Researchers have studied fossilised tooth enamel, which has revealed that human ancestors ate very little to no meat.

The conclusion comes from an analysis of nitrogen isotopes in the fossilised 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 increased 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 through 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 have uncovered evidence that human ancestors of the genus Australopithecus that lived in southern Africa between 3.7m and 3.3m years ago subsisted mostly on plants.

The research team 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 preservation

Tina Lüdecke, geochemist and lead author of the study, said, "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.”

When animals digest food, biochemical reactions favour the "light" isotope of nitrogen (14N). Consequently, the degradation products produced in their body contain high proportions of 14N. The excretion of these "light" nitrogen compounds in urine, faeces, 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. 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 the trophic position of the organism in the food web.

In this study, Tina used a novel technique at the Max Planck Institute for Chemistry, to measure nitrogen isotope ratios in a fossilised tooth enamel.

A plant-based food diet

The team of researchers found that the nitrogen isotope ratios in the tooth enamel of Australopithecus varied. However, they were consistently low, similar to those of herbivores, and much lower than those of contemporary carnivores.

They concluded 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 the Neanderthals did millions of years later.

While the researchers cannot completely rule out the possibility of occasional animal protein sources like eggs or termites, the evidence indicated a predominantly vegetarian diet.

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