Plants came first. Our earliest ancestors were primarily plant eaters, and the shift toward meat happened gradually over millions of years. The last common ancestor we shared with chimpanzees was likely an opportunistic omnivore whose diet centered on ripe fruit, leaves, seeds, and other plant foods, with occasional animal protein from insects and small mammals. From that starting point, the human lineage slowly incorporated more and more meat, but plants remained the dietary foundation for millions of years before animal foods took on a significant role.
What Our Earliest Ancestors Ate
The oldest members of the human family tree, the early australopiths living around 4 to 6 million years ago, had diets that look almost entirely plant-based in the chemical record. Stable isotope analysis of their tooth enamel shows they consumed nearly pure C3 foods, a category that includes tree fruits, leaves, and woodland plants. Their teeth and jaws reinforce this picture: they were built not for tearing meat but for processing tough, fibrous plant material.
As African landscapes opened up and forests gave way to grasslands, these early hominins adapted by turning to a different kind of plant food. Underground storage organs like roots, tubers, corms, and bulbs became increasingly important, especially during dry seasons when fruits and leaves were scarce. These buried foods are energy-dense and abundant in the open habitats where early hominins lived. Digging them up with simple tools like sticks was likely one of the first forms of food technology, and researchers have proposed that sharing these extracted plant foods may have been a social behavior that predated any significant reliance on meat.
By around 2 million years ago, the isotope signatures shift noticeably. Some australopiths were eating predominantly C4 vegetation, meaning tropical grasses, sedges, or possibly animals that fed on those plants. Southern African australopiths and early members of our own genus, Homo, were getting roughly 30% of their diet from C4 sources. Whether that C4 signal reflects the plants themselves or the grazing animals that ate them is one of the key questions in the field.
When Meat Entered the Picture
The oldest physical evidence of meat eating comes from Dikika, Ethiopia, where researchers found animal bones bearing unmistakable stone tool marks dated to approximately 3.4 million years ago. The marks include cut lines from carving flesh off bone and percussion damage from cracking bones open to reach marrow. Both bones came from large mammals, one roughly the size of a goat, the other at least the size of a cow. The only hominin species present in that region at that time was Australopithecus afarensis, the species that includes the famous fossil “Lucy.”
These findings pushed the earliest known evidence of meat consumption back by nearly a million years. Before the Dikika discovery, the oldest confirmed butchery marks came from Bouri, Ethiopia, dating to about 2.5 million years ago. The Dikika marks were initially controversial, with some researchers suggesting they could have been caused by animal trampling. But detailed microscopic and chemical analysis showed deep, V-shaped, parallel marks that no experimental trampling could replicate. The scientific consensus now holds that stone tools made these marks.
What’s important to understand is that this early meat eating was almost certainly opportunistic. Early hominins weren’t hunting large prey. They were more likely scavenging carcasses left by predators, focusing on cracking open long bones to extract marrow, which is calorie-rich and relatively safe to consume compared to raw flesh that may carry pathogens.
How Meat Reshaped the Human Body
Over time, increasing access to animal foods left a clear imprint on human anatomy. The human gut tells a striking story when compared to our closest relatives. Great apes devote more than 50% of their gastrointestinal tract volume to the colon, which is specialized for fermenting low-quality plant material. Humans, by contrast, devote less than 20% to the colon. Instead, roughly 70% of the human gut is small intestine, a proportion similar to carnivores. The ratio of intestinal length to body length in humans is about 5:1, close to a dog’s 6:1 and far from a cow’s 12:1.
This gut structure reflects a long evolutionary shift toward energy-dense, easily digested foods. A smaller gut requires less metabolic energy to maintain, which connects to one of the most influential ideas in human evolution: the Expensive Tissue Hypothesis. The brain is extraordinarily costly to run, and a high-quality diet rich in animal fat and protein may have allowed the gut to shrink, freeing up metabolic energy for a larger brain. Fat plays a direct role in building brain tissue. Brain lipids consist of cholesterol and long-chain fatty acids that are essential for nervous system development.
The “Meat Made Us Human” Debate
A popular narrative holds that Homo erectus, which appeared around 1.9 million years ago, represented a major leap in meat consumption. This species had a larger brain, a smaller gut, bigger body size, and limb proportions similar to modern humans. All of these traits have been linked to increased carnivory in what’s sometimes called the “meat made us human” hypothesis.
But a 2022 study published in the Proceedings of the National Academy of Sciences challenged this story. When researchers corrected for how thoroughly different time periods have been excavated, they found no sustained increase in evidence of meat eating between 2.6 and 1.2 million years ago. The apparent spike in butchery evidence after Homo erectus appeared was largely an artifact of better-preserved, more thoroughly studied sites from that period. The actual rate of detectable carnivory remained essentially flat across that entire span.
This doesn’t mean meat was unimportant. It means the increase in meat consumption may have been more gradual and less tied to any single species than previously thought. Early archaeological sites with evidence of butchery predate Homo erectus entirely, and the dietary transition was likely a slow accumulation of skills, tools, and ecological pressures rather than a sudden revolution.
Plants Never Left the Menu
Even as meat became more prominent, plant foods remained central to the human diet throughout evolution. The emphasis on meat in evolutionary narratives partly reflects a bias in the archaeological record: stone tools and cut-marked bones preserve well, while roots, tubers, and fruits leave almost no trace. Researchers studying modern hunter-gatherer societies consistently find that gathered plant foods provide a large share of daily calories, often the majority, with hunting contributing a variable supplement depending on environment and season.
The real answer to “plants or meat first” is that plants were the original and continuous foundation. Meat was layered on top over millions of years, starting with opportunistic scavenging at least 3.4 million years ago, gradually increasing with better tools and cooperative hunting, and eventually helping to fuel the brain expansion that defines our lineage. But at no point did meat fully replace plants. The human digestive system, while clearly adapted for higher-quality foods than a gorilla eats, still depends on a mixed diet. We evolved as omnivores from omnivorous ancestors, with the balance shifting over deep time.