Forget the image of primitive man hunting to obtain meat: our most distant ancestors, the Australopithecusthey were vegetarians. This was revealed by a study published in the prestigious journal Science, the result of a collaboration between the Max Planck Institute for Chemistry in Germany and theUniversity of the Witwatersrand in South Africa. The research, guided by geochemistry Tina Lüdeckefocused on the analysis of seven fossilized molars of Australopithecus africanus found in Sterkfontein Cavenear Johannesburg, a paleontological site known as “Cradle of humanity” for the wealth of hominid fossils.
These hominids, lived between 3.7 and 3.3 million years agothey walked upright and had long arms suitable for climbing trees and a smaller brain than modern man. The analysis of nitrogen isotopes in tooth enamel made it possible to reconstruct their dietrevealing a plant-based diet, with negligible meat consumption.
“The relationship between two different forms of nitrogen – explains Lüdecke – allows us to distinguish between herbivores and carnivores. In the case of theAustralopithecus africanus, the results show a clear affinity with herbivoreslike antelopes, rather than with carnivores.”
An unexpected result
This discovery calls into question the long-held hypothesis that meat consumption was a crucial factor in the increase in brain size during human evolution. “Meat – explains Lüdecke – is a concentrated source of calories and nutrients, essential for fueling a large brain, but our data suggest that theAustralopithecus africanus did not use it regularly“.
On this week’s #SciencePodcast researcher Tina Lüdecke describes how her team used nitrogen isotope ratios from the tooth enamel in seven Australopithecus individuals to determine what predominated in their diets at the time—meat or veg.
Listen here:… pic.twitter.com/mwWmYXncWZ
— Science Magazine (@ScienceMagazine) January 22, 2025
“If we had discovered that theAustralopithecus he consumed considerable quantities of meat – he adds Alfredo Martínez-Garcíaco-author of the study and director of the Organic Isotope Geochemistry Laboratory at the Max Planck Institute for Chemistry – we would have concluded that the subsequent expansion of cranial volume in other hominin species was not due to the onset of meat consumption.”
Nitrogen isotopes: a window into the past
But how was it possible to reconstruct the diet of these hominids who lived millions of years ago? The key lies in the analysis of nitrogen isotopes present in the enamel of fossilized teeth.
When animals feed, they assimilate the nitrogen present in the food. This element exists in two forms, or isotopes: “light” nitrogen (¹⁴N) and “heavy” nitrogen (¹⁵N). The ratio between these two isotopes varies depending on the organism’s position in the food chain. Herbivores, which feed on plants, have a lower ¹⁵N/¹⁴N ratio than carnivores, which feed on other animals.
By analyzing the ¹⁵N/¹⁴N ratio in the tooth enamel ofAustralopithecus africanusresearchers were able to determine that his diet was primarily plant-based, similar to that of contemporary herbivores.
New questions about human evolution
The research opens new scenarios and raises new questions. “If theAustralopithecuswith a smaller brain than later hominids, did not consume substantial quantities of meat, what factors contributed to the expansion of the brain in the human evolutionary line?”, asks Alfredo Martínez-García.
It is possible that other factors, such as the variety of plant-based diet, the intake of specific nutrients or the introduction of new food preparation methodshave played an important role in brain development.
“The critical questions remain: who first started eating meatwhen did it happen and when did it become a significant enough resource to drive morphological adaptations?”, says Lüdecke.
The investigation will continue with the analysis of other fossils, coming from different sites in eastern and southern Africa, to reconstruct the evolution of the diet in our ancestors and understand when and why meat became a fundamental food for our species.
This discovery aboutAustralopithecus africanus adds an important piece to the complex puzzle of human evolution. Far from being a definitive answer, it opens up new research perspectives and invites us to rethink the role of diet in our long evolutionary journey.
