
A new study by Tina Lüdecke and colleagues provides a critical analysis of the dietary habits of Australopithecus at Sterkfontein Cave, challenging long-held assumptions about the role of meat consumption in hominin evolution. The research is based on a novel approach that utilizes nitrogen and carbon isotope analysis of tooth enamel, allowing for the study of much older samples than traditional methods. The study’s findings suggest that Australopithecus diets were largely plant-based, with no evidence of regular consumption of substantial amounts of mammalian meat. This conclusion is significant because it contradicts the hypothesis that meat consumption was a driving factor in the development of key hominin traits like increased brain size.

This conclusion is supported by comparing the nitrogen-15 to nitrogen-14 ratios in Australopithecus tooth enamel to that of herbivores and carnivores from the same time period. By combining nitrogen and carbon isotope analysis of tooth enamel, the researchers were able to reconstruct the diets of Australopithecus and other mammals from the Sterkfontein M4 deposits, providing new insights into the dietary ecology of early hominins. The method provides a more robust and quantitative approach to studying the diets of fossil hominins.
The Australopithecus specimens’ nitrogen isotope values are statistically similar to those of herbivores and significantly lower than those of carnivores, indicating that they did not regularly eat meat. These findings may challenge the idea that a transition to regular meat consumption drove evolutionary changes, such as increased brain size, in the hominin lineage.

While Australopithecus diets were largely plant-based, there was a high degree of variability in the diets of the seven Australopithecus specimens analyzed, greater than any other fossil or modern taxon. This variability may be due to individual preferences, seasonal availability of food, or the consumption of resources like legumes, geophyte corms, and insects, which have variable nitrogen-15 to nitrogen-14 ratios. The carbon isotope data indicates that the Australopithecus diet consisted primarily of C3 plants, with a minor and variable contribution of C4 plants. The carbon and nitrogen isotope values of Australopithecus overlap with those of non-hominin primates and browsing bovids, indicating they shared similar food resources. These findings suggest Australopithecus were adaptable and opportunistic feeders.
The study uses a novel method to analyze the diets of Australopithecus by measuring stable isotope ratios in tooth enamel. This approach overcomes the limitations of traditional methods that rely on collagen from bone or dentin, which degrades over time, making it difficult to analyze samples older than ~20,000 years. Tooth enamel, on the other hand, is more resistant to diagenetic alteration due to its high hydroxyapatite content, which protects the small amounts of organic matter trapped within its crystallites.
Methodology
Key aspects of the methodology include:
- Nitrogen isotope analysis: The ratio of nitrogen-15 to nitrogen-14 (expressed as δ15N) is used as a trophic indicator. Metabolic processes lead to a higher concentration of 15N in consumer tissues relative to their diet, with a trophic enrichment of approximately 3 to 6‰. The researchers measured δ15N in tooth enamel (δ15Nenamel) of fossil specimens to determine their trophic position.
- Carbon isotope analysis: The stable carbon isotopic composition (δ13C) of enamel carbonate reflects the contribution of C3 versus C4 plants to an animal’s diet. This analysis helps distinguish between animals that primarily consume plants from the majority of dicots (C3) versus mostly monocots (C4).
- Sample collection: The study analyzed 43 fossil specimens from Sterkfontein Member 4 (M4) deposits, including seven Australopithecus specimens, as well as other mammals such as Cercopithecidea, Bovidae, Felidae, Canidae, and Hyaenidae. Additionally, modern enamel samples from African fauna were used for comparison.
- Data analysis: The researchers compared δ15Nenamel values of Australopithecus with those of herbivores and carnivores from the same time period. They also analyzed δ13Cenamel values to understand the types of plants consumed. Statistical methods such as Stable Isotopes Bayesian Ellipses (SIBER) were used to determine dietary niche overlaps.
- Focus on enamel: The analysis of enamel-bound organic nitrogen allows for the study of older fossils, extending the record beyond the limitations of collagen-based methods. The method is highly sensitive and can be used to analyze the small amounts of organic matter preserved in tooth enamel.
- Consideration of weaning: The study included two first molars in the Australopithecus dataset which likely formed before weaning. Breast milk consumption can lead to elevated δ15N values in nursing offspring, which was considered when interpreting the results of the first molar samples.
- Controlling for environmental factors: The range of δ15Nenamel values for the Pliocene M4 fauna was found to be comparable to that of modern African fauna, which suggests similar nitrogen isotopic baselines, which supports the reliability of the measurements.
Strengths of the Study
- Novel Methodology: The study’s use of tooth enamel to measure stable isotope ratios is a significant advancement. Unlike collagen from bone or dentine, tooth enamel is more resistant to diagenetic alteration, allowing for the analysis of samples millions of years old. This opens new avenues for studying the dietary ecology of early hominins.
- Robust Data: The researchers analyzed a large dataset of 43 fossil specimens, including seven Australopithecus, as well as other mammalian families, and compared these with modern samples. This comparative approach strengthens the conclusions by establishing a baseline for interpreting the isotope data.
- Clear Trophic Distinction: The study clearly distinguishes between herbivores and carnivores based on their nitrogen isotope values, providing a strong basis for evaluating the trophic position of Australopithecus. The median δ15Nenamel of bovids is 6.0‰ lower than that of carnivores, which is consistent with a 3 to 6‰ difference between predator and prey.
- Dietary Variability: The research highlights the significant dietary variability among Australopithecus specimens, indicating they were adaptable and opportunistic feeders. This variability, which is greater than that of other fossil and modern taxa, suggests that Australopithecus exploited a wide range of food resources, including plants, insects and possibly legumes.
- Consideration of Weaning: The study acknowledges the potential impact of breastfeeding on the nitrogen isotope values of first molars, which form before weaning. The researchers address this by considering whether the higher δ15Nenamel values in some individuals could be attributed to nursing rather than meat consumption.
- Statistical Rigor: The study utilizes statistical methods, such as the Stable Isotopes Bayesian Ellipses (SIBER), to determine dietary niche overlaps. This enhances the reliability of the interpretations and provides an estimate of the isotopic niche width for the different taxonomic groups.
Potential Limitations and Points for Consideration
- Sample Size of Australopithecus: While the study included seven Australopithecus specimens, the range of δ15Nenamel values suggests a high degree of individual variability. A larger sample size could further refine understanding of the dietary breadth of Australopithecus.
- Geographic and Temporal Scope: The study is based on samples from Sterkfontein M4 deposits, which are dated to ~3.7 to 3.3 Ma. While the study suggests that the findings may not apply to other Australopithecus populations, this is not a major limitation because the study focuses on this specific group however extension of the methodology to other known groups could be most useful.
- Exclusion of First Molars: While the study acknowledges that first molars may have formed before weaning and be impacted by breast milk, they are not fully excluded from the analysis when calculating the δ15Nenamel range. The researchers note that even when first molars are excluded from the dataset, the δ15Nenamel range of the Australopithecus still exceeds that of any other taxonomic family.
- Inference of Meat Consumption: The study infers a lack of regular meat consumption based on nitrogen isotope data, which is a strong but indirect measure. Though the method is quantitative and robust, there might be more direct evidence that could be explored in future studies such as the presence of cut marks on bones, as mentioned in the introduction.
- Other Animal Resources: The study acknowledges that Australopithecus may have consumed other animal resources, such as insects. The analysis of these resources is complex because they have variable nitrogen isotope values and this could have contributed to the wide range of δ15Nenamel values.
Conclusion
The study makes a valuable contribution to our understanding of Australopithecus diets by providing a robust analysis using a novel methodology. It challenges the traditional view of meat consumption as a primary driver of hominin evolution, and instead highlights the adaptable and opportunistic nature of Australopithecus diets. The study’s methodology offers a new way to explore the dietary ecology of extinct hominins and the onset and intensification of meat consumption in human ancestors. The findings also raise questions about the factors that might have led to the increased meat consumption observed later in hominin evolution. Overall, this study provides compelling evidence that, at least at Sterkfontein M4, Australopithecus were primarily plant-eaters, and that a transition to a meat-rich diet was not a feature of their behavior at this time.
Reference
Lüdecke, T., Leichliter, J. N., Stratford, D., Sigman, D. M., Vonhof, H., Haug, G. H., Bamford, M. K., & Martínez-García, A. (2025). Australopithecus at Sterkfontein did not consume substantial mammalian meat. Science, 387(6743), 155-160. Read Here
Further Reading
Here is a list of scholarly references related to the hominins from Sterkfontein Caves, along with links for further reading:
Journal Articles
- Clarke, R. J. (1998). First-ever discovery of a well-preserved skull and associated skeleton of Australopithecus. South African Journal of Science, 94(10), 460–463. Read More
- Berger, L. R., & Tobias, P. V. (1996). A chimpanzee-sized hominin cranium from Sterkfontein, South Africa, and its implications for hominin evolution. Nature, 376, 563–566.
- Herries, A. I. R., Pickering, R., & Adams, J. W. (2013). A multi-disciplinary seriation of fossil-bearing palaeokarst deposits at Sterkfontein and Swartkrans, South Africa. Quaternary International, 301, 14–24. Read More
- Pickering, R., & Kramers, J. D. (2010). Re-appraisal of the stratigraphy and chronology of Sterkfontein hominid site. Journal of Human Evolution, 59(1), 70–86. Read More
- Granger, D. E., Gibbon, R. J., Kuman, K., Clarke, R. J., Bruxelles, L., & Caffee, M. W. (2015). New cosmogenic burial ages for Sterkfontein Member 2 Australopithecus and Member 5 Oldowan. Nature, 522, 85–88. Read More
- Kuman, K., & Clarke, R. J. (2000). Stratigraphy, artefact industries, and hominid associations for Sterkfontein, Member 5. Journal of Human Evolution, 38(6), 827–847. Read More
- Partridge, T. C. (2005). Dating of the Sterkfontein hominin fossils. South African Journal of Science, 101, 175–180.
Books and Book Chapters
- Tobias, P. V. (1991). Olduvai Gorge Volume 4: The Skulls, Endocasts, and Teeth of Homo habilis. Cambridge University Press. Read More
- Leakey, R. E., & Lewin, R. (1992). Origins Reconsidered: In Search of What Makes Us Human. Doubleday. Read More