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

Scientists examined four million years of hominin diets. They found that natural sugars may have supplied energy—in the form of glucose—to growing brains before cooking made starchy foods easier to digest

Eli Stark-Elster | AAAS Mass Media Fellow

August 13, 2026 4:27 p.m.

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Long before soft drinks and cookies, our ancestors may have had a serious sweet tooth. Rather than reaching for sodas, early hominins likely raided bee nests for honey and sought out ripe fruit. The sugars in these foods may have helped power one of evolution’s most calorically expensive projects: the human brain, researchers reported August 6 in the journal Science.  

The findings point to another major driver of early humans’ enlarged brains and could also help explain the origins of our sugar cravings today.

“I think we should recognize that sweetness is something really important to humans, and that desire should be satisfied on a regular basis,” study co-author Jennie Brand-Miller, a human nutrition scientist at the University of Sydney in Australia, tells Scientific American’s Jackie Flynn Mogensen.

The human brain is a glutton. Despite making up only about 2 percent of an adult’s body weight, the organ consumes roughly 20 percent of the body’s energy at rest. Demands are even greater during childhood: around age 5, the brain uses about 66 percent of the body’s energy.

The greedy bit of tissue runs on glucose, broken down from carbohydrates. They often come from starches, found in potatoes, corn and bread, as well as sugars in fruits and honey. Today, it isn’t hard to find enough food to meet the brain’s energy needs. But early hominins may have had a hard time satiating the organs as they grew throughout evolution.  

Scientists have often focused on animal-based food sources—meat, bone marrow and fat—to explain how early hominins managed to power their increasingly gluttonous brains. But those products contain few carbohydrates. What’s more, our ancestors couldn’t have gotten glucose from starchy foods before the advent of cooking, Brand-Miller says in a statement, so they must have gotten their glucose fix some other way.  

To investigate, Brand-Miller and colleagues examined how hominin diets and dietary needs evolved over the last four million years, during which brain size ballooned from 300 grams to 1,500 grams. They built a model beginning with a chimpanzee-like diet that moved through those of Australopithecus afarensis, Homo habilis, H. erectus and modern human, or H. sapiens, foragers. At each stage, the team estimated the brain and body sizes of the hominin species, the relative proportions of plant and animal foods they consumed and the glucose required by their brains and other tissues.

The earliest hominins, the researchers calculated, may have acquired more than 65 percent of their energy from naturally occurring sugars in fruits and other sweet foods. However, those items probably became less important once early humans began cooking starchy plants—wild yams and other tubers, followed later by grains—that could provide an alternative source of glucose.

The findings do not mean that animal products weren’t important to hominin evolution. Rather, they highlight sugar’s less-studied role. “I see them as parallel stories, not one replacing the other,” Brand-Miller tells Science News’ Jake Buehler.

Paleoanthropologist Marina Lozano, who was not involved with the research, agrees. The model supports the view that “animal protein and fats and plant-derived glucose have been key,” says Lozano, of the Catalan Institute of Human Paleoecology and Social Evolution in Spain, to El País’ Ana Lozano del Campo, per a translation by Smithsonian magazine.

Still, reconstructing the structure and timing of these ancient menus does require some speculation. Lozano questions whether the authors place widespread cooking too early.

Debates over the emergence of cooking predate the new paper. In 2015, for instance, some of the researchers involved in the Science study reported that cooked starch was crucial for brain growth in early humans. But at the time, biological anthropologist Shara Bailey of New York University told NPR’s Angus Chen that “large brains were already established by the time we have any good evidence for cooking.”

Eli Stark-Elster is the AAAS Mass Media Science & Engineering Fellow at Smithsonian magazine. He is a PhD student in evolutionary anthropology at the University of California, Davis. His research focuses on documenting the methods used to induce altered states of consciousness across cultures—he conducts fieldwork in southern Africa, where he studies the shamanic use of hallucinogenic plants and fungi. His writing and research has been featured on NPR, Psyche and the Conversation. He also writes on his Substack, Unpublishable Papers.