Neanderthal Brains Grew Larger With Greater Carbohydrate Consumption
Roughly a million years ago, Neanderthal brains doubled in size in about 200,000 years, which is a paltry number in evolutionary terms. For long, brain evolution has been credited to the increasingly sophisticated uses of stone tools. Bigger brains gave Neanderthals new advantages in game hunting, and foraging. These factors have long been known as the main reasons for bigger Neanderthal brains but the latest study on this subject has highlighted another factor in this change in brain size: carbohydrate consumption.
A new study published in the Proceedings of the National Academy of Sciences (PNAS), which studied the oral microbiomes and bacteria from the teeth of Neanderthals and modern humans (prior to the Agricultural Revolution 10,000 years ago), sheds new light on why Neanderthal brains grew in size. The researchers found that starchy and carbohydrate-rich foods, consumed so often that it altered the bacteria in their bodies, changed their behavior and their brain size.
“We think we’re seeing evidence of a really ancient behavior that might have been part of encephalization — or the growth of the human brain,” said Harvard Professor Christina Warinner. “It’s evidence of a new food source that early humans were able to tap into in the form of roots, starchy vegetables, and seeds.” She was quick to point out, that obviously, human beings who were part of this process were not consciously aware of the effect this would have on their brains.
Grauer's gorilla specimens at the Royal Museum for Central Africa in Tervuren (Belgium), showing typical dental calculus deposits on the teeth that are darkly stained, likely as a result of their herbivorous diet, which would have included lots of starches and carbohydrates. (Katerina Guschanski / Royal Museum for Central Africa )
Neanderthal Brains, Dental Plaque, and the Oral Microbiome
The latest study of Neanderthal brains was a major undertaking, comprising a multidisciplinary international research team of 50 scientists, from 13 countries and 41 institutions. The team was primarily led by researchers from the Max Planck Institute for the Science of Human History , Germany and Harvard University.
The study lasted over 7 years as the team painstakingly analyzed the fossilized dental plaque of Neanderthals and Late-Pleistocene to modern humans living over the last 100,000 years, and compared it with that of wild chimpanzees, gorillas and howler monkeys.
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"We were able to show that bacterial DNA from the oral microbiome preserves at least twice as long as previously thought," said J. A. F. Yates. He was the lead author on the study and is currently a doctoral candidate at the Max Planck Institute for the Science of Human History. "The tools and techniques developed in this study open up new opportunities for answering fundamental questions in microbial archaeology, and will allow the broader exploration of the intimate relationship between humans and their microbiome."
The oral microbiome is one of the key indicators of human health, biology and disease. Very little, however, is known about its role in evolution or diversity across varied topographies. In addition, finding billions of DNA sequences and fragments, hundreds of thousands of years old, is a complex and cumbersome process.
Archaeogeneticists have to piece together the broken fragments of ancient genomes , and then, using hi-tech data and technology, they try to understand long-dead bacterial communities. They got lucky with the reconstruction of the 100,000-year-old microbiome of a Neanderthal from Pešturina Cave in Serbia, doubling the age of the previously oldest oral microbiome reconstructed.
Closeup of an aboriginal Neanderthal caveman skull clearly showing teeth, and dental plaque, which was used to understand the oral microbiome and Neanderthal carbohydrate consumption. ( gerasimov174 / Adobe Stock)
Neanderthal Brains And Tooth Bacteria Poorly Researched
The other challenge is that this area of study is surprisingly poorly researched in terms of naming the millions of bacteria that live in our mouths. A lot of the oral microbiomes are responsible for vital functions within the human mouth, including healthy gums and teeth. Yet most of these bacteria remain unnamed, which poses fundamental challenges for contemporary researchers.
The communities of bacteria in the mouths of pre-agricultural modern humans and Neanderthals strongly resembled each other, as per the study. In particular, modern humans and Neanderthals harbored an unusual group of Streptococcus bacteria in their mouths. Streptococcus has the unique ability to bind to an abundant enzyme in human saliva called amylase, an enzyme that catalyzes the hydrolysis of starch into sugar.
The sugar consuming bacteria was found in the plaque DNA of Neanderthals and modern humans, pointing to definite starch consumption . Chimpanzees, on the other hand, do not have any strep bacteria on their teeth. Additionally, the streptococcus presence in both Neanderthals and early humans suggests an inheritance of microbes from common ancestors, potentially 600,000 years ago.
Family of Neanderthals or early Homo Sapiens cooking. The latest study shows that it wasn't only meat on the menu but also rising amounts of carbohydrates, which contributed to brain size expansion. ( Gorodenkoff / Adobe Stock)
Human Evolution and Microbiomes
The consequences of this, in the study of human evolution , are profound and four-fold.
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First, the big brain expansion theory , which had been centered around stone-tool development and meat consumption has had its scope expanded for future research.
Second, as Christina Warriner from Harvard University, a molecular archaeologist and co-author on the study, puts it, “…this pushes the importance of starch in the diet further back in time.”
Third, the presence of the amylase enzyme, which aids cooked food digestion efficiency, also points to cooking becoming common and widespread by about 600,000 years ago. This helps dispel the notion that cooking, as we know it, was synonymous only with the Agricultural Revolution, which is a much more recent phenomenon. Going forward, the question is whether cooking was part of the big-brain expansion around 2 million years ago, but the jury is still out on that.
Finally, the study has helped enhance our knowledge of microbiomes and make their study a serious proposition for current and future historians. As Warriner succinctly says, ““It shows that our microbiome encodes valuable information about our own evolution that sometimes gives us hints at things that otherwise leave no traces at all.”
Top image: Neanderthal brains and modern human brains are different but what is really interesting is how increasing carbohydrates in the Neanderthal diet increased brain size. The skull in the foreground is a Neanderthal and the smaller one in the background is a modern human skull. Source: Bruder / Adobe Stock
By Rudra Bhushan
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Wehner, M. 2021. Neanderthals had huge brains and ate a lot of carbs . Available at: https://bgr.com/science/neanderthal-diet-homo-sapiens-5924881/.
Yates, J.A.F., Velsko, I., et. al . 2021. The evolution and changing ecology of the African hominid oral microbiome . PNAS, 118. Available at: https://doi.org/10.1073/pnas.2021655118.