A recent study conducted by researchers at Trinity College Dublin delves into the ancient past through the examination of 4,000-year-old teeth, shedding light on the evolution of human diets over the centuries. 

These teeth, remarkably preserved and recovered from an Irish limestone cave, provide insights into the oral microbiomes of our ancestors during the Bronze Age.

4,000-year-old Teeth Unlocks Ancient Secrets

Collaborating with archaeologists from Atlantic Technological University and the University of Edinburgh, the team conducted genetic analyses, uncovering significant changes in the oral microenvironment over millennia.

Of particular interest was the identification of various bacteria associated with gum disease, along with the retrieval of the first high-quality ancient genome of Streptococcus mutans, a key contributor to tooth decay. 

While S. mutans is prevalent in modern mouths, its rarity in ancient genomic records suggests potential factors such as its acid-producing nature, which may hinder fossilization.

Moreover, the introduction of sugary foods in recent centuries likely contributed to an increase in dental cavities, contrasting with the more gradual uptick observed after the adoption of cereal agriculture thousands of years ago.

Excavated from Killuragh Cave, County Limerick, the teeth belonged to the same male individual, offering a snapshot of his oral health. Despite showing no visible cavities, one tooth exhibited a significant abundance of S. mutans DNA, indicating a potential predisposition to cavities.

The study also highlighted disruptions in the natural balance of the oral microbiome, with S. mutans outcompeting other streptococcal species. This imbalance may have contributed to the pre-disease state observed in the individual.

Furthermore, the researchers explored the "disappearing microbiome" hypothesis, which posits that modern microbiomes are less diverse than those of our ancestors. 

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A Look into the Ancient Mouth

The analysis of Bronze Age teeth revealed highly divergent strains of Tannerella forsythia, a bacteria associated with gum disease, emphasizing the importance of understanding biodiversity loss and its implications for human health.

Notably, very few full genomes from oral bacteria have been recovered prior to the Medieval era. By examining prehistoric diversity, the researchers unveiled significant changes in the oral microenvironment over time.

In particular, they observed a single lineage of T. forsythia becoming dominant worldwide over the last 750 years, suggesting natural selection at play. Similarly, S. mutans populations have undergone recent lineage expansions and changes in gene content related to pathogenicity, coinciding with humanity's increased sugar consumption.

The researchers attributed these changes to differences in evolutionary mechanisms shaping genome diversity in these species. Despite the dramatic transformations observed from the Bronze Age to today, recent cultural transitions in the industrial era appear to have had a profound impact on disease-causing bacteria.

"These strains from a single ancient mouth were more genetically different from one another than any pair of modern strains in our dataset, despite the modern samples deriving from Europe, Japan and the USA," Iseult Jackson, a PhD candidate at Trinity, and first author of the study, said in a press release statement.

"This represents a major loss in diversity and one that we need to understand better." 

The findings of the team were published in the journal Molecular Biology and Evolution. 

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