Counter to today’s depictions of cave-dwellers feasting on raw meat, early relatives of present-day humans ate little or no meat, according to new research.
Scientists at the Max Planck Institute for Chemistry in Germany and the University of the Witwatersrand in South Africa analysed tooth enamel samples from seven prehistoric humans of the genus Australopithecus who lived in southern Africa about 3.5 million years ago.
Published in the journal Science, the study looks at the remains from the Sterkfontein caves, a renowned 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 preserves an isotopic fingerprint of an animal’s diet,” says geochemist Tina Lüdecke.
Isotopes are different atomic masses of the same element that can occur simultaneously. “The nitrogen isotope ratio in the organic part of the enamel can last 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 for well-preserved fossils that are usually no older than a few tens of thousands of years.
This is because organic material, and thus nitrogen, disappears during fossilisation. Research teams at 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.
Plant-based predecessors
The heavy nitrogen 15N accumulates in the course of 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 that researchers can use the nitrogen isotope ratio in tissue samples to draw conclusions about where a creature fits into the food chain.
In this case, the research team compared samples from 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 like the sabre-toothed cat.
It found that the nitrogen isotope ratios in the enamel of seven Australopithecus teeth examined were consistently low. The values were therefore similar 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 the prehistoric human occasionally consumed protein sources such as eggs or termites.
It can be assumed that Australopithecus did not hunt large mammals, as the 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 assume that meat consumption heralded 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 future and answer the question of when meat actually appeared on the menu of prehistoric humans. “Our new methodology has the potential to answer other key questions about human evolution,” says Alfredo Martínez-García from the Climate Geochemistry Department at the Max Planck Institute.
The Sterkfontein Caves are a well-known fossil site near Johannesburg in South Africa. Many remains of so-called hominins have already been found there, including remains of the pre-human Australopithecus. Dominic Stratford/University of the Witwatersrand/dpa
