Were our ancestors vegetarian? 🌿

3.5 million years ago, Australopithecus, our distant ancestors, primarily fed on plants. A recent study, published in Science, reveals that contrary to what was previously thought, their diet was far from regular meat consumption.


This discovery, based on the analysis of nitrogen isotopes in fossilized tooth enamel, opens new perspectives on the evolution of human diet. Researchers compared the isotopic data of Australopithecus with that of other contemporary animals, revealing a predominantly plant-based diet.

Tooth enamel, a window into the past

Tooth enamel, the most resistant tissue in the body, preserves chemical traces of the diet for millions of years. Scientists analyzed fossilized teeth from the Sterkfontein cave in South Africa, a site rich in hominid fossils.

The nitrogen isotopes measured in these samples indicate that Australopithecus were at a trophic level close to herbivores. This innovative method allows tracing dietary habits with unprecedented precision.

A varied vegetarian diet

The results show that Australopithecus primarily consumed plants, with little or no meat. Although occasional consumption of termites or eggs is not excluded, their diet was largely plant-based.

This discovery contrasts with the idea that meat consumption played a central role in the early evolution of hominids. Australopithecus, unlike Neanderthals, did not hunt large mammals.

Towards a revision of human dietary history

Researchers plan to extend their analyses to other sites in Africa and Asia. The goal is to determine when and how meat became an important part of the human diet.

This method could also shed light on the links between diet and cognitive evolution. Questions about the impact of meat on brain development remain open.

To go further: What is an isotope and how does it reveal diet?

Isotopes are different versions of the same chemical element, having the same number of protons but a different number of neutrons. For example, nitrogen has two stable isotopes: nitrogen-14 (14N) and nitrogen-15 (15N). These isotopes behave differently in biological processes.

During digestion, organisms favor the lighter isotope (14N), which alters the ratio between 14N and 15N in their tissues. Herbivores have a higher 15N/14N ratio than the plants they consume, while carnivores have an even higher 15N/14N ratio than their prey. Thus, this isotopic ratio allows determining an organism's position in the food chain.

In the case of Australopithecus, the isotopic ratios measured in their tooth enamel indicate a diet close to that of herbivores. This method allows reconstructing ancient diets with great precision, even after millions of years.

What is a trophic network and how does it work?

A trophic network represents all the feeding interactions between organisms in an ecosystem. It shows how energy and nutrients flow between producers (like plants), consumers (herbivores and carnivores), and decomposers.

Each level of the trophic network is called a "trophic level." Plants, at the first level, capture solar energy. Herbivores, at the second level, eat these plants, and carnivores, at higher levels, feed on other animals. The higher up the network, the higher the nitrogen isotopic ratio (15N/14N) becomes.

In the study of Australopithecus, researchers used this principle to situate these hominids in their ecosystem. Their low 15N/14N ratio places them near herbivores, indicating a mainly plant-based diet.

What is tooth enamel and why is it so important for scientific studies?

Tooth enamel is the hardest tissue in the human body and in mammals in general. Composed mainly of minerals, it covers the crown of teeth and protects them from wear and damage. Its resistance allows it to survive extreme conditions for millions of years.

This tissue preserves chemical traces of the diet and the environment in which an individual lived. Isotopes of nitrogen, carbon, and other elements are trapped in it, offering a unique "fingerprint" of the organism's diet and trophic level.

In the study of Australopithecus, tooth enamel revealed that these hominids had a mainly vegetarian diet. This discovery was possible thanks to the analysis of nitrogen isotopes, which remain stable in enamel even after millions of years.