Chemical analysis of several wooden pots, known as braziers, recently excavated from tombs in western China provides some of the earliest evidence for ritual cannabis smoking, researchers report. The study, published in the June 12 issue of Science Advances, suggests that smoking the plant for ritual activities was practiced in western China by at least 2,500 years ago.
"There has been a long history of attempting to push back the antiquity of cannabis use," said study co-author Robert Spengler, laboratory director at the Max Planck Institute for the Science of Human History in Jena, Germany. "[It] is one of the most contentious topics in the study of human cultural developments, and there have been many highly speculative conclusions drawn."
In some cases, earlier reports of cannabis use have been proven false, and in many cases, old studies need to be revisited, Spengler said. Previous evidence for cannabis used in religious contexts dates back as far as 2,800 years ago, in fact, but analyses of these remains do not adequately reveal how the cannabis plant was used.
"This study provides a solid point in time where we can say people were using it as a drug," said Spengler.
Psychoactive plants such as ephedra, poppy and cannabis can cause various altered states of consciousness and lead to unique spiritual and physical feelings and experiences. Despite being one of the most widely used psychoactive drugs in the world, however, evidence for the use of cannabis in the ancient world comes primarily from historical texts written by the Greek historian Herodotus, which scholars question. Archaeological findings relating to the use of cannabis as a drug are quite limited.
Recently, ten wooden braziers containing stones with obvious burning traces were exhumed from eight tombs at the Jirzankal Cemetery, located in a mountainous region in the northwest of China, which date to approximately 2,500 years ago.
"When we saw the braziers," Spengler said, "we had a hunch that they may have had a specific ritual function, such as for burning psychoactive plants or aromatics as part of the mortuary rituals."
To investigate, they extracted organic material from the wooden fragments and burnt stones and analyzed them using gas chromatography-mass spectrometry.
To the team's surprise, the results of their spectrometry analysis of the braziers showed an exact match to the chemical signature of cannabis with a high amount of cannabinol (CBN), the byproduct of tetrahydrocannabinol (THC), the most potent psychoactive agent in the plant.
With higher THC levels than typically found in wild plants at the time, the plants were probably used for their psychoactive properties, the authors say. Smoking was likely performed during burial ceremonies, perhaps as a way to communicate with the divine or the dead.
The findings corroborate other early evidence for cannabis from burials further east and north, in the Xinjiang region of China and in the Altai Mountains of Russia.
"It's beyond the scope of our study to answer if these people discovered a naturally higher THC-producing wild variety, or if they played [an active] role in changing the chemical compounds in the plant," said Spengler.
Not all plants are domesticated through a long process involving humans. Some have been domesticated in a "fast way," Spengler explained, simply by humans moving them great distances, for example along the Silk Road.
The findings of the study support the idea that cannabis plants were first used for their psychoactive compounds in the mountainous regions of eastern Central Asia, later spreading down the Silk Road and other routes to other regions in the world.
"The Silk Road shows the active interaction of multiple cultures and beliefs," said Spengler, "and the exchange of various plant resources along these trade routes has greatly enriched the material and spiritual life for peoples across Europe and Asia."
"Many of the most familiar plants in our kitchens today traveled for at least part of their long history along the Silk Road," he added.
Spengler said whether people were cultivating cannabis with higher THC 2,500 years ago or naturally stumbled on a more potent variety merits further study, "especially seeing that there is little to no evidence for drug cultivation in the ancient world."
The study further highlights the importance of residue analyses, which could open a unique window onto details of cultural communication in the past that other archaeological methods cannot offer.
"The field of residue analysis is expanding beyond the identification of diagnostic chemical compounds and branching into proteomics, lipids, and other metabolites," said Spengler. "There is an exciting and bright future for the archaeological sciences."
"In some cases," said study co-author Yimin Yang, a laboratory director at the University of Chinese Academy of Sciences in Beijing, "if small remains of animals and plants are not found [near artifacts], organic residue analysis could provide important information about animal or plant exploitation."
The discovery fits into a much larger understanding of the development of drug use by humans globally.
"People have always been attracted to plants that have specific chemical-based effects on the human body," said Spengler. "It should be no surprise that people two and a half millennia ago were able to understand and target the special metabolites of these plants. This study shows how innovative people are and how intimate the human relationship with plants has always been."