Hunting animals and eating meat are considered important drivers of human evolution and a possible cause of our large brains. But it is still unclear when our ancestors added regular meat consumption to their diet. Now the tooth enamel of seven representatives of the pre-human Australopithecus from South Africa, who lived around three million years ago, provides new clues. The nitrogen isotopes preserved in the tooth enamel reveal that these pre-humans were vegetarians – similar to the great apes today. Meat, on the other hand, was not or only very rarely on their menu.
Most monkeys and great apes eat a predominantly plant-based diet. Baboons and chimpanzees, for example, occasionally hunt animals, but their meat is more of a rare feast than a regular part of their diet. This is different for us humans: our ancestors lived as hunters and gatherers, as some primitive peoples still practice today. This transition to meat consumption is considered a crucial turning point in human evolution. Because meat provides more calories, protein, and nutrients than plant-based foods, this dietary change may explain why prehumans began to develop increasingly larger brains relative to their primate relatives. Because of the higher energy density of meat, our ancestors also had to spend less time gathering and eating food – giving them more time to develop tools and learn from each other.
When did our ancestors start eating meat?
But it is still unclear which of our ancestors were the first to start eating meat regularly. “Stone tools and evidence of animal slaughter, such as cut marks on bones, provide evidence of regular consumption of meat and bone marrow around two million years ago,” report Tina Lüdecke from the Max Planck Institute for Chemistry in Mainz and her colleagues. This suggests that the early humans of the genus Homo were already hunters and gatherers. However, direct evidence for this is lacking. The data was even thinner for pre-humans such as the australopithecines, which lived in southern and eastern Africa more than three million years ago. There are also finds of stone tools from some of these hominins. “But whether the australopithecines specifically made these tools to hunt and disassemble animals is controversial,” explain the researchers.
One of the reasons for this is that the analysis of nitrogen isotopes, the most important method for determining the diet of fossil creatures, has not yet worked on such ancient relics. The ratio of the heavier nitrogen isotope 15N to the lighter variant 14N reveals whether an animal is a herbivore or a carnivore and how high up the food chain it is. The higher the proportion of nitrogen-15 in an animal’s tissues, the higher it is in the food chain.
However, the organic material in bones, hair, claws or tooth roots necessary for these isotope analyzes is generally only preserved well enough for a few tens of thousands of years. Therefore, this method has not yet been able to be used on hominin fossils that are millions of years old. However, Lüdecke and her team have developed a method with which they can determine the nitrogen isotope ratio in such relics. What is new is that the researchers do not examine bones or other easily degradable materials, but rather tooth enamel. It consists primarily of mineral, inorganic compounds and is therefore very durable. “But a small amount of organic material is trapped between and within these densely packed crystallites and is therefore protected,” explains the team. Thanks to particularly high-resolution, sensitive analysis techniques that have so far only been available twice in the world – at the MPI in Mainz and at Princeton University in the USA – Lüdecke and her team were now able for the first time to isotopically determine the diet of pre-humans, who lived 3.7 to 3.7 years ago lived 3.3 million years ago.
Australopithecus’ diet was similar to that of great apes
For their study, Lüdecke and her colleagues analyzed tooth enamel samples from seven representatives of the Australopithecus from the Sterkfontein Cave near Johannesburg. This fossil site in South Africa is considered one of the “cradles of humanity”. The team determined the nitrogen isotope values for pre-humans and compared them with samples from herbivores such as antelopes and monkeys, but also carnivores such as hyenas, jackals and big cats. The evaluations showed relatively close agreement between the nitrogen values from the australopithecine teeth and those from the herbivore samples, but significant differences from the values from the carnivores. “There is almost no overlap between the two. “The data therefore suggests a diet without substantial amounts of meat for these early hominins,” write Lüdecke and her team. The Australopithecus was therefore primarily vegetarian, even if the occasional consumption of animal protein sources such as eggs or termites cannot be completely ruled out.
The new results suggest that the australopithecines hardly differed from their ape ancestors and contemporaries in terms of their diet. They also fed primarily on fruits, nuts, leaves and other plant products. However, the prehumans from Sterkfontein Cave showed a greater individual range of isotope values than monkeys, antelopes and other pure herbivores. According to the researchers, this could indicate that some of these pre-humans also consumed meat in rare cases – similar to what chimpanzees still do today. “Given that our closest primate relatives use animal resources in this way, it would be logical to assume that our early ancestors also behaved in a similar way,” state Lüdecke and her colleagues. In the future, they plan to further develop their analysis method and also examine samples from younger and older human species from Africa or Southeast Asia. The goal: to find out when meat came into the diet of our pre-humans, how this consumption developed and whether there was actually an evolutionary advantage as a result.
Source: Tina Lüdecke (Max Planck Institute for Chemistry, Mainz) et al., Science, doi: 10.1126/science.adq7315