Study explains early humans ate starch — and why it matters

The scientists analyzed the fossilized dental plaque of both modern humans and Neanderthals and compared them to those of humanity’s closest primate relatives, chimpanzees and gorillas, as well as howler monkeys, a more distant relative.

Using newly developed tools and methods, they genetically analyzed billions of DNA fragments preserved in the fossilized plaque to reconstruct their genomes. It’s similar in theory to how archeologists painstakingly piece together ancient broken pots, but on a much larger scale.

The biggest surprise from the study was the presence of particular strains of oral bacteria that are specially adapted to break down starch. These strains, which are members of the genus Streptococcus, have a unique ability to capture starch-digesting enzymes from human saliva, which they then use to feed themselves. The genetic machinery the bacteria uses to do this is only active when starch is part of the regular diet.

Both the Neanderthals and the ancient humans that scientists studied had these starch-adapted strains in their dental plaque while most of the primates, who feast almost exclusively on non-starchy plant parts, like fruits, stems, and leaves, had almost no streptococci that could break down starch.

“It seems to be a very human-specific evolutionary trait that our Streptococcus acquired the ability to do this,” Warinner said.

The findings also push back on the idea that Neanderthals were top carnivores, given that the “brain requires glucose as a nutrient source and meat alone is not a sufficient source,” Warinner said.

Researchers said the finding makes sense because for hunter-gatherer societies around the world, starch-rich foods — roots, tubers (like potatoes), and forbs, as well as nuts and seeds, for example — are important and reliable nutritionsources. In fact, starch currently makes up about 60 percent of calories for humans worldwide.

“Its availability is much more predictable across the annual season for tropical hunter-gatherers,” said Richard W. Wrangham, Ruth B. Moore Professor of Biological Anthropology and one of the paper’s co-authors. “These new data make every sense to me, reinforcing the newer view about Neanderthals that their diets were more sapiens-like than once thought, [meaning] starch-rich and cooked.”

The research also identified 10 groups of bacteria that have been part of the human and primate oral microbiome for more than 40 million years and are still shared today. While these bacteria may serve important and beneficial roles, relatively little is known about them. Some don’t even have names.

Focusing on Neanderthals and today’s humans, the analysis surprisingly showed the oral microbiomes of Neanderthals and today’s humans were almost indistinguishable. Only when looking at individual bacterial strains could they see some differences. For example, during the Ice Age, ancient humans living in Europe before 14,000 years ago shared some bacterial strains with Neanderthals that are no longer found in modern humans.

The differences and similarities from the study are all part of what makes us human, Warinner said. It also touches on the power of analyzing the tiny microbes that live in the human body, she said.

“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,” Warinner said.

This work was partially supported by the National Science Foundation, the National Institutes of Health, the European Research Council, the German Research Foundation, the National Research Foundation of South Africa, the Czech National Institutional Support, Science and Technological Development of the Republic of Serbia, the Swedish Research Council Formas, the Werner Siemens Foundation, and the Max Planck Society.