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  • Researchers propose that natural sugars were a primary energy source for early hominins, challenging the view that meat alone drove brain expansion.
  • The study models dietary shifts over four million years, showing sugar importance declined as cooking techniques allowed for starch digestion.
  • Experts note the findings complement rather than replace existing theories about animal protein's role in human evolution.

A new analysis published in Science suggests that natural sugars played a pivotal role in fueling the expansion of early human brains, offering an alternative perspective to long-held beliefs that meat consumption was the sole driver. Researchers argue that before humans mastered cooking techniques to unlock energy from starchy plants, our ancestors likely relied on glucose-rich foods such as ripe fruit and honey to meet the high metabolic demands of growing neural tissue.

The human brain is an energetically expensive organ, consuming approximately 20 percent of the body’s resting energy despite comprising only two percent of total body weight. This demand intensifies during childhood, with the brain utilizing up to 66 percent of a five-year-old’s energy reserves. Because the brain runs primarily on glucose derived from carbohydrates, early hominins faced significant challenges in securing sufficient fuel as their brains increased in size over millions of years.

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Previous scientific consensus has largely focused on animal-based foods, including meat, bone marrow, and fat, to explain how early humans powered their increasingly large brains. However, these food sources contain minimal carbohydrates. Without the ability to cook starchy plants like potatoes or grains, which requires heat to break down complex structures for digestion, early hominins needed another reliable source of glucose to support cognitive development.

To investigate this dietary gap, a team led by human nutrition scientist Jennie Brand-Miller constructed a model tracking hominin diets over the last four million years. The simulation began with a chimpanzee-like diet and progressed through various species, including Australopithecus afarensis, Homo habilis, Homo erectus, and modern humans. At each evolutionary stage, the researchers estimated brain and body sizes alongside the proportions of plant and animal foods consumed.

The model indicates that the earliest hominins may have derived more than 65 percent of their energy from naturally occurring sugars found in fruits and other sweet sources. This reliance on sugar likely diminished as early humans developed cooking methods that allowed them to extract glucose from wild yams, tubers, and eventually grains. The shift represents a transition from foraging for immediate sugar sources to processing complex carbohydrates.

The findings do not negate the importance of animal products in human evolution but rather highlight a parallel nutritional strategy. Brand-Miller described the roles of meat and sugar as complementary narratives rather than competing ones. Other experts, such as paleoanthropologist Marina Lozano, agree that both animal fats and plant-derived glucose were essential components of the hominin diet during this period.

However, reconstructing ancient diets involves inherent uncertainties. Some researchers question whether the study places the emergence of cooking too early in the timeline. Biological anthropologist Shara Bailey has previously argued that large brains were already established before there is clear evidence for widespread cooking practices. This debate underscores the difficulty in pinpointing exactly when and how dietary changes influenced biological evolution.

Understanding these ancient dietary patterns may also shed light on modern human preferences. The persistent craving for sweet foods could be an evolutionary remnant of a time when sugar was a scarce but vital resource for survival and brain development. As Brand-Miller noted, the desire for sweetness is deeply ingrained in human biology, reflecting its historical importance in sustaining one of evolution’s most demanding physiological projects.

The study adds nuance to our understanding of human origins by integrating nutritional science with paleoanthropology. While the exact timing and extent of sugar consumption remain subjects of ongoing research, the model provides a plausible mechanism for how early humans met their energy needs before agricultural practices transformed the global food supply. Future archaeological findings may further clarify the balance between sweet and savory elements in our ancestral diets.

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  • Smithsonian Magazine↗Meat Wasn't the Only Food That Drove Early Humans to Evolve Bigger Brains. Sugar May Have Fueled the Organ's Enlargement, Too