Ancient tooth enamel shatters long-held beliefs about early human diet

JOHANNESBURG — Breaking new ground in our understanding of early human diet and evolution, scientists have discovered that our ancient relatives may not have been the avid meat-eaters previously believed. Research reveals that Australopithecus, one of humanity’s earliest ancestors who lived in South Africa between 3.7 and 3.3 million years ago, primarily maintained a plant-based diet rather than regularly consuming meat.

Scientists have long debated when our ancestors began regularly consuming meat, as this dietary shift has been linked to several crucial evolutionary developments, including increased brain size and reduced gut size. Many researchers believed meat-eating began with early human ancestors like Australopithecus, partly because stone tools and cut marks on animal bones have been found dating back to this period.

“Tooth enamel is the hardest tissue of the mammalian body and can preserve the isotopic fingerprint of an animal’s diet for millions of years,” says geochemist Tina Lüdecke, the study’s lead author, in a statement. As head of the Emmy-Noether Junior Research Group for Hominin Meat Consumption at the Max Planck Institute for Chemistry and Honorary Research Fellow at the University of the Witwatersrand, Lüdecke regularly travels to Africa to collect fossilized teeth samples for analysis.

When living things digest food and process nutrients, they create a kind of chemical signature involving different forms of nitrogen. Think of it like leaving footprints in sand. Herbivores leave one type of print, while meat-eaters leave another. By examining these ancient chemical footprints preserved in tooth enamel, scientists can determine what kinds of foods an animal ate. Meat-eaters consistently show higher levels of a specific form of nitrogen compared to plant-eaters.

The research, published in Science, focused on specimens from the Sterkfontein cave near Johannesburg, part of South Africa’s “Cradle of Humankind,” an area renowned for its abundant early hominin fossils. Using innovative chemical analysis techniques, researchers examined fossilized teeth from seven Australopithecus specimens, comparing them with teeth from other animals that lived alongside them, including ancient relatives of antelopes, cats, dogs, and hyenas.

The findings challenge long-held assumptions about early human diet. The Australopithecus specimens showed nitrogen levels similar to plant-eaters and significantly lower than meat-eaters from the same period. However, they demonstrated remarkable dietary flexibility. The seven specimens showed more variation in their chemical signatures than any other species studied, suggesting they could adapt their diet based on what foods were available.

“This method opens up exciting possibilities for understanding human evolution, and it has the potential to answer crucial questions, for example, when did our ancestors begin to incorporate meat in their diet? And was the onset of meat consumption linked to an increase in brain volume?” says Alfredo Martínez-García from the Max Planck Institute for Chemistry.

The study also revealed that these early humans mainly ate C3 plants — trees, shrubs, and herbs — rather than grasses. Although the occasional consumption of small animals or insects cannot be ruled out, the study does not provide direct evidence of this behavior. Instead, the findings indicate that Australopithecus primarily relied on plant-based foods, potentially including energy-rich sources such as tubers, corms, or legumes.

Looking ahead, the research team plans to expand their investigation by collecting data from different early human species and time periods across eastern and southern Africa, as well as southeast Asia. This broader perspective could help pinpoint when regular meat consumption began and whether it provided evolutionary advantages.

“This work represents a huge step in extending our ability to better understand diets and trophic level of all animals back into the scale of millions of years,” notes Professor Dominic Stratford, Director of Research at the Sterkfontein Caves and study co-author.

This research not only changes our understanding of early human diet but also raises fascinating questions about human evolution. If Australopithecus thrived on a primarily plant-based diet, researchers must now investigate what other factors – beyond meat consumption – contributed to the development of larger brains and other distinctly human characteristics.