The shift to consuming animal resources, especially meat, has been a significant focus in human evolution, with its role linked to brain development and tool usage. However, pinpointing when meat became a dietary staple has remained uncertain. Researchers from the Max Planck Institute for Chemistry in Germany and the University of the Witwatersrand in South Africa (Wits University) have now provided compelling evidence that Australopithecus species in southern Africa subsisted largely on plant matter between 3.7 and 3.3 million years ago.
The team conducted a stable isotope analysis on tooth enamel samples from Australopithecus fossils unearthed in the Sterkfontein Caves near Johannesburg. This site, part of South Africa's "Cradle of Humankind," is renowned for its extensive collection of early hominin fossils. The isotopic composition of the Australopithecus enamel was compared with samples from contemporaneous animals, including monkeys, antelopes, and predators such as hyenas and large cats.
"Tooth enamel is the hardest tissue in the mammalian body and can preserve the isotopic fingerprint of an animal's diet for millions of years," explained geochemist Tina Ludecke, the study's lead author. Ludecke heads the "Emmy-Noether Junior Research Group for Hominin Meat Consumption" at the Max Planck Institute for Chemistry and is an Honorary Research Fellow at Wits University's Evolutionary Studies Institute. She has traveled extensively to Africa to collect fossilized teeth for this innovative research. Wits University owns the Sterkfontein Caves and oversees the Australopithecus fossils housed there.
Understanding nitrogen isotope ratios has been key to unraveling dietary habits. When animals digest food, their bodies process nitrogen isotopes differently, excreting lighter isotopes (14N) through urine, feces, or sweat. This process increases the ratio of heavier isotopes (15N) in their tissues. Herbivores exhibit higher nitrogen isotope ratios than the plants they consume, while carnivores show even higher ratios due to their position in the food web.
Traditionally, nitrogen isotope studies have been limited to organic materials only tens of thousands of years old due to degradation over time. However, Ludecke utilized a novel technique from Alfredo Martinez-Garcia's lab at the Max Planck Institute for Chemistry to analyze nitrogen isotope ratios in fossilized tooth enamel dating back millions of years.
The findings revealed that nitrogen isotope ratios in Australopithecus tooth enamel were consistently low, similar to those of herbivores and much lower than those of contemporary carnivores. This suggests a predominantly plant-based diet for these early hominins. While researchers cannot entirely dismiss the occasional consumption of animal protein, such as eggs or insects, the evidence indicates that meat was not a regular part of their diet.
Ludecke and her colleagues aim to extend their research by studying additional fossils from other key sites across Africa and Southeast Asia. Their goal is to better understand when meat consumption began, how it evolved, and its potential role in the development of larger brain sizes in human ancestors.
"This method opens up exciting possibilities for understanding human evolution," noted Alfredo Martinez-Garcia. "It has the potential to answer critical questions, such as when our ancestors began incorporating meat into their diets and whether this change was linked to increases in brain volume."
Professor Dominic Stratford, Director of Research at the Sterkfontein Caves and a co-author of the study, remarked, "This work represents a huge step in extending our understanding of diets and trophic levels across millions of years. The research clearly shows that Australopithecus did not consume significant amounts of mammalian meat. We are honored to see this pioneering method applied to fossils from Sterkfontein, a site that has been a cornerstone of scientific discovery since Robert Broom's first hominin fossil find here 89 years ago."
Research Report:Australopithecus at Sterkfontein primarily consumed plant-based food
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