Contrary to current depictions of cave dwellers feasting on raw meat, early relatives of modern-day humans ate little or no meat, new research shows.
Scientists from the Max Planck Institute for Chemistry in Germany and the University of the Witwatersrand in South Africa analyzed tooth enamel samples from seven prehistoric humans of the genus Australopithecus who lived in southern Africa about 3.5 million years ago.
The research, published in the journal Science, looks at the remains of the Sterkfontein Caves, a well-known fossil site near Johannesburg in South Africa.
Many remains of so-called hominini have already been found there. These include modern humans, their direct ancestors, and other close relatives.
Tooth enamel reveals the diet
“Tooth enamel is the hardest substance in the body. It often contains an isotopic fingerprint of an animal’s diet,” says geochemist Tina Lüdecke.
Isotopes are different atomic masses of the same element that can occur at the same time. “The nitrogen isotope ratio in the organic part of the glaze can persist for millions of years.”
For decades it has been possible to determine the diet of animals based on nitrogen isotopes in hair, claws, bones or other organic material. However, this method only works with well-preserved fossils that are usually not older than several tens of thousands of years.
This is because organic material, and therefore nitrogen, disappears during fossilization. Research teams from the Max Planck Institute for Chemistry have now developed a method that can determine the nitrogen isotope ratio, even in tooth enamel that is millions of years old.
Vegetable predecessors
The heavy nitrogen 15N accumulates along the food chain from plants to carnivorous animals, compared to the light nitrogen 14N. Therefore, carnivores have a higher ratio of heavy to light nitrogen in the body than herbivores.
This means researchers can use the nitrogen isotope ratio in tissue samples to draw conclusions about where a creature fits in the food chain.
In this case, the research team compared samples of Australopithecus with teeth from animals that lived in the same place at the same time, including monkeys, antelopes and carnivores such as hyenas, jackals and big cats such as the saber-toothed cat.
It was found that the nitrogen isotope ratios in the enamel of seven Australopithecus teeth examined were consistently low. The values were therefore comparable to those of herbivores and significantly lower than those of carnivores.
The study therefore suggests a largely or even exclusively plant-based diet, although the researchers cannot completely rule out the possibility that prehistoric humans occasionally consumed protein sources such as eggs or termites.
It can be assumed that Australopithecus did not hunt large mammals, as Neanderthals, among others, regularly did several million years later.
Meat marked an evolutionary turning point
It is unclear when exactly meat appeared on the menu of our human ancestors. Nevertheless, researchers believe that meat consumption marked a decisive turning point in human evolution. Meat, as a protein-rich food, is associated with the increase in brain volume and the development of tools in human evolution.
The newly developed test method could lead to new insights in the future and provide an answer to the question of when meat actually appeared on the menu of prehistoric man. “Our new methodology has the potential to answer other important questions about human evolution,” says Alfredo Martínez-García of the Max Planck Institute’s Department of Climate Geochemistry.
The Sterkfontein Caves are a well-known fossil site near Johannesburg in South Africa. Many remains of so-called hominids have already been found there, including remains of pre-human Australopithecus. Dominic Stratford/University of the Witwatersrand/dpa