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By Colin Barras

It must have been something in the air. During a short time window at the end of the last ice age, Stone Age humans in Europe and Asia independently began using a new plant: cannabis.That’s the conclusion of a review of cannabis archaeology, which also links an intensification of cannabis use in East Asia with the rise of transcontinental trade at the dawn of the Bronze Age, some 5000 years ago.Central Eurasia’s Yamnaya people – thought to be one of the three key tribes that founded European civilisation – dispersed eastwards at this time and are thought to have spread cannabis, and possibly its psychoactive use, throughout Eurasia.

The pollen, fruit and fibres of cannabis have been turning up in Eurasian archaeological digs for decades.Tengwen Long and Pavel Tarasov at the Free University of Berlin, Germany, and their colleagues have now compiled a database of this archaeological literature to identify trends and patterns in prehistoric cannabis use.It is often assumed that cannabis was first used, and possibly domesticated, somewhere in China or Central Asia, the researchers say – but their database points to an alternative.Some of the most recent studies included in the database suggest that the herb entered the archaeological record of Japan and Eastern Europe at almost exactly the same time, between about 11,500 and 10,200 years ago. “The cannabis plant seems to have been distributed widely from as early as 10,000 years ago, or even earlier,” says Long.

Weed as a cash crop

The researchers suggest that different groups of people across the Eurasian landmass independently began using the plant at this time – perhaps for its psychoactive properties or as a source of food or medicine, or even to make textiles from its fibres.However, Tarasov and Long’s database suggests it was only in western Eurasia that cannabis was then used regularly by humans down the millennia. Early records of its use in East Asia are fairly scattered, says Long.This pattern seems to have changed about 5000 years ago, at the start of the Bronze Age, when cannabis use in East Asia apparently intensified.Tarasov and Long think this timing is significant. By then, nomadic pastoralists on the Eurasian steppe had mastered horse riding, allowing them to cover vast distances and begin forging transcontinental trade networks following the same routes that would become the famous Silk Road several millennia later.This earlier “Bronze Road” allowed all sorts of commodities to spread between west and east, potentially including cannabis.“It’s a hypothesis that requires more evidence to test,” says Long, but he points out that the high value of cannabis would have made it an ideal exchangeable good at the time – a “cash crop before cash”. And independent lines of evidence suggest that commodities and people were on the move in the early Bronze Age. For instance, Long says that wheat, which was cultivated about 10,000 years ago in the Near East, first appeared in China 5000 years ago.Ancient DNA studies published in the last few years also confirm that one nomadic pastoral population of the steppe – the Yamnaya – began spreading both east and west at this time too.

Stoned age?

Rob Clarke at the International Hemp Association in Amsterdam, the Netherlands, who has written extensively on the prehistory of cannabis, welcomes the up-to-date work – and says it backs his conclusions that cannabis was domesticated in more than one place. The proposed link between the spread of cannabis and changes at the dawn of the Bronze Age does not surprise him.Because people can use cannabis in so many ways, we can’t be sure that its Bronze Age spread was linked specifically to its psychoactive properties, says Ernest Small at Agriculture and Agri-Food Canada in Ottawa.However, there are reasons to believe that its mind-bending properties were a factor. Some researchers have suggested that burned cannabis seeds found at archaeological sites hint that the Yamnaya carried the idea of smoking cannabis with them as they spread across Eurasia.David Anthony at Hartwick College in Oneonta, New York, who studies the Yamnaya, says the population may have used cannabis for its psychoactive properties on certain special occasions. “The expansion of cannabis use as a drug does seem to be linked to movements out of the steppe,” he says. “Cannabis might have been reserved for special feasts or rituals.”What’s more, Barney Warf at the University of Kansas in Lawrence says that we know from early Greek historians that post-Bronze Age nomadic pastoralists of the steppe who came after the Yamnaya – the Scythians – regularly used cannabis as a drug.“People talk about Herodotus’s accounts of hanging out in the Crimean peninsula smoking weed with the Scythians,” he says. Warf says the new work is fascinating, and should encourage more researchers to explore the history and prehistory of cannabis. “I think there’s a largely untold story of cannabis in Europe from the Bronze Age up until the Renaissance,” he says.

Journal reference: Vegetation History and Archaeobotany, DOI: 10.1007/s00334-016-0579-6