Revelation on the resistance to caries of prehistoric men, thanks to a study of 4000 year old teeth

Brushing, flossing and mouthwash won’t change anything. The rate of dental caries remains high in our contemporary societies. However, our distant ancestors – although less equipped – suffered much less. A rare discovery is now helping scientists better understand how changes in our diet have contributed to this prevalence.

Archaeologists have in fact identified and studied two teeth from an individual who lived 4,000 years ago, during the Bronze Age. However, his two molars contained bacteria, responsible for dental caries and gum disease, and above all particularly informative, as described in an article in the journal Molecular Biology and Evolution, published on March 27, 2024.

Rare DNA analysis of bacteria associated with cavities

The two teeth were more precisely unearthed during excavations of a limestone cave in County Limerick (southwest of Ireland), carried out between 1993 and 1996. Their analysis revealed that they both came from the same adult man, having lived between 2280 and 2140 BC. AD

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At the kung fu nuns’ convent

It also showed that they had a surprising abundance of oral bacteria Streptococcus mutans, often associated with tooth decay in humans. The individual’s enamel was not damaged, however, this bacterial presence in such quantities suggests that he would undoubtedly have developed cavities if he had lived longer, according to the researchers.

Several other teeth found at the same site showed signs of decay. But the skeletal remains having been found disarticulated and separated from each other, archaeologists do not know whether these remains come from the same person or other members of his community.

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Regardless, such a profusion of S. mutans is astonishing. The organism is rare in the ancient genomic record: due to its acidogenic nature, causing the degradation of tooth DNA, it does not store well. Furthermore, the researchers suspected that S. mutans is not commonly found in ancient enamel due to the human diet, once less rich in refined sugars and processed foods before the start of agriculture.

This would explain why the bacteria was only discovered in very small quantities and in a few rare remains: a Neolithic tooth dated between 3400 and 2900 BC. BC, discovered in the south-west of France; a Scandinavian Mesolithic “chewing gum”, dated between 9890 and 9540 BC. AD

More sugar, more S. mutansno more cavities

The authors of the research presented here cannot explain why the bacteria spotted on the newly deciphered teeth were so well preserved. The cool, dry conditions of Ireland’s Killuragh Cave were surely key factors.

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Their comparison with modern samples nevertheless revealed that the ancient evolutionary tree of S. mutans is more complex than they initially imagined. It also confirmed that its characteristics, such as its virulence (ability to cause harm), had evolved alongside changes in human diets.

The phylogenetic analysis of S. mutans old compared to that of S. mutans modern has finally “revealed a major change in recent centuries linked to an increase in sugar consumption”which would have created a favorable habitat for the species in the oral microbiome, summarize the scientists.

“[Elle] indicates significant post-medieval population expansions for [la bactérie]highlighting the outsized impact of recent dietary changes”they write.

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A finding that supports those of previous studies, where higher rates of cavities were observed with the greater availability of refined sugar in the 19th century, for example, Louise Humphrey, research director at the Center for Research on Sugar, told CNN. Human Evolution from the Natural History Museum in London (England), which did not participate in the latest study.

More generally, observations of cavities on old teeth became much more frequent after the adoption of cereal agriculture (wheat, barley) around 10,000 years ago.

A loss of biodiversity deemed “worrying”

Still other research, published in Nature Genetics in 2013 and carried out using the tooth enamel of 34 prehistoric skeletons, had already highlighted the fact that as our diet has evolved, the composition of the bacteria in our mouth had done the same. However, in this transition, certain types of pathogenic bacteria that are particularly fond of the new carbohydrates have begun to prevail over other types of more “friendly” bacteria.

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S. mutans is the perfect example, because it has an advantage over other bacteria of its kind, add the experts: it is capable of metabolizing the sugars of foods trapped in the teeth to produce acids – responsible for cavities – which allows it to “prosper”.

The presence of another organism, here identified in the two Bronze Age teeth, is just as significant: Tannerella forsythia, bacteria involved in gum disease (periodontitis). If it is more commonly found in ancient genomic records, scientists have observed two distinct strains here, compared to only one today.

This therefore suggests that at least 4,000 years ago, prehistoric oral microbiomes were more diverse than modern microbiomes. This loss of bacterial biodiversity is worrying, according to specialists at Trinity College Dublin, because it could have negative impacts on human health.

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Lara Cassidy, assistant professor in the department of genetics at Trinity College Dublin (Ireland) and lead author of the study, concludes:

The last few centuries have seen an incredible change in human diet. Particularly understanding how this has impacted the microbiome, not just the oral microbiome, but also the gut microbiome, might help us understand a little bit about why certain diseases have become so prevalent in Western or Westernized populations over the last few centuries.