Nitrogen isotopes in Australopithecus tooth enamel show no evidence of meat consumption
Pre-humans such as Australopithecus, who lived in southern Africa around 3.5 million years ago, ate little or no meat - this has been proven by Tina Lüdecke and her team at the Max Planck Institute for Chemistry using isotope measurements on fossil teeth. Together with researchers from Witwatersrand University in South Africa, the Mainz-based scientists analyzed tooth enamel samples from seven pre-humans. The ratio of heavy to light nitrogen isotopes showed that meat was rarely, if ever, on the menu of the australopithecines.
When our early ancestors started eating meat, it marked a decisive turning point in human evolution. This protein-rich diet is associated with, among other things, an increase in brain size and the ability to develop tools. Direct evidence as to when meat appeared in the diet of pre- and early humans and how its consumption developed has been lacking until now. However, researchers from the Max Planck Institute for Chemistry and Witwatersrand University in South Africa have now shown that pre-humans of the Australopithecus genus, who lived in southern Africa around 3.7 to 3.3 million years ago, ate mainly plants.
The team analyzed tooth enamel samples from seven pre-humans from Sterkfontein Cave, an important fossil site near Johannesburg. This region in South Africa is considered the cradle of humanity, as the remains of a very large number of hominins have been found there. The hominin family includes modern humans as well as their direct ancestors and close relatives. The researchers compared the results with tooth samples from animals living at the same time and in the same place, including apes, antelopes and carnivores such as hyenas, jackals and big cats such as the sabre-toothed cat.
Tooth enamel preserves an isotopic fingerprint of food
-Tooth enamel is the hardest substance in the body. It often preserves an isotopic fingerprint of an animal’s diet. The nitrogen isotope ratio in the organic part of the enamel can last for millions of years," says geochemist Tina Lüdecke, explaining the basis of a new detection method. Lüdecke has headed an Emmy Noether junior research group at the Max Planck Institute for Chemistry in Mainz since 2021 and is a visiting scientist at Witwatersrand University in Johannesburg. She regularly travels to Africa to take samples of fossil teeth.
When food is digested, degradation products are produced in the body. The excretion of these nitrogen compounds, for example in urine, feces or sweat, increases the ratio of -heavy- nitrogen (15N) to -light- nitrogen (14N) in the body compared to its food. Thus, herbivores have a higher nitrogen isotope ratio than the plants they consume and carnivores have a higher ratio than their prey. Therefore, the higher the ratio of the isotopes 15N to 14N of nitrogen in organic material, the higher the position of the organism in the food chain.
It has been possible for decades to reconstruct the diet of animals using nitrogen isotopes in hair, claws, bones or other organic material. However, nitrogen isotope ratios in collagen can only be measured in well-preserved fossils, which are generally not older than a few tens of thousands of years. This is because fossilization causes organic material to disappear and with it the nitrogen. However, the Mainz teams led by Tina Lüdecke and her colleague Alfredo Martínez-García have developed a method with which they can determine the nitrogen isotope ratio even in tooth enamel that is millions of years old.
Mainly vegetarian diet
The research team found that the nitrogen isotope ratios in the enamel of the seven Australopithecus teeth examined were variable, but remained consistently low - similar to those of herbivores and significantly lower than those of carnivores. From this, the scientists conclude that the diet of these pre-humans was varied, but largely - or even exclusively - plant-based. Australopithecus did not hunt large mammals, as Neanderthals did regularly a few million years later. Although the researchers cannot completely rule out the occasional consumption of animal protein sources such as eggs or termites, the evidence points to a predominantly vegetarian diet.
Further research on fossil tooth enamel
The highly sensitive determination of nitrogen isotopes in minute quantities of organic material can currently only be carried out at the Max Planck Institute for Chemistry in Mainz and at Princeton University in the USA. -Alfredo Martínez-García is confident that "our new method has the potential to answer further key questions about human evolution".
In the future, Lüdecke’s team plans to further develop the analysis method and expand their data sets. Specifically, she wants to take samples from younger and older human species from the cradle of humanity as well as from important hominin sites in eastern Africa or Southeast Asia. The aim is to find out when meat became part of the diet of our pre-humans, how this consumption developed and whether there was actually an evolutionary advantage as a result.
Tina Lüdecke’s research is supported by the Emmy Noether Program of the German Research Foundation (DFG).
Tina Lüdecke, Jennifer N. Leichliter, Dominic Stratford, Daniel M. Sigman, Hubert Vonhof, Gerald H. Haug, Marion K. Bamford, Alfredo Martínez-García
