Early humans ate a surprisingly diverse and shifting diet over millions of years, starting with fruits, leaves, and other tree-based foods and gradually expanding to include grasses, sedges, meat, fish, and cooked starches. There was no single “early human diet.” What our ancestors ate changed dramatically depending on the species, the time period, and the environment they lived in.
The Earliest Hominins Ate Like Chimpanzees
Before about 4 million years ago, the earliest known human ancestors had diets dominated by foods from trees and bushes: fruits, leaves, seeds, and nuts. Carbon isotope analysis of fossilized teeth can distinguish between foods from trees and shrubs (called C3 plants) and foods from tropical grasses and sedges (C4 plants). The oldest hominin species with dietary data, Ardipithecus ramidus (around 4.4 million years ago) and Australopithecus anamensis (around 4 million years ago), show isotope signatures nearly identical to those of modern savanna chimpanzees. Their world was one of woodland foraging.
Around 3.5 million years ago, something changed. Multiple hominin species began incorporating grasses, sedges, or animals that fed on those plants into their diets. Australopithecus afarensis, the species famously represented by “Lucy,” shows highly variable isotope values, meaning some individuals ate mostly tree foods while others consumed substantial amounts of grass-based resources. A contemporary species from Chad, Australopithecus bahrelghazali, went even further and derived most of its carbon from these C4 sources. Exactly what they were eating remains debated. It could have been grass seeds, underground tubers of sedges, or even termites and other small animals that fed on grasses.
Dietary Paths Split Among Later Species
By about 2.5 million years ago, the hominin family tree had branched into species with very different dietary strategies. Paranthropus boisei in eastern Africa became a specialist, with roughly 80% of its diet coming from C4 resources like grasses or sedges. Its massive jaws and flat molars were built for heavy chewing. Its southern African relative, Paranthropus robustus, ate a more mixed diet, and the two species show no overlap in their isotope values despite being closely related.
Meanwhile, Australopithecus africanus maintained a highly varied, flexible diet mixing tree foods and grass-based resources. And Australopithecus sediba, living around 2 million years ago, swung back toward a strongly tree-based diet. This patchwork of dietary strategies shows that there was no single evolutionary march toward one type of eating. Different species solved the problem of survival in different ways, sometimes even within the same time period and landscape.
Meat Became Central With Homo Erectus
The emergence of Homo erectus around 1.8 million years ago marked a turning point. This species had a larger body, a significantly bigger brain, and a gut that was smaller relative to body size than earlier hominins. All of these changes point to a higher-quality diet, one richer in calories and nutrients per bite. Among primates, relative brain size correlates positively with dietary quality, and humans sit at the extreme end of that relationship. The expensive tissue of a large brain needs dense fuel to run.
Bioenergetic models estimate that Homo erectus needed roughly 2,700 calories per day. Plant foods alone could supply a maximum of about 1,000 of those calories, and animal protein contributed up to around 950 calories, with fat filling the gap. This made Homo erectus a true omnivore with a significant dependence on animal foods. Archaeological sites from this period consistently show associations between Homo erectus and large animal remains, including elephants and other megafauna. Fat, not just protein, was likely the prized resource. The human body can only process a limited amount of protein before it becomes toxic (a ceiling of roughly 35% of total calories), so fat from large animals was essential for meeting energy needs.
Cooking Changed Everything
The earliest evidence of cooking comes from Gesher Benot Ya’aqov in Israel, dated to 780,000 years ago. Researchers found pharyngeal teeth (throat teeth) from large carp species spatially clustered around ancient hearths, identified by concentrations of burned flint. X-ray analysis showed the teeth had been exposed to temperatures below 500°C, consistent with low-heat cooking rather than wildfire. This is the oldest confirmed evidence of hominins cooking food.
Cooking was transformative. It breaks down tough plant fibers and proteins, making calories and nutrients far more accessible. Starches that would pass through the gut largely undigested become a reliable energy source once heated. This likely allowed hominins to exploit a much wider range of plant foods and to extract more energy from animal tissue, supporting the caloric demands of ever-larger brains.
Neanderthals Ate Far More Plants Than Expected
Neanderthals are often portrayed as pure meat-eaters, and nitrogen isotope analysis does place them at the top of the food chain. In every population studied, Neanderthal bone collagen shows nitrogen values 3 to 5 parts per thousand higher than contemporary herbivores, matching or exceeding the values of wolves and hyenas. Their primary protein source was large herbivores like horses, bison, and deer.
But dental calculus, the hardened plaque on their teeth, tells a more nuanced story. Researchers recovered 73 starch grains from just three Neanderthal teeth found at sites in Iraq and Belgium. These included grains from wild relatives of wheat, barley, and rye, as well as date palms, legumes, and other plants. Many of the grass seed starches showed damage patterns that are a distinctive marker of cooking. This was true for Neanderthals living in warm Mediterranean climates and cold northern European ones alike, suggesting that plant processing and cooking were standard parts of the Neanderthal dietary toolkit, not occasional experiments.
The environment around one of the Iraqi sites supported date palms, walnuts, chestnuts, oaks, wild relatives of chicory and lettuce, and culinary herbs. Neanderthals were clearly drawing on this diversity.
Early Modern Humans Added Seafood
One of the clearest dietary distinctions between Neanderthals and early Homo sapiens is the use of aquatic resources. Along the coast of South Africa, Middle Stone Age humans were systematically exploiting shellfish by at least 120,000 years ago. These weren’t occasional meals. Sites like Klasies River contain thick deposits of shell, and the shellfish specimens from this period are notably larger than those from later periods, suggesting the resource was abundant and not yet under heavy pressure.
In Europe, the nitrogen isotope evidence is striking. The oldest directly dated modern human on the continent, a specimen called Oase 1 from Romania (around 40,000 years ago), has a nitrogen value of 13.3 parts per thousand. That is nearly 11 parts per thousand above contemporary ibex and 8 above red deer, far beyond what eating land animals alone could produce. It even exceeds the values of wolves and hyenas from the same site. The most likely explanation is significant consumption of freshwater fish, which carry elevated nitrogen values through their own food chains. Several other early modern humans from Romania show similarly extreme values.
This shift toward aquatic foods gave early Homo sapiens access to omega-3 fatty acids and other nutrients that may have further supported brain development and overall health. It also represented a broader pattern: modern humans consistently exploited a wider range of food sources than Neanderthals did, pulling calories from marine, freshwater, and terrestrial ecosystems simultaneously.
Macronutrient Balance Across Hunter-Gatherers
Studies of recent hunter-gatherer societies, the closest modern analogy to prehistoric diets, reveal a consistent pattern across different climates and continents. Protein intake is elevated compared to modern Western diets, typically ranging from 19 to 35% of total calories. Carbohydrates are lower, between 22 and 40% of energy. Fat fills in the remainder. This contrasts sharply with typical modern diets where carbohydrates often exceed 50% of calories, largely from domesticated grains and processed sugars that didn’t exist for most of human history.
The high reliance on animal foods across most hunter-gatherer groups, combined with the relatively low carbohydrate content of wild plant foods compared to cultivated crops, produces this characteristic ratio. Groups living at higher latitudes relied more heavily on animal foods, while tropical groups ate more plants, but the overall protein-fat emphasis held remarkably steady worldwide. Wild fruits, tubers, and greens simply contain less sugar and starch per bite than the domesticated versions we eat today.