About 600 million people today chew on betel nuts —- the brownish green seeds of certain palm trees that are about the size of a walnut. Betel nut users say they get all kinds of benefits — relief from indigestion, fresh breath, an energy boost.
The medical community notes that long-term betel nut use can damage teeth, increase the risk of heart disease, and lead to oral cancer due to the chemicals within.
Still, many people in Asia and the Asian Pacific are addicted to chewing them. Betel nuts are considered the world's fourth most commonly used mind-affecting substances, after tobacco, alcohol and caffeine.
A new study, published in Science Advances, finds this love affair with betel nuts is nothing new. In fact, it's likely very, very old. By looking at ancient teeth, researchers uncovered what they think is an early stage in the practice, when hunter-gatherers had a habit of sucking on betel nuts, possibly for their painkilling effects.
"It's a chance archaeological discovery that reveals an initial stage in the development of this common drug used today," says Adam Brumm, a professor of archaeology at Griffith University in Australia who led the research, "We think it might have started with hunter-gatherers just sucking on the nuts, almost as though they were gobstoppers."
Outside researchers find the evidence compelling though not conclusive — and further note that drug use has longstanding and deep roots among humanity: The instinct to experiment and expand our horizons with substances is part of human nature, says José Capriles, associate professor of anthropology at Penn State University, who has found drugs used by humans a thousand years ago in South America.
Puzzled by "strange grooves"
How did scientists uncover this ancient betel nut usage? The answer involves two puzzling sets of teeth, fake saliva — and some personal experimentation.
On an archaeological dig in Sulawesi, an island in modern-day Indonesia, Brumm and his colleagues excavated some very old human remains.
They belonged to a hunter-gatherer who lived as far back as 25,000 years. The remains posed a mystery. "There were really strange grooves in the teeth that we couldn't explain," Brumm says.
He emailed other archaeologists — "all of the world's leading experts in ancient dental wear" — soliciting their advice. "None of them could explain how these grooves could have formed," says Brumm.
About 20 miles to the east, they found a second set of teeth from a human who lived up to 8,000 years ago, with similar marks. "The grooves were so deep that they had actually exposed the pulp cavity, the nerve center, of several teeth," Brumm says, describing it as a pattern that likely took decades of repeated wear to form.
While hunter-gatherers from that time are known to have used their teeth as tools — holding, breaking, stretching things — none of those uses matched the grooves on these teeth. "We ruled out any type of food they might have been eating, we ruled out the possibility that they were processing plant fibers to make string in their mouth," says Brumm.
Brumm was stumped. Then he remembered another example of distinctive teeth wear, from the colonial period in Europe, America and Australia, when laborers habitually smoked tobacco from clay pipes. "They would have the pipe sticking out of their mouth, Popeye-style," Brumm explains, "Over a lifetime of this habit, they've got a perfectly round notch in their teeth that you can slot the clay pipe stem straight into."
Brumm and his colleagues thought the teeth grooves from Indonesia might originate in a similar habit, one grounded in cultural practices.
The case for the betel nut
In the Asia and Pacific region today, betel nuts are commonly chewed with other chemicals for their combined stimulant effects.
However, the wear patterns on the teeth were consistent with sucking — not chewing — hard, round abrasive objects over many years, Brumm says. He and his colleagues think they've uncovered an early developmental stage in the practice. "We think they were hooked on nut-sucking," Brumm says. Since sucking betel nuts is not common today, Brumm partnered with Professor Roger Papke, a neuropharmacological researcher at the University of Florida, to test whether the action could cause a drug effect ancient humans may have desired.
"We soaked whole betel nuts in artificial saliva, and then introduced the resultant extracts into frog egg cells engineered to produce human brain receptors," Brumm says. They found that the artificial saliva successfully extracted arecoline, an active chemical in the betel nut, and that the brain receptors turned on when they touched the saliva. "We've shown that if you just suck on the nut, there's a physiological reaction that can be released into your bloodstream and then into your brain, and that can alter human brain function," he says.
Then they sought to establish that these ancient people actually did it. In addition to matching the shape of betel nuts to the grooves in the teeth, they tested the dental tissues and found traces of arecoline — for which betel nuts are the only known natural source, Papke says.
Brumm also put himself in the mindset of ancient humans and tried sucking on betel nuts himself. "I had to give it a go," he says, "If you gently gnaw on the outside of it, it releases the betel juice. It has this extremely bitter and astringent taste that makes your whole mouth go numb."
He hypothesizes that the numbing, pain-relieving effect was what ancient hunter-gatherers were after. Brumm thinks the betel nut suckers eventually wore their teeth down to the nerve — which he says could have been very painful — leading to more nut-sucking to relieve the pain. "They were essentially caught in this cycle and they were basically addicted to this natural plant drug," Brumm says.
Human nature
Outside researchers say the paper makes a compelling case for ancient betel nut use. "There's evidence for the betel nut causing excessive tooth wear. When you add the chemical evidence, that's pretty much a smoking gun," says Peter Ungar, a distinguished professor of anthropology at the University of Arkansas who studies teeth and was not involved in this study.
"It fits with the bigger picture of our understanding of betel [nut] use and also the cultural dynamics of that time period," says Agustín Fuentes, professor of anthropology at Princeton University.
Others would like to see additional support for the theory. "I wish there was more, I must admit — there are two skeletons that they report," says Capriles at Penn State.
Capriles acknowledges that well-preserved ancient human remains are hard to find, especially in tropical areas where the heat and humidity breaks them down. Still, "more direct evidence would be the actual finding of the nuts, of the seeds, ideally in some form of cultural context," such as a hearth, house floor or burial site, he says.
And archaeologists not involved with the study are wary of making assumptions as to why ancient people were attracted to betel nuts. "We have to be very, very careful not to associate our particular assumptions of pain or patterns," says Fuentes, of Princeton. Regarding the researchers' theory that ancient peoples were addicted to betel nuts for their painkilling effects, "I think they're using a contemporary public health and dentistry approach to think about very complicated cultures of the past."
There might have been other social and cultural reasons for the teeth-damaging practice, Fuentes says. After all, people today eat hard candy, open bottles with their teeth, neglect to brush and floss. "All of these things are not directly good for your teeth, but they serve other social [purposes] in other kinds of contexts," he says.
Brumm, the lead researcher, acknowledges there are limitations to the work. "As always with archaeology, you're dealing with vast unknowns," he says, "But we've put a lot of thought into this, and we think this is what was going on."
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