Dental Plaque Reveals Pre-Agriculture Plant Food For Humans

This is one of the three richest Late Meroitic graves identified at the cemetery, that of a young male. Credit: Donatella Usai/Centro Studi Sudanesi and Sub-Sahariani (CSSeS)

Ah, dental plaque. That pesky buildup that causes your dentist to engage in futile conversations about flossing every 6 months is helping researchers determine how our prehistoric human ancestors utilized plants that are now regarded as nuisance weeds within their diets. The research was led by Karen Hardy of the University of York and the results were published in PLOS ONE.

The prehistoric site Al Khiday in Central Sudan represents a span of 7000 years, including burial grounds during the pre-mesolithic, neolithic, and meroitic periods. Hardy and her team collected and analyzed calcified dental plaque known as calculus from 19 individuals. They were able to determine that during pre-agricultural times, these ancient people dined on Cyperus rotundus; a grass-like plant that forms small tubers underground. The plant is now commonly regarded as a weed and is known as purple nut sedge.

"Purple nut sedge is today considered to be a scourge in tropical and sub-tropical regions and has been called the world's most expensive weed due to the difficulties and high costs of eradication from agricultural areas. By extracting material from samples of ancient dental calculus we have found that rather than being a nuisance in the past, its value as a food, and possibly its abundant medicinal qualities were known. More recently, it was also used by the ancient Egyptians as perfume and as medicine.” Hardy explained in a press release

"We also discovered that these people ate several other plants and we found traces of smoke, evidence for cooking, and for chewing plant fibers to prepare raw materials. These small biographical details add to the growing evidence that prehistoric people had a detailed understanding of plants long before the development of agriculture.”

There was evidence of these people eating purple nut sedge from all time periods studied at Al Khiday, indicating that it must have been a very important food source in the region. Even after agriculture had been introduced, they still consumed the plant. The purple nut sedge could have had quite a bit to offer.

The properties that make the plant such a pest as a weed would have been highly revered among those depending upon it. It grows and reproduces very quickly, providing a good supply. Additionally, the plant can inhibit the bacterium Streptococcus mutans, which is one of the chief factors involved in tooth decay. The team noticed that the rate of dental cavities within the human remains was incredibly low. It could very well be that part of the appeal of consuming the plant was that it may have acted like a natural toothbrush, keeping the teeth healthy and strong, long before dental hygiene was introduced. 

It has been traditionally assumed that humans mostly relied on an animal-based diet prior to the introduction of agriculture. However, this study shows that the people of Al Khiday ate plants in a variety of ways. The techniques used to identify the traces of purple nut sedge could be applied to other remains in other locations, possibly re-writing the book on the dietary habits of prehistoric people and give a greater understanding of the history of agriculture.

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