Bits of chewed tar discarded by hunter-gatherers in southwestern Scandinavia nearly 10,000 years ago reveal the Stone Age people were affected by tooth decay and gum disease.
A new analysis of DNA found on 3 pieces of birch pitch – made from heated birch bark – excavated in the 1990s in Huseby Klev, Sweden is published in Scientific Reports.
Ancient humans are known to have chewed pitch. They used the heated bark to glue tools together.
More than 100 pieces of pitch were discovered at the site. Previous DNA analysis suggests the humans chewing the tar were both male and female, and aged 5–18 years old. However, other pieces of pitch clearly show adult tooth marks, suggesting ancient humans of all ages and sexes were involved in the toolmaking process.
Dating of the pieces shows they were chewed 9,890–9,540 years ago, the early part of the Neolithic (New Stone Age, 12,000–4,200 years ago).
First, the samples were compared with modern human samples, ancient human dental plaque and a 6,000-year-old chewed tar sample. The researchers found the microbial profile matched, indicating the birch tar was indeed chewed by humans.
But they found a key difference – higher levels of bacteria associated with poor dental health.
It is believed that the ancient ‘chewing gum’ may have had antiseptic and medicinal benefits. Despite this, it probably doesn’t come as a surprise to learn that ancient humans didn’t have quite the same level of oral hygiene that we have today.
The researchers found evidence of gum disease-causing Treponema denticola, Streptococcus anginosus, and Slackia exigua, and tooth decay-causing Streptococcus sobrinus and Parascardovia denticolens.
Relative abundances of the bacteria modelled by machine learning algorithms suggests 70–80% of the hunter-gatherer group was afflicted with gum disease.
The authors suggest that the ancient humans used their teeth for a wide range of tasks including gripping, cutting and tearing. This might have increased their risk of encountering microbial species that cause gum disease and tooth decay.
A wide range of other DNA was found on the chewed-up bits. The researchers identified hazelnut, apple, mistletoe, red fox, grey wolf, mallard, limpet, and brown trout. It’s possible these came from materials chewed by the humans before chewing the tar. These could have come in the form of food, furs and bone tools.
