How Fruit and Sugar Evolved the Human Brain Millions of Years Ago

Human evolution was fueled by a sharp shift away from fruit toward a diverse omnivorous diet, yet modern humans have never required less sugar while simultaneously depending on it for vital organ function, according to a recent review published in the journal Science.

Evolutionary Shifts in Primate Sugar Consumption

Four million years ago, the common ancestor shared by humans and chimpanzees relied primarily on fruit. According to Jennie Brand-Miller, emeritus professor at the University of Sydney, early hominins possessed vision tuned to distinguish the colors of sugar-rich, ripe fruits. Over millions of years, the proportion of daily energy derived from sugar dropped by about three-quarters as our lineage adopted an omnivorous diet rich in animal protein and fat.

Despite this reduction in overall sugar intake, organs dependent on glucose continued to expand. Modern human brains consume roughly 20 percent of the body’s baseline energy while accounting for only two percent of body weight. Karen Hardy, an archaeologist at the University of Glasgow and co-author of the study, notes that combining sugar needs with brain growth provides a clearer picture of human dietary drives.

High Glucose Demands in Reproductive-Age Women

The metabolic model developed in the study highlights high glucose requirements for specific demographic groups, particularly women of reproductive age. According to the research, women require between 200 and 250 grams of glucose daily due to the primary metabolic demands of the placenta, the fetus, and lactating mammary glands. Men require an estimated 150 to 200 grams daily, while children need about 125 grams.

Brand-Miller points out that meeting these nutritional thresholds remains difficult on standard modern diets, which often rely on vitamin and mineral supplements rather than addressing underlying carbohydrate balances. The study warns that ancestral populations could tolerate lower carbohydrate intakes more easily than modern humans, putting pregnant and breastfeeding women today at particular risk of a negative carbohydrate balance.

Contrasting Dietary Shifts and Archaeological Debate

The transition from a frugivorous diet to one incorporating complex carbohydrates and animal products is documented through physical reductions in gut size, teeth, and jaws, alongside genetic adaptations like sweet taste receptors and salivary enzymes. However, researchers debate the timeline of specific milestones, such as the control of fire. Marina Lozano, a researcher at the Catalan Institute of Human Paleoecology and Social Evolution (IPHES-CERCA), notes that species like Homo antecessor and pre-Neanderthals developed large brains without the use of fire to cook starch-rich foods, pointing out that widespread fire control did not emerge until the Neanderthal period.

Furthermore, researchers caution against the health impacts of modern refined sugars. Hardy explains that today’s refined sweets and snacks differ significantly from natural fruit sources, often delivering high calories while remaining devoid of essential micronutrients.

Frequently Asked Questions

How much sugar did our primate ancestors consume?

According to the Science study, early hominin ancestors consumed an estimated 400 grams of carbohydrates a day, with more than 65 percent of their daily energy derived from fruits and sweet items.

Why do women of reproductive age have higher glucose demands?

Women of reproductive age require 200 to 250 grams of glucose daily to support the metabolic needs of the placenta, the fetus, and lactating mammary glands.

Did early humans use fire to cook starchy foods?

While researchers agree that cooking grains and tubers helped incorporate starches into the diet, experts like Marina Lozano note that widespread fire control did not emerge until later with Neanderthals, meaning some earlier large-brained species evolved without cooked starches.