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.