Human ancestors like Australopithecus — which lived around 3.5 million years ago in southern Africa — ate very little to no meat, according to new research published in the scientific journal Science. This conclusion comes from an analysis of nitrogen isotope isotopes in the fossilized tooth enamel of seven Australopithecus individuals. The data revealed that these early hominins primarily relied on plant-based diets, with little to no evidence of meat consumption.
The consumption of animal resources, especially meat, is considered a crucial turning point in human evolution. This protein-rich food has been linked to the increase in brain volume and the ability to develop tools. However, direct evidence of when meat emerged among our early ancestors, and of how its consumption developed though time, has been elusive. A team of researchers from the Max Planck Institute for Chemistry in Germany and the University of the Witwatersrand in South Africa (Wits University) now provide evidence that human ancestors of the genus Australopithecus that lived in southern Africa between 3.7 and 3.3 million years ago subsisted mostly on plants.
The research team analyzed stable isotope data from tooth enamel of Australopithecus individuals found in the Sterkfontein cave near Johannesburg, part of South Africa’s “Cradle of Humankind,” an area known for its rich collection of early hominins fossils. They compared the isotopic data of Australopithecus with that from tooth samples of coexisting animals, including monkeys, antelopes, and large predators such as hyenas, jackals, and big cats.
Tooth enamel preserved dietary signatures
“Tooth enamel is the hardest tissue of the mammalian body and can preserve the isotopic fingerprint of an animal’s diet for millions of years,” says geochemist Tina Lüdecke, lead author of the study. Lüdecke has led the “Emmy-Noether Junior Research Group for Hominin Meat Consumption” at the Mainz-based Max Planck Institute for Chemistry since 2021 and is an Honorary Research Fellow at the Evolutionary Studies Institute of the University of the Witwatersrand in Johannesburg. She regularly travels to Africa to sample fossilized teeth for her analysis. Wits University owns the Sterkfontein Caves and is the custodian of the Australopithecus fossils.
When animals digest food, biochemical reactions favor the “light” isotope of nitrogen (14N). Consequently, the degradation products that are produced in their body contain high proportions of 14N. The excretion of these “light” nitrogen compounds in urine, feces, or sweat increases the ratio of “heavy” nitrogen (15N) to this “light” nitrogen the body in comparison to the food it eats. This means that herbivores have a higher nitrogen isotope ratio than the plants they consume, while carnivores in turn have a higher nitrogen isotope ratio than their prey. Therefore, the higher the 15N to 14N ratio in a tissue sample, the higher is the trophic position of the organism in the food web.
Nitrogen isotope ratios have long been used to study the diets of modern animals and humans in hair, claws, bones and many other organic materials. However, in fossil material, these measurements have previously been limited to samples that are only a few tens of thousands of years old due to the degradation of organic material over time. In this study, Tina Lüdecke used a novel technique developed in Alfredo Martínez-García’s laboratory at the Max Planck Institute for Chemistry, to measure nitrogen isotopes ratios in fossilized tooth enamel that is millions of years old.
Evidence of mostly plant-based food
The team of researchers found that the nitrogen isotope ratios in the tooth enamel of Australopithecus varied, but were consistently low, similar to those of herbivores, and much lower than those of contemporary carnivores. They conclude that the diet of these hominins was variable but consisted largely or exclusively of plant-based food. Therefore,Australopithecus did not regularly hunt large mammals like, for example, the Neanderthals did a few million years later. While the researchers cannot completely rule out the possibility of occasional consumption of animal protein sources like eggs or termites, the evidence indicates a diet that was predominantly vegetarian.
Further research on fossilized tooth enamel
Lüdecke’s team plans to expand their research, collecting more data from different hominin species and time periods. They aim to examine fossils from other key sites in eastern and southern Africa as well as southeast Asia to explore when meat consumption began, how it evolved, and whether it provided an evolutionary advantage for our ancestors.
“This method opens up exciting possibilities for understanding human evolution, and it has the potential to answer crucial questions, for example, when did our ancestors begin to incorporate meat in their diet? And was the onset of meat consumption linked to an increase in brain volume?” says Alfredo Martínez-García, from the Max Planck institute for Chemistry.
“This work represents a huge step in extending our ability to better understand diets and trophic level of all animals back into the scale of millions of years. The research provides clear evidence that its diet did not contain significant amounts of meat. We are honoured that the pioneering application of this new method was spearheaded at Sterkfontein, a site that continues to make fundamental contributions to science even 89 years after the first hominin fossils were discovered there by Robert Broom,” says Professor Dominic Stratford, Director of Research at the Sterkfontein Caves and co-author of the paper.
The study was funded by the Max Planck Society. Tina Lüdecke’s research group is supported by the Emmy Noether program of the German Research Foundation (DFG).