Meat wasn't on the menu for our ancient hominin ancestors

It’s widely believed that eating animal products gave early human relatives a boost in developing larger brains and stronger bodies. Many have argued that meat-based diets launched a chain reaction in our evolution, and that protein intake was linked to bigger brains and higher intelligence.

But new research is presenting a different picture of some ancient relatives: they might not have been munching on meat as often as we assumed.

Tooth enamel reveals a plant diet

Researchers analyzed tooth enamel in seven Australopithecus specimens uncovered in Sterkfontein, South Africa, and found that these early hominins consumed mostly plant-based foods. 

The work used a method for measuring stable nitrogen isotopes in fossilized enamel. Specialists in human origins have looked to nitrogen isotopes for diet clues in more recent remains, but the technology has now been applied to samples that are millions of years old.

“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,” explained Dr. Tina Lüdecke, a geochemist at the University of the Witwatersrand.

Meat-free diet challenges big brain hypothesis

Many hypotheses link meat consumption to expanded brain size in our lineage. Some researchers note that dense protein sources could have contributed to physiological changes, allowing for more complex cognition. 

The findings from Sterkfontein, however, indicate that these particular Australopithecus individuals didn’t eat a lot of meat.

Their nitrogen isotope ratios aligned with those of herbivores from the same timeframe, hinting at a diet that was plant-based rather than meat-centric.

Nitrogen isotope method

Scientists previously faced a big hurdle: organic matter degrades in bones older than about 200,000 years.

This new approach recovers nitrogen signals locked within tooth enamel, and can give us answers about diet dating much further back in time.

Researchers examined the enamel from these hominins and other animals. Herbivores showed distinct nitrogen isotope signatures compared to carnivores.

The isotope ratios in Australopithecus enamel specimens looked much more like the ratios found in the herbivore group, suggesting that the hominins had a limited meat intake.

Early humans did not have a meat-based diet

Legumes, seeds, and insects could still have been on the menu. Some experts think termites might have been an occasional source of protein. But the scientists noted that nothing in the results indicates frequent or heavy hunting of mammals. 

The findings fit with other archaeological evidence that hasn’t yet confirmed systematic meat consumption among early hominins at this period in time.

“Our method opens up exciting possibilities for understanding human evolution,” said Dr. Martínez-García, a researcher at the Max Planck Institute for Chemistry, who emphasized the significance of this approach. 

Greater context in hominin evolution

Australopithecus is a well-known genus of early hominins that walked upright and lived in parts of Africa between roughly 4 and 2 million years ago.

Lucy, discovered in 1974, is the most famous example of these ancient relatives. They had smaller brains than modern humans but were already showing certain traits that set them apart from other primates, such as upright posture. 

Speculations about their eating habits have varied, with some thinking they might have combined plant foods with regular meat. This new evidence challenges that notion for at least one population of Australopithecus.

Why it matters

Trying to unravel hominin diets helps anthropologists figure out what shaped our bodies and minds. Did meat-eating diets truly set the stage for rapid growth in brain volume and sophisticated tools?

Or were these changes linked to other factors like social cooperation, broader food choices, or climatic shifts?

Understanding that australopithecines didn’t rely heavily on meat raises fresh questions about what triggered key developments in our lineage.

Fossils reveal plant-based diet, not meat

Sterkfontein has been a hotbed of discoveries for nearly a century.

Excavations at this UNESCO World Heritage Site have produced many fossil finds, including some of the earliest evidence of bipedal hominins. Even after so many decades, the site continues to surprise.

“The research provides clear evidence that its diet did not contain significant amounts of meat,” said Professor Dominic Stratford, Director of Research at the Sterkfontein Caves. 

Studies of early hominin diets will keep evolving as technology improves. Analyzing tooth enamel for nitrogen might open a doorway to insights about other ancient species, and shed light on their place in the food chain.

That, in turn, informs the story of our family tree.

The study is published in the journal Science.

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