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Isotope analyzes performed on single amino acids in Neanderthals' collagen samples shed new light on their debated diet – ScienceDaily



Neanderthals are highly debated: they are traditionally considered carnivores and hunters of large mammals, but this hypothesis has recently been challenged by numerous pieces of evidence of plant consumption. Ancient diets are often reconstructed using nitrogen isotope ratios, tracer of the trophic level, the position of organism occupies in a food chain. Neanderthals are apparently occupying a high position in terrestrial food chains, exhibiting slightly higher ratios than carnivores (like hyenas, wolves or foxes) found at the same sites. It has been suggested that these slightly higher values ​​were due to the consumption of mammoth or putrid meat. And we also know some examples of cannibalism for different Neanderthal sites.

Paleolithic modern humans, which had recently disappeared in France after the Neanderthals, exhibited even higher nitrogen isotope ratios than Neanderthals. This is classically interpreted as the signature of freshwater fish consumption. Fishing is supposed to be a typical modern human activity, but again, a debate exists whether or not Neanderthals were eating aquatic resources. When Klervia Jaouen, a researcher at the Max Planck Institute for Evolutionary Anthropology and first author of the study, and collaborators discovered high nitrogen isotopes in the collagen of two Neanderthals falling in the range of modern humans, they wondered whether this could be a signature of regular fish consumption.

The Neanderthals come from Les Grands du Renne, in France, two sites where no fish remains have been found. However, the measurements were performed on a tooth root, which recorded the diet between four to eight years of the individual's life, and on a bone of a one-year-old baby. These high nitrogen isotope ratios also indicate that the Neanderthals were not present at this age, contradicting in the case of the Les Cotton Neanderthal (the one whose tooth root was analyzed) forms pieces of evidence of early weaning around one year of age. In other words, many explanations (eg freshwater fish consumption, putrid meat, late weaning or even cannibalism) could account for such high values, and identifying the factor could change our understanding of Neanderthals' lifestyles.

Analysis of amino acids

In order to explain these exceptionally high nitrogen isotopic ratios, Jaouen and collaborators decided to use a novel isotope technique. Compound-specific isotopic assays (CSIA) allow to separately analyze the amino acids contained in the collagen. Some of the amino acid isotopes are influenced by environmental factors and the isotopic ratios of the food eaten. Other amino acid isotope ratios are influenced by the trophic level. The combination of the amino acid isotope ratios allows to decipher the contribution of the environment and the trophic level to the final isotope composition of the collagen.

"Using this technique, we discovered that the Neanderthal or Les Cottés had a purely terrestrial carnivore. diet: she was not a late weaned child or a regular fish eater, and her people seem to have mostly hunted reindeers and horses, "says Jaouen. "We also confirmed that the Grotte du Renne Neanderthal was a breastfeeding baby whose mother was a meat eater." Interestingly, this conclusion matches with the observations of the zoocheologists.

The study also illustrates the importance of this new isotope technique for future investigations into ancient human and Neanderthal diets. Using compound-specific isotope analysis allowed the researchers not to misinterpret the global nitrogen isotope ratio which was exceptionally high. Michael P. Richards of the Simon Fraser University in Canada comments: "Previous isotope results in a mainly carnivorous diet for Neanderthals, which matched the extensive archaeological record of animal remains found and deposited by Neanderthals. There has recently been some frankly bizarre interpretations of the bulk isotope data ranging from Neanderthals primarily subsisting on aquatic plants to eating each other, both in direct contrast to the archaeological evidence. These new compound-specific isotopes confirm earlier interpretations of Neanderthal diet as being composed of mainly large herbivores, although of course they also consumed other foods such as plants. "

Monotonous diet

In addition to confirming the Neanderthals as terrestrial carnivores, this work seems to indicate that these hominins had a very monotonous diet over time, even once they had started to change their material industry, possibly under the influe nce of modern humans. The baby Neanderthal or Grotte du Renne was indeed found to be associated with Châtelperronian, a lithic technology similar to that of modern humans. Late Neanderthals were therefore very human, painting caves and wearing necklaces, but unlike their sister species, did not seem to enjoy fishing.

Jean-Jacques Hublin, director of the Department of Human Evolution at the Max Planck Institute for Evolutionary Anthropology, comments: "This study confirms that when Homo sapiens arrived in Europe and with Neanderthals, they were in direct competition for the exploitation of large mammals." "The systematic use of the combination of CSIA and radiocarbon dating will help to understand if the two species had the same subsistence strategies during those crucial times," concludes Sahra Talamo, a researcher at the Leipzig Max Planck Institute.


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