3 million years ago, our ancestors were vegetarian: Here’s the evidence, why it matters

New research suggests that our ancestors, such as Australopithecus, consumed little to no meat, relying instead on a primarily plant-based diet.

This discovery, published in the journal Science, challenges previous assumptions about the early dietary habits of “hominins”,  early members of the human lineage who lived approximately 3.5 million years ago, whose fossilised remains were found in southern Africa. 

The evidence: tooth enamel 

The study analysed nitrogen isotopes in the fossilised tooth enamel of seven Australopithecus individuals found in the Sterkfontein caves, about 45km south-east of Johannesburg. 

Tooth enamel, the hardest tissue of the mammalian body, can preserve the isotopic "fingerprint" of an animal's diet for millions of years.

Researchers from the Max Planck Institute for Chemistry in Germany and the University of the Witwatersrand used advanced techniques to detect isotopic signatures that reveal dietary preferences.

Nitrogen isotopes provide dietary insights of our early predecessors and tooth enamel, the hardest tissue in the body, preserves dietary information for millions of years.

“Nitrogen in tooth enamel is preserved for millions of years,” geochemist Tina Lüdecke, the study’s lead author, wrote in the journal Science. 

“We report enamel-bound organic nitrogen and carbonate carbon isotope measurements of Sterkfontein Member 4 mammalian fauna, including seven Australopithecus specimens. Our results suggest a variable but plant-based diet (largely C3) for these hominins. Therefore, we argue that Australopithecus at Sterkfontein did not engage in regular mammalian meat consumption.”

Plant-based diet

The research found that the nitrogen isotope ratios in Australopithecus enamel were “consistently low”, similar to herbivores, and much lower than contemporary carnivores. 

These findings indicate a diet composed largely or exclusively of plant-based foods, the scientists said.

While occasional consumption of animal protein, such as eggs or insects, cannot be ruled out, the data strongly suggest that Australopithecus did not regularly hunt or consume large mammals, as later species like Neanderthals did.

Why it matters: The evolutionary role of diet

The consumption of animal protein is widely regarded as a pivotal moment in human evolution, often linked to increases in brain size and the development of tools. 

However, the Witwatersrand research on Sterkfontein site suggests that meat consumption may have emerged much later in the evolutionary timeline.

This method opens up exciting possibilities for understanding human evolution, Alfredo Martínez-García of the Max Planck Institute, told Science Daily. He developed the isotope analysis technique used in the study,

Expanding the research

The team plans to apply this groundbreaking technique to fossils from other key sites in eastern and southern Africa, as well as Southeast Asia, to explore how and when meat consumption emerged and its potential impact on human development.

“This study provides clear evidence that Australopithecus had a predominantly plant-based diet,” said Professor Dominic Stratford, research director at the Sterkfontein Caves. 

“The Sterkfontein site continues to contribute crucial insights into our evolutionary past.”

Future work

The research, supported by the Max Planck Society and the Emmy Noether program of the German Research Foundation (DFG), marks a significant leap in understanding the diets of ancient hominins, paving the way for future studies on the role of diet in human evolution.