High in the Pamir Mountains of western China, scientists exploring an ancient cemetery have uncovered 2,500-year old vessels containing the chemical remains of burned cannabis plants.
The discovery, described Wednesday in the journal Science Advances, marks the earliest solid chemical evidence that ancient people sought out cannabis for its mind-altering properties, and could shed light on the interactions between ancient human cultures as well as our evolving relationship with certain plants.
“What this shows is a close relationship between prehistoric populations and their wild botany,” said Michael Frachetti, an archaeologist at Washington University in St. Louis who was not involved in the work.
Humans have long had a complex relationship with cannabis, in part because cannabis is not just one plant with one set of properties. Strains of Cannabis sativa have been used for millennia to produce rope and textiles from the stalks and oil from the seeds.
And because wild cannabis typically has very low levels of tetrahydrocannabinol, the plant’s powerful psychoactive compound better known as THC, it’s unclear exactly when and how humans might have started inhaling smoke or ingesting plant matter for mind-altering purposes.
References to drug use, though unverifiable, abound in the historical record. The Greek historian Herodotus, who lived in the fifth century BCE, wrote briefly of the Scythians producing smoke from hemp seeds. The Rig Veda, an ancient Hindu religious text, refers to a mind-altering substance called “soma,” though it’s unclear exactly what it was made of.
But finding evidence of ancient people getting high is particularly difficult because such plant matter tends to degrade quickly. Earlier “discoveries” made at other archaeological sites were discredited later.
The artifacts from the site in western China, known as the Jirzankal cemetery, changes that. Situated some 3,000 meters above sea level, the funereal grounds are filled with tombs consisting of shaft chambers, most of which are covered with circular piles of stones.
The cemetery sits along what would come to be known as the Silk Road, a major network of trading routes that connected the Far East to the Middle East and Europe. Among the finds were glass beads and angular harps — typical of western Asia — and silk that likely would have come from eastern China, a clear sign of cultural exchange.
There were high rates of human exchange, too: Strontium isotope analysis of remains at the site shows that 10 out of 34 of interred individuals were not local to the community.
For this new study, researchers led by archaeologists Yimin Yang and Meng Ren of the University of Chinese Academy of Sciences examined 10 wooden braziers pulled from eight of the tombs. Within the braziers lay clearly burned stones.
The scientists took 20-milligram samples of the interior and exterior surfaces of nine containers, ground them into powder and subjected them to gas chromatography and mass spectrometry. They studied the residues on four of the stones as well.
When researchers tested the interior of the braziers, they found high levels of cannabinol, a metabolite of THC. Though the predicted THC levels would have been much lower than those in strains of cannabis cultivated today, they were still significantly higher than the levels found in typical wild cannabis plants.
Beyond the THC levels, the braziers themselves supplied the smoking gun, Frachetti said.
“It’s the difference between finding the residue of burnt cannabis versus finding an actual bong,” Frachetti said. “That’s going to be the indication that these things are being deployed as smoke, and that’s what these braziers really are. They’re showing a whole technology of releasing cannabis smoke.”
Yang made some guesses as to the cannabis smoke’s purpose. Perhaps it was used during funeral rites to communicate with nature, the divine or the deceased, the scientists said.
Intriguingly, only one of the 10 immigrants had been buried with a brazier — an indication that this practice might have been specific to the local community.
Such cannabis-based traditions may have varied widely across different cultures in Eurasia, Yang added.
It seems that human travelers did not just exchange cultures and communities along the Silk Road, they also shared plants and their knowledge of them. Cannabis was already widely used by communities along this route because it was so useful and so commonplace in central Asia.
But what made humans notice this plant’s potentially psychoactive properties, and when did they start prizing — and perhaps cultivating — these plants for their mind-altering powers?
Perhaps the exposure to high ultraviolet levels at those high altitudes triggered more THC production in wild plants, the researchers said. Or maybe the inhabitants had actively domesticated strains of this crop for its mind-altering chemical levels.
It’s “kind of an open debate that I think our study really puts out there but doesn’t actually have a good answer for,” said study co-author Robert Spengler, an archaeobotanist at the Max Planck Institute for the Science of Human History in Jena, Germany.
Frachetti said he suspected ancient people were burning cannabis to get high even before these tombs were dug.
“Do I think it was happening earlier? Yeah I do,” he speculated. “But this is interesting because it really puts a nail down to say, ‘OK, this is at least a date that we can say, by this time they’re deploying cannabis as smoke.’ ”
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