Your Sweet Tooth Is 4 Million Years Old

For decades, the story of how the human brain tripled in size went like this: our ancestors started hunting, ate more meat, and the extra protein and fat bankrolled the expansion. Tidy, satisfying, very paleo-diet-friendly. A study published in Science says we left out half the bill.

The brain accounts for just 2 percent of an adult's body weight but burns through roughly a fifth of the body's resting energy. Its preferred fuel is glucose, not protein, not fat, glucose. Scientists have long focused on animal-based foods to explain how early hominins powered their increasingly gluttonous brains. The problem: those foods contain few carbohydrates.

Researchers now argue that sugary fruits and honey provided between 20 and 35 percent of energy intake throughout most of human evolution. Early hominins likely raided bee nests and sought out ripe fruit, and the sugars in those foods may have helped power one of evolution's most calorically expensive projects: the human brain.

The supporting evidence is biological as much as dietary. Modern human biology, including sweet taste receptors, smaller guts and specific genes tied to sugar metabolism, appears to carry the fingerprints of a long evolutionary relationship with carbohydrate-rich foods. The demands scaled with development: in 5-year-old children, the brain's share of resting energy climbs to around 66 percent. Pregnant and breastfeeding females required significantly more dietary carbohydrates than adult males, suggesting that sugar availability may have directly shaped reproductive success and survival.

The researchers frame this as a parallel story, not a replacement for meat-based explanations. Still, reconstructing ancient menus requires some speculation, and at least one outside researcher questions whether the authors place widespread cooking too early in the timeline.

The brain built itself on honey raids and stolen fruit. Our sugar cravings are not a moral failing; they are a receipt.

Read the full story at Smithsonian Magazine, August 13, 2026

Hot Take: For four million years, evolution has been telling children to eat sugar. Then adults invented nutrition advice.