Study Dispels Human Meat Diet Hypothesis, Changing Evolutionary Story
In developed societies across the world today, many are converting to vegetarianism or veganism, following diets that completely exclude meat or animal products from their consumption habits. Over the course of human history, frequent meat eating has been associated as a distinctive marker between humans and other primates. However, a new study published in the journal Proceedings of the National Academy of Sciences (PNAS) actually shows that the human meat diet hypothesis has been overstated in early human evolution, questioning the hard-wiring of humans to be carnivores “by nature.”
Dr. W. Andrew Barr, an assistant professor of anthropology at the George Washington University, and lead author on the current study remarked:
“It’s clear that eating meat has been important for many groups of humans throughout much of human history and prehistory. But the idea that there was a sudden evolutionary event where meat eating went from being relatively unimportant to being so central that it drove the evolution of key human traits just doesn’t shake out in our analysis of the published evidence.”
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Reconstruction of the Homo erectus Turkana boy of Kenya with light clothing by Adrie and Alfons Kennis at the Neanderthal Museum. (Neanderthal Museum / CC BY-SA 4.0)
Homo Erectus and the Human Meat Diet Hypothesis
The widespread belief has been that with the advent and arrival of Homo erectus, literally, upright man, roughly 2 million years ago, and the increase in the brain size, an evolutionary transition was made towards more human-like traits, leading to a major dietary shift that increasingly was a meat diet. Popularly known as the “meat made us human” hypothesis, the authors of the new study argue that greater evidence skewed in favor of this theory has created a narrative not necessarily based on historical evidence.
Homo erectus in East Africa surrounded by contemporary fauna suggesting the meat diet was everything from a certain point on. But the latest study completely rewrites this evolutionary diet hypothesis. (Mauricio Anton / GWU)
The assemblage of data on this study has been extremely comprehensive. Nine major research areas in eastern Africa were chosen (where the first humans emerged), including shortlisting 59 site levels dated between 2.6 and 1.2 million years ago. Within this, further subdivisions were created based on specificities: zooarchaeological sites with animal bones that display incisions created by stone tools, the total number of animal bones with cut marks across all sites, and the number of separately reported stratigraphic levels, reports Cosmos Magazine.
Dr. Barr said, “Generations of paleoanthropologists have gone to famously well-preserved sites in places like Olduvai Gorge looking for—and finding—breath-taking direct evidence of early humans eating meat, furthering this viewpoint that there was an explosion of meat eating after 2 million years ago. However, when you quantitatively synthesize the data from numerous sites across eastern Africa to test this hypothesis, as we did here, that ‘meat made us human’ evolutionary narrative starts to unravel.”
Cut marks on herbivore remains from prehistoric times can tell us a lot about how much meat was consumed by humans as they evolved. (Scientific Reports)
A Sampling Bias Leading to Skewed Data Interpretation?
Their hypothesis about skewed data turns out to be correct. There is no clear indication about a sustained increase in relative amount of data to support carnivorous human behavior after the arrival of the Homo erectus. In raw data terms, while there is an overall increase in the number of modified bones found at these sites, the numbers correspond with an increase in sampling intensity, rather than a historical or evolutionary change or deviation in food habits.
This points to a sampling bias, rather than an evolutionary alteration, reports NBC News. This is essentially a product of excavating samples from associated sites, and subsequent time periods, almost creating a looping pattern of confirmation bias.
"I've excavated and studied cut marked fossils for over 20 years, and our findings were still a big surprise to me," Briana Pobiner, a research scientist in the Human Origins Program at the Smithsonian's National Museum of Natural History and co-author on the study, said. She also stated:
"This study changes our understanding of what the zooarchaeological record tells us about the earliest prehistoric meat-eating. It also shows how important it is that we continue to ask big questions about our evolution, while we also continue to uncover and analyze new evidence about our past."
The increase in hominin cranial capacity over time. (Encyclopædia Britannica, Inc. / CC BY-SA 4.0)
Flaws With the Methodology and Moving Forward
This study is not without its flaws. Competing theories and criticisms of the current study methodology exist. For example, why is brain size a defining feature of H. erectus when recent evidence has pointed to an overlap in brain sizes and definition between the H. erectus, H. habilis, and H. rudolfensis. In fact, it was only in the latter half of the H. erectus evolutionary stage that they developed larger brains.
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Additionally, brain size is not exclusively linked to meat across carnivores. Baboons for example, have larger brains if they live in larger social groups, as per a 2021 study published in Evolutionary Biology. Here, the authors wrote, rather crucially, “the notion that relative brain size validly represents selection on brain size relies on the untested assumptions that brain-body allometry is restrained to a stable scaling relationship across species and that any deviation from this slope is due to selection on brain size.”
While it is true that the H. erectus does display a smaller molar size compared to the other species mentioned above, this is perhaps an indication of a diet that was no longer primarily plant based.
As with any study of human origins, the story must continue, and for that, more research and analysis are needed. What cannot be denied, however, is that as we face a new present with human beings willingly choosing to not eat meat and animal-based products, our predecessors were conversely learning the benefits of adding more meat to their diet.
Top image: These 1.5 million year old fossil bones with cut marks from Koobi Fora, Kenya were used in the latest study to understand the evolution of the human meat diet, which revealed that the story is more complex and less meaty. Source: Briana Pobiner / GWU
By Sahir Pandey
Barr, W.A., Pobiner, B., et al. 2022. No sustained increase in zooarchaeological evidence for carnivory after the appearance of Homo erectus. PNAS, 119 (5). Available at: https://doi.org/10.1073/pnas.2115540119
Kiefer, P. 2022. Eating meat may not have been as crucial to human evolution as we thought. Available at: https://www.popsci.com/science/eating-meat-human-evolution-study/
Phiddian, E. 2022. Did meat eating really play a big role in human evolution? Available at: https://cosmosmagazine.com/history/palaeontology/meat-eating-human-evolution-important/
Sloat, S. 2022. Did eating meat make us human? New research casts doubt. Available at: https://www.nbcnews.com/science/science-news/eating-meat-make-us-human-new-research-casts-doubt-rcna13315
George Washington University. 2022. New Study Calls Into Question the Importance of Meat Eating in Shaping Our Evolution. Available at: https://mediarelations.gwu.edu/new-study-calls-question-importance-meat-eating-shaping-our-evolution