, and comparing it with the foods plausibly available across six evolutionary stages.
The analysis draws together food composition data, physiology, fossil isotope studies, dental morphology, archaeology, primate diets and genetics. It suggests early hominins relied heavily on carbohydrate-rich foods, particularly fruit, during the period when brain size grew from about 300 grams to roughly 1,500 grams in modern humans. Children's developing brains may consume as much as two-thirds of basal metabolic rate, and reproductive females likely needed substantially more glucose than other adults.
The model indicates that the mastery of fire and cooking later brought digestible starches from underground plants such as wild yams, water lily rhizomes and African potato into the diet, while grains arrived much later still. Co-author Professor Karen Hardy, Professor of Prehistoric Archaeology in Glasgow's School of Humanities, contributes through the UKRI-supported Powerful Plants project. The findings may also help explain the persistent human preference, strongest in children, for sweet foods.