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New research suggests that naturally occurring sugars may have played a crucial role in fueling the evolution of the human brain over millions of years. A study led by scientists from the University of Sydney and the University of Glasgow models the dietary requirements of early humans and their ancestors, showing that carbohydrates, particularly from fruits, honey, and underground plant foods, may have been essential in meeting the rising glucose demands of an expanding brain. Published in Science, the findings challenge conventional theories that emphasize meat consumption as the main driver of human evolution. The research team constructed a detailed model tracing human evolution over roughly four million years, analyzing whether dietary carbohydrates could supply the necessary glucose to support the growth of increasingly complex brains. According to the study, raw starches were largely inaccessible as a glucose source, forcing early humans to rely heavily on naturally sweet foods long before grains and tubers became common parts of the diet. This reliance on carbohydrates may explain the modern human preference for sweetness, according to lead researcher Jennie Brand-Miller, a professor of human nutrition at the University of Sydney’s Charles Perkins Center. Human brain size expanded dramatically over this time span, growing from about 300 grams in early hominins to nearly 1,500 grams in modern humans. Alongside this increase, the brain’s demand for glucose rose significantly. Glucose is the primary energy source for the brain, as well as for other critical tissues such as red blood cells, kidneys, and reproductive organs. For much of human history, this glucose would have primarily come from naturally occurring carbohydrates rather than from cooked starchy foods. To understand how early humans met these escalating glucose needs, the researchers created a model that examined six distinct evolutionary stages. Each stage considered the availability of both animal and plant-based foods, assessing how changes in diet might have influenced carbohydrate access. The model incorporated data from multiple disciplines, including food composition, metabolism, physiology, fossil isotope analysis, dental morphology, archaeology, primate diets, and genetics. The results suggest that early hominins, such as Australopithecus afarensis (commonly known as “Lucy”), Homo habilis, and Homo erectus, depended heavily on carbohydrate-rich foods, especially fruits. As fire and cooking techniques advanced, underground plant foods like wild yams, water lily rhizomes, and African potatoes began contributing more significantly to glucose intake. However, grains and other processed carbohydrates entered the human diet far later, with the first evidence of grain processing dating back to around 65,000 years ago. Brand-Miller emphasized that while animal foods were undeniably important in human evolution, the specific need for glucose to sustain the brain has been underappreciated by many anthropologists. She noted that the human brain’s unusual size relative to body mass necessitates a high-energy supply, which would have been difficult to achieve without sufficient carbohydrate intake. The study also highlighted the significance of glucose during pregnancy and lactation. Female reproductive systems require additional glucose to support fetal development, placental function, and milk production. These metabolic demands may have further reinforced the necessity of a carbohydrate-rich diet throughout human evolution. The research provides a fresh perspective on the nutritional foundations of human evolution, suggesting that the availability and consumption of naturally sweet foods were pivotal in enabling the expansion of the human brain. It challenges existing narratives that focus predominantly on protein and fat as the driving forces behind cognitive advancement. Instead, it underscores the potential role of carbohydrates in shaping one of humanity’s defining traits, the capacity for complex thought and behavior. Further studies will explore how these dietary patterns influenced social structures, tool use, and cultural developments among early humans. Researchers plan to investigate how shifts in food availability and preparation methods impacted brain development across different regions and time periods.