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Evolution: Did eating meat really make us human? | Science & Tech



Human activity has been dictated by the past for thousands of years. In a world full of uncertainties, tradition offers certainty and the voice of our ancestors is a source of authority. In The Last Whalers, Doug Bock Clark’s excellent account of Indonesia’s Lamaleran tribe, the author describes how a council of wise men interprets what the tribes’ ancestors might say – from beyond the grave – about the incorporation of technological innovations for hunting sperm whales. Inhabiting a village on the remote island of Lembata – one of the last on the planet to resist progress – the tribesmen jump from oar-powered whaling boats to harpoon their prey. The council decides whether their ancestors would consider motorboats suitable for approaching the whale or whether they can be used to catch lesser animals such as rays or dolphins. If the tribe pushes hard enough, the ancestors’ views can be made to shift.

Around the world, nations and their rulers have interpreted moments in history to back their goals, such as the foundation of Kievan Rus’, a medieval federation of eastern and northern European nations, to cement the link between Ukraine and Russia. And although the reconstruction of the past is now carried out scientifically, greater objectivity has not diminished the past’s role in propping up current positions. Human evolution, for example, is now used to justify the Paleolithic diet, the need for a more egalitarian society and the benefits of running. If paleontologists say that our ancestors did it 500,000 years ago, it is assumed that it is stitched into our DNA and, therefore, must be good for us now.

Towards the end of January, the scientific journal Proceedings of the National Academy of Sciences (PNAS) published an article that tried to undermine the popular belief regarding a key moment in human evolution. About two million years ago, a hominid emerged that began to look very much like us. Homo erectus walked and ran completely upright and had a large brain – much larger than that of their ancestors. The brain is known to be a very useful but high-maintenance tool. Although it constitutes only 2% of our body mass, it consumes a quarter of our daily energy and uses almost 10 times more energy than muscle when at rest. To support this organ, a concentrated source of energy is needed, and meat would have been perfect for the job. A multitude of zooarchaeological sites confirm that Homo erectus hunted animals and cut them up for eating, which led to the hypothesis that eating meat made us human.

Written by a research team led by W. Andrew Barr, an assistant professor of anthropology at George Washington University in the US, the PNAS paper challenges this long-held view. Although the evidence shows a dramatic increase in meat consumption after the appearance of Homo erectus, Barr believes that this is because of an increase in sampling intensity. Paleontologists set out to find some concrete evidence of meat consumption in East Africa, which is considered the cradle of humankind, and that’s what they found.

However, after collecting data from the region from between 2.6 and 1.2 million years ago, Barr and his team observed that, when the variation in sampling effort over time is taken into account, the increase in meat consumption was not significant. “Our observations undercut evolutionary narratives linking anatomical and behavioral traits to increased meat consumption in H. erectus, suggesting that other factors are likely responsible for the appearance of its human-like traits,” says the study.

I think this study and its findings would be of interest not only to the paleoanthropology community, but to everyone who currently bases their dietary decisions on some version of this carnivore narrative

W. Andrew Barr, assistant professor at George Washington University

Paleontologists are aware that their findings are often used as ammunition in contemporary debates, such as whether we should eat less meat, but they do not usually state their results with such explicit reference to the narrative. In his university press release, Barr was even more direct: “I would think this study and its findings would be of interest not just to the paleoanthropology community but to all the people currently basing their dieting decisions around some version of this meat-eating narrative.” Clearly, the researcher is aware of his potential to establish narratives that might change the present thanks to the influence of all things atavistic.

Barr and his team gathered already-published data from nine areas where major research has been carried out in East Africa, including 59 site levels dating between 2.6 and 1.2 million years ago. They used several methods of quantitative assessment to track the link between our ancestors and meat consumption, such as the number of zooarchaeological sites that have examples of animal bones bearing cut marks made by stone tools and the total count of cut-marked animal bones at the sites. The research states that while the volume of modified bones clearly increased after the appearance of Homo erectus, there was a corresponding increase in sampling intensity, suggesting that intensive sampling, rather than changes in human behavior, might have given rise to the theory.

Narratives in science are a powerful driving force, but some researchers consider that sometimes the data is manipulated to fit the story. Manuel Domínguez Rodrigo, co-director of a research project at Olduvai Gorge, where much of the analyzed remains are located, and also a professor at Madrid’s Complutense University, thinks the result of this study “is crazy.” As one of the most cited authors in the PNAS text as a proponent of the “meat made us human” theory, he says about its authors that “instead of analyzing the taphonomic evidence [the study of the sites and the fossils found in them], they take the variables that suit them to tell their story; the narrative matters more than the evidence.”

Domínguez Rodrigo, considered one of the most experienced researchers working at sites in East Africa, explains that meat consumption cannot be quantified by just taking the presence of cut-marked fossils in the region’s sites as a reference. “There are preservation factors at the sites that make them very different; some are only of hominids, but in most there are several species, and there are other conditioning factors,” he explains. “Articles such as this are the result of archaeologists who do not actually dig at sites from this period but use other people’s data to give free rein to speculation on which to build a career.”

The more in-depth analysis carried out by the Spanish researcher’s team has allowed for the observation of how the behavior of Homo erectus changed over the hundreds of thousands of years studied by Barr. “When you analyze not only the number of bones with cut-marks, but what type of bones they are or what the cuts are like, you can see what was being eaten,” says Domínguez Rodrigo. “You can see that two million years ago they were eating small or medium-sized animals, but then, 1.4 million years ago, they were eating animals ranging from the size of a gazelle to that of a hippopotamus.” Not only does this indicate a more sophisticated hunting ability, it also suggests that the hominid tribes were much larger and could cope with much larger game. At the same time, it suggests that, although there seems to be a greater amount of meat eaten at more recent sites, because there were more individuals needing to be fed the consumption of protein and animal fat would have been the same – details which escape a more superficial analysis.”

“The study is crazy; the narrative is more important than the evidence”

Manuel Domínguez Rodrigo, co-director of a research project at Olduvai

Antonio Rosas, director of the Paleoanthropology Group at the National Museum of Natural Sciences in Madrid, believes that the idea of “doing a large-scale study in both time and space is worthwhile.” However, he also believes that the way in which Barr and his colleagues conducted that study “is superficial, something like a parlor study. It’s not the same thing to see a dead animal and eat the liver, because you’re a scavenger, as it is to hunt it and use all the meat,” he points out. “The amount of meat consumed is totally different.” He is also critical of the initial approach. The first evidence of meat consumption, although controversial, appeared with the Australopithecines – short hominids with a brain little bigger than that of a chimpanzee, but who were already walking upright more than three million years ago. The consumption of meat appeared without a doubt with Homo habilis, who lived between 2.3 to 1.65 million years ago, and increased with Homo erectus. That is the moment when meat would have made us human.

Rosas believes that this pattern is clear and that it is not even necessary for there to be an increase in meat consumption during the period analyzed by Barr and his colleagues for its role to be fundamental in our history. “In the evolution of Homo erectus, between two and one million years ago, there is a period of evolutionary equilibrium; when 850 cubic centimeters of cranial capacity is exceeded, an equilibrium is reached,” he says. That leap would be due to meat consumption, which would explain part of what made us human, and its effects are maintained with that same level of consumption over hundreds of thousands of years.

The next major turning point in human evolution occurred a little over half a million years ago, with the increase in the brain size of species such as Homo heidelbergensis in Europe and Homo rudolfensis in Africa. This increase is usually explained by the widespread use of fire and the cooking of food, which, like the initial meat consumption, would multiply the amount of nutrients that can be obtained from meat by reducing the energy used in the digestive system and freeing it for the brain. “The authors discuss alternatives to the theory that meat made us human such as new ways of preparing food using fire,” says Rosas. “But fire becomes widespread hundreds of thousands of years after the period they analyze.”

Barr acknowledges that “it is likely that meat consumption has had some impact on human evolution.” But he adds that the question is whether meat consumption is specifically linked to Homo erectus. “Our analyses show that […] the idea that there is a widespread and sustained shift towards greater meat consumption at this time is not well supported.”

Regarding Rosas’ approach, which points to the fact that the important change occurs during the appearance of Homo erectus, Barr concedes that, in the period before 1.9 million years, there are not enough sites to know how much meat was consumed, so more information is needed to establish if there really was an increase in meat consumption just before the appearance of Homo erectus.

Scientific methods offers a less direct contact with the voices of our ancestors than that enjoyed by the Lamaleran elders or other ancestral tribes, but it requires no belief in a supernatural connection to the past. Yet the amount of work required to examine our world millions of years ago and the limited amount of available evidence make it tempting to draw conclusions that are far from water-tight.

According to Ana Mateos, a researcher in hominid paleophysiology and ecology at the National Center for Research on Human Evolution (CENIEH) in Burgos, Spain, “sometimes we try to explain very complex aspects of human evolution based on one site or a particular level of a site.” It is a matter of explaining periods of hundreds of thousands of years with a handful of fossils, but regarding Barr’s conclusions, she praises the approach: “It takes into account the need for large sets of data to explain patterns of human evolution; and that these should be analyzed critically to see if what has been assumed to be true for decades still holds, and that’s interesting,” she says, adding that the meat debate is significant “because the plant component in a diet is not preserved as well as the information we can extract from meat consumption by bone marking.”

One of the attractions of the long gone past as a source of certainty is precisely how little is known of it. When one looks at the remote origins of nations or species, the scant pieces of information at our disposal are much easier to organize according to what we would like to believe than a present in which it is difficult to ignore complexity. The latest results do not seem to rule out the importance of meat consumption in that stellar moment of humanity, two million years ago, but the significance of this for humans today will remain debatable. Just as the Lamalerans were pushing their ancestors’ interpreters to accept innovations to make their own lives easier, we will continue to manipulate the interpretations of the paleontologists, our modern-day sages, to justify our current way of life.



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