The first primate look like modern humans, Homo sapiens that is to say was homo erectus, an ancient hominid that evolved in Africa about 2 million years ago. H. erectus was taller than the archaic hominids that preceded it, but they also had longer legs, shorter arms, and larger brains. The timing of their emergence coincides, strangely, with an apparent change in the diets of these ancient peoples – in particular, an increased consumption of meat, giving rise to a hypothesis: Eating meat made us human. But the connection between the carnivore and our skull may be less straightforward than researchers previously thought.
The hypothesis – H. erectus represents a giant leap in the evolution of hominins as a whole, and the concurrent proliferation of meat consumption, as the fossil record suggests, led to a “meat made us human” hypothesis to explain the origins of modern man. Essentially, the theory goes that eating meat fueled the big brains and bodily changes that gave rise to H. sapiens.
Meat is a nutritionally dense food, and generally much more nutritionally dense than plants. Eating it may have given our ancestors the evolutionary edge. Larger bodies with modern proportions, faster and easier digestion, and of course, larger brains are, according to this theory, easily associated with meat consumption. (Of course, not all scientists agreed with this theory.)
But in a new study published this week in the journal Proceedings of the Natural Academy of Sciences, researchers are reanalyzing old data to find that the increase in evidence of meat consumption at archaeological sites may be evidence of a similar increase in archaeological interest – ie. modern scientists have gone looking for evidence of meat consumption – rather than real evidence of a change in our evolutionary timeline. Essentially: The theory that meat made us human may be based on prejudice rather than fact.
What science shows — It is true that the ancestors of modern humans ate meat with plants. Researchers have found “butcher’s marks” on excavated animal bones, dents or scratches where prehistoric hominids likely used stone tools to separate meat from an animal’s skeleton. Butchery marks can be found on fossils 2.6 million years old, so our ancestors probably ate meat at least that long ago.
But around the same 2 million year mark, there seems to be a boom in meat consumption. It’s also when H. erectus appears for the first time in the fossil record. For decades, scientists believed that these two changes were not a simple coincidence, but intrinsically linked: a diet rich in meat allowed homo erectus to evolve its distinctive features, and in turn, homo erectus evolved because hominids ate more meat.
Indeed, that’s what Briana Pobiner, study author and paleoanthropologist at the Smithsonian Museum of Natural History thought.
“I’ve definitely been a purveyor of ‘meat made us human’ hypotheses,” she said. Reverse.
But when Pobiner and his team revisited ancient data from 59 East African archaeological sites dating to between 2.6 and 1.2 million years ago, it turned up empty.
They analyzed the fossils in hundred-year increments, controlling the number of samples at each time using a proxy, and found that the evidence for meat consumption only seems to increase with the number of specimens. representing every moment.
“Sometimes when you have larger fossil samples, you’re more likely to get evidence of meat consumption,” says Pobiner. In other words, the theory can be corrupted by sampling bias – this means that when you look for something, you will probably find it.
With this new analysis, the trend becomes much less clear says Pobiner. And after meat consumption appears in records at 2.6 million years ago, it fluctuates erratically from site to site.
Why is it important – Pobiner was “totally surprised” by the results. Much of his previous research also assumed that the theory was correct.
Pobiner is quick to point out that there is still ample evidence that many of our ancestors ate meat and likely contributed to our evolutionary origins. But she adds that the story is probably more complex than just one thing stimulating the development of modern man.
“There may be more than one factor involved in these big shifts in our evolutionary history,” she says.
Henry Bunn is a paleoanthropologist at the University of Wisconsin-Madison who was not involved in the new research. Bunn agrees with Pobiner on the multifactorial nature of our evolutionary history, but nothing else.
According to him, the meat was never the single determining factor behind the change in development.
“No one is saying that meat is the only engine of human evolution,” Bunn said. Reverse. But if it’s not meat, he posits, then what else?
Theories about the origin of humans beyond meat include the theory that cooking over fire led to more accessible nutrients, that grandmothers helped nurture offspring and therefore allowed for better diets, and that eating insects rather than large animals has helped humans — and our big brains — spring up. But there is no 2 million year old fossil evidence to support any of these ideas.
In Bunn’s view, Pobiner and his co-researchers created a “strawman” by focusing on their estimation of sample intensity. The earliest evidence of meat consumption is found in tiny bone fragments. But a few H. erectus the sites have “50 dead animals depicted, all in a deposit just four inches thick,” Bunn says. He thinks that the early consumption of meat was accidental and random, nothing to do with the regular and coordinated consumption by H. erectus which appears in the fossil record of a few sites after 2 million years. And he points out that the new study erroneously treats all sites uniformly when each has a unique set of conditions that determine the quality of the fossils.
“The effect of this is to add noise to the system,” he says.
Shara Bailey, a biological anthropologist at New York University, who also hasn’t been involved in the recent findings, agrees that meat likely played a critical, but not solo, role in our evolutionary history.
“I think the carnivore plays a role in our becoming human,” Bailey said. Reverse. “This becomes a widespread pattern later in the Pleistocene. It was probably more important in some periods and populations than others.
And after – Pobiner admits the research has limitations, including the assumptions they had to make about study sites and sampling intensity to run the analysis. “It’s a caveat that bothered us all.” But she’s eager to engage with all comments, including critical responses like Bunn’s. His hope is that the new study will cause anthropologists to question their assumptions, rigorously review existing data, and collect new fossils.
And she also hopes it will cause people outside the field to reconsider the way they think about their diet.
“There are a lot of people who buy into the modern ‘paleo diet’ movements and believe that eating meat has been the most significant dietary change in our evolutionary history,” says Pobiner. But our ancestors were omnivores who ate whatever they had at their disposal.
“I can’t imagine any of our early human ancestors saying, ‘No, I’m not going to eat these tubers. I’m not going to eat these lentils. Food is food.
“I sometimes joke when people say, ‘well, what was the paleo diet?’ That was literally everything.Everything edible in the past went on a paleo diet.
Summary: The appearance of homo erectus shortly after 2.0 Ma is widely regarded as a turning point in the evolution of the human diet, with increased consumption of animal tissue leading to the evolution of larger brains and body size and reorganization of the ‘intestine. An increase in the size and number of zooarchaeological assemblages after the appearance of H. erectus is often held up as a centerpiece of archaeological evidence for increased carnivory in this species, but this characterization has yet to be examined in detail. Any generalized dietary change leading to the acquisition of key traits in H. erectus should be persistent in zooarchaeological records over time and can only be convincingly demonstrated by large-scale analysis that transcends individual sites or localities. Here we present a quantitative synthesis of the zooarchaeological records of East Africa from 2.6 to 1.2 Ma. fossil record, which limits the archaeozoological visibility of the hominin carnivore. When correcting for sampling effort, there is no sustained increase in the amount of evidence for hominid carnivory between 2.6 and 1.2 Ma. Our observations have undermined the evolutionary narratives linking the anatomical and behavioral traits to increased meat consumption in H. erectus, suggesting that other factors are likely responsible for the appearance of his human traits.