Australopithecus afarensis skull (© Iliya Mitskavets - stock.adobe.com)
In a nutshell
- Australopithecus relied primarily on plant-based diets, not meat, challenging the long-held belief that meat consumption drove human brain evolution.
- The wide variation in nitrogen isotope values suggests these early hominins had highly adaptable diets, potentially explaining their success across diverse African environments.
- Dietary flexibility, rather than meat consumption, may have been the key evolutionary advantage that set our ancestors on the path to becoming human.
MAINZ, Germany — For decades, scientists have believed that meat-eating drove human evolution, particularly our enlarged brains. This carnivorous origin story has become so entrenched that few questioned it: our ancestors supposedly began eating substantial amounts of meat, which provided rich nutrients that fueled brain growth and helped make us human. But new research turns this idea on its head.
Scientists analyzing tooth enamel from Australopithecus fossils at Sterkfontein, South Africa, found something unexpected: these early human relatives who lived around 3.7 to 3.3 million years ago weren’t eating much meat at all. The study, led by Tina Lüdecke from the Max Planck Institute for Chemistry, reshapes what we thought we knew about early human diets.
The team examined nitrogen isotopes preserved in tooth enamel, which act like dietary fingerprints. This method gave them a direct window into what Australopithecus actually ate, replacing educated guesses based on circumstantial evidence like stone tools or anatomical features.
Lüdecke describes this gap in our knowledge as “frustrating” for scientists. While we’ve known that by the time our genus Homo appeared over two million years ago, hominins were using stone tools to butcher animals, we’ve never been sure when regular meat-eating began or which species started it.
How Australopithecus’ Teeth May Solve An Evolutionary Mystery
Australopithecus walked upright, had human-like hands, and thrived across Africa for nearly two million years. Previous studies of their teeth and jaws suggested various diets—from fruits and leaves to underground tubers—but couldn’t determine if they regularly ate meat.
Until now, scientists could only measure nitrogen isotopes in collagen, the organic component of bone that breaks down within 300,000 years. This limitation made analyzing 3-million-year-old specimens impossible.
The breakthrough came by targeting tiny amounts of organic matter trapped within tooth enamel, which stays preserved much longer thanks to enamel’s dense structure.
Lüdecke started this journey during her PhD, first measuring carbon isotopes in tooth enamel to study plant diets. In an article she published on The Conversation, she recounts how the team built their method: “We started small by testing the method on rodent tooth enamel from animals with controlled diets in a specialized feeding experiment. It worked. From there, we moved on to the enamel of wild mammals from museum collections and other animals that had lived naturally in African ecosystems.”
Plant-Based Diet Prevails
The team analyzed 43 specimens from Sterkfontein, including seven Australopithecus teeth, and compared them with contemporaneous animals including antelopes, cats, dogs, and hyenas.
The results, published in Science, showed Australopithecus had nitrogen values matching herbivores, not carnivores. The difference was clear and significant—their nitrogen-15 levels were 5.6 parts per thousand lower than carnivores, firmly placing them in the plant-eating category.
What stood out was how variable their diets were—they showed a wider range of nitrogen values than any other species analyzed. This suggests they were adaptable eaters who changed their diets based on what was available or what season it was.
What Did An Australopithecus Dinner Look Like?
Carbon data from the same teeth showed Australopithecus ate mostly trees, bushes, and fruits (C3 plants), with some tropical grasses and sedges (C4 plants) mixed in. Together with the nitrogen data, this paints a picture of resourceful plant foragers with varied diets.
They likely dug for energy-rich tubers, corms, and bulbs that other animals couldn’t easily access. They might have occasionally eaten insects or termites, but they weren’t regularly hunting or scavenging mammals.
As Lüdecke explains on The Conversation: “Our findings suggest that these ape-like, small-brained early hominins were eating mostly plants. There was little to no evidence of meat consumption. They may have snacked on the occasional egg or insect but they were not regularly hunting large mammals like Neanderthals did millions of years later.”
Beyond the Meat-Brain Connection
If meat didn’t drive brain enlargement in early human species, what did? Maybe cooking plant foods played a role, making nutrients more accessible and easier to digest. Or perhaps energy-rich plant foods like starchy tubers were the key.
The study doesn’t rule out meat becoming important later in human evolution, just that it wasn’t driving our evolutionary path during the time of Australopithecus.
We know that more recent ancestors, including Neanderthals and early Homo sapiens, were regular meat-eaters based on their isotope studies. The shift to more meat likely happened somewhere between Australopithecus and these later species, possibly when more sophisticated tools emerged.
This aligns with what we see in modern non-human primates. Chimpanzees and bonobos, our closest living relatives, get about 95% of their calories from plants, occasionally eating small mammals or insects.
Adaptability: Our True Evolutionary Superpower
This study suggests human evolution wasn’t a simple story of becoming meat-eaters. Instead, our ancestors adapted their diets to whatever environments they found themselves in.
The dietary flexibility shown by Australopithecus may have been the real evolutionary advantage that helped our lineage thrive. Being able to eat a wide variety of foods—not specifically meat—allowed our ancestors to survive in changing environments.
This adaptability foreshadows how modern humans have been able to inhabit nearly every environment on Earth.
Lüdecke and her team are already looking ahead: “This discovery is just the beginning,” she writes. “We’re now expanding our research to other fossil sites across Africa and Asia, hoping to answer bigger questions. When did meat truly enter the hominin diet? Which species of hominins through our evolution consumed meat? Did the behavior emerge several times and did it coincide with the rise of larger brains, or marked changes in behavior, like new stone tool technology?”
With so many questions to answer, it’s only a matter of time before experts figure out when meat became a staple in the human diet.
Paper Summary
Methodology
Researchers analyzed nitrogen isotopes preserved in tooth enamel from seven Australopithecus specimens and 36 other mammals from the same fossil deposits at Sterkfontein Cave in South Africa, dated to approximately 3.7-3.3 million years ago. Tooth enamel preserves tiny amounts of original organic material, including nitrogen, which can reveal an animal’s position in the food chain. Animals higher in the food chain (carnivores) typically have higher levels of nitrogen-15 compared to nitrogen-14 than those lower in the food chain (herbivores).
The researchers used a high-sensitivity method to extract and analyze this nitrogen from the enamel, allowing them to determine the relative proportions of these isotopes. Atoms of the same element can have different versions, called isotopes, which have the same number of protons but different numbers of neutrons, making them slightly heavier or lighter but chemically similar. In food webs, nitrogen isotopes become enriched as you move up the chain, meaning predators have higher nitrogen-14/nitrogen-15 ratios than herbivores. The team also measured carbon isotopes in the same teeth, which indicate whether animals consumed mostly C3 plants (trees, bushes) or C4 plants (tropical grasses). By comparing the nitrogen and carbon values of Australopithecus with known herbivores and carnivores from the same ecosystem, the researchers could determine where these early hominins fit in the ancient food web.
Results
The nitrogen isotope values of Australopithecus specimens were statistically indistinguishable from those of herbivores but significantly different from carnivores. The median nitrogen-15 value for Australopithecus was 5.6‰ lower than that of carnivores, with essentially no overlap between the two groups. This strongly indicates a diet without substantial proportions of mammalian meat. Interestingly, the Australopithecus specimens showed the widest range of nitrogen isotope values (6.7‰) of any analyzed group, suggesting highly variable diets. Carbon isotope analysis revealed that Australopithecus consumed primarily C3 plants with some C4 input, indicating they ate mostly foods from trees and bushes with some tropical grasses or sedges. When plotted together, the nitrogen and carbon isotope data showed that Australopithecus occupied the same isotopic niche space as herbivores and other primates, not carnivores, confirming their primarily plant-based diet.
Limitations
The study examined only seven Australopithecus teeth, though this represents a good portion of available fossils. Two teeth were first molars, which form during infancy and might show nursing signals rather than adult diet. The research focused only on Sterkfontein specimens, so findings might not apply to all Australopithecus populations across Africa.
The method also can’t distinguish between plant-eating and insect-eating, and wouldn’t detect occasional meat consumption if it was infrequent.
Discussion & Takeaways
This research challenges the idea that meat-eating drove human evolution. Australopithecus at Sterkfontein ate mostly plants, not meat. Their varied nitrogen values show they had flexible diets, likely eating different foods than other animals in their environment.
This flexibility, not meat-eating, may have been what helped them thrive in diverse African environments. Regular meat consumption probably came later in human evolution, possibly with the genus Homo, and other factors like cooking might explain our increasing brain size.
Publication Information
The study “Australopithecus at Sterkfontein did not consume substantial mammalian meat” appeared in Science (Volume 387, pages 309-314) on January 17, 2025. Tina Lüdecke from the Max Planck Institute for Chemistry led the research team, with collaborators from Germany, South Africa, and the United States. Lüdecke also shared insights in The Conversation on March 3, 2025.
