While this medicinal and psychotropic plant was long thought to have first evolved in central Asia, scientists were hazy on the precise location. That’s because there isn’t much evidence of ancient cannabis in fossil impressions — imprints that plants leave behind in rock.
A team of researchers led by the University of Vermont in the US examined 155 existing fossil pollen studies from Asia in order to ‘to reconstruct the evolutionary and human related history of Cannabis in Asia’, said the authors in the report.
For the new study, researchers separated Cannabis and Humulus pollen from 155 studies and mapped them to regions across Asia, to clarify where and when Cannabis emerged. [25 Odd Facts About Marijuana]
The scientists identified fossil pollen as belonging to Cannabis plants if it appeared alongside other types of pollen from a steppe ecosystem — open, treeless habitats where Cannabis is known to thrive. They discovered that the earliest Cannabis fossil pollen placed the genus in northwestern China, and dated to about 19.6 million years ago.
But Cannabis diverged from Humulus around 28 million years ago, suggesting that it might have originated somewhere else, the study authors wrote in the new study.
While the researchers didn’t find any Cannabis pollen dating to 28 million years ago, they did find 28-million-year-old pollen from Artemisia, another genus of steppe plant that grew abundantly alongside Cannabis millions of years later. This earliest evidence of Artemisia showed up on the Tibetan Plateau near Qinghai Lake, a location about 10,700 feet (3,260 meters) above sea level.
Using a statistical model, the study authors estimated that since the assembly of plants in that location — including Artemisia — were found with Cannabis in other locations millions of years later, it was likely that Cannabis was also present in this high-altitude ecosystem, even if there was no direct evidence of Cannabis pollen, they wrote in the study.
From the Tibetan Plateau, Cannabis reached Europe approximately 6 million years ago, and spread as far as eastern China by 1.2 million years ago, the scientists reported.
One reason the origins of the plant have been so hard to trace is because the leaves of cannabis plants – such as hemp – don’t create very good print fossils, and only two collections of the plant fossil exist.
In contrast, hundreds of pollen fossils have been found and analysed, which the current study reviewed.
While widely known as a drug, the cannabis plant in fact had may functions for communities that used its plant fibres, for providing cordage and textiles, for example.
Carbonised hemp fibres, found with silk and spinning wheels, date to 5,600 BC, in Henan Province, China.
Researchers analysed studies of pollen fossils from the plant and showed that it disseminated over the millennia to Europe, China and then India.
It has long been known the plant originated in Central Asia but its exact location on the Tibetan plateau around Qinghai Lake (shown on map) had remained a mystery
Scientists also put down the appearance of cannabis elsewhere in the world down to tectonic movements of the earth, rather than humans migrating with it.
The researchers wrote: ‘Early floristic exchanges between India and Asia were shaped by plate tectonics,’ the researchers wrote in their paper.
‘As the Indian plate migrated towards the Asian plate, it made a ‘glancing contact’ with Sumatra 57 [million years ago], followed by Burma, and then a ‘hard collision’ with Tibet 35 [million years ago].
‘The glancing contact between continents resulted in floristic exchanges during the Eocene.’
‘Cannabis holds significance in human history and life today as a triple-use crop. First, its fruits (seeds) provide valuable protein and essential fatty acids’, wrote the researchers.
Archaeological evidence in a food context dates back to 10,000 BC in Japan.
WHERE IS THE TIBETAN PLATEAU?
Also called Tibetan Highlands or Qinghai-Tibet Plateau, it is a vast high plateau of southwestern China.
It encompasses all of the Tibet Autonomous Region and much of Qinghai province and extends into western Sichuan province and southern Uygur Autonomous Region of Xinjiang.
It has an area of about 965,000 square miles (2,500,000 square km), is a region of tangled mountains and uplands that are generally above 13,000 to 15,000 feet (4,000 to 5,000 metres) in elevation.
Lhasa, the capital of Tibet, is the plateau’s major centre of population, economic activity, culture, and air and land transportation.
The findings were published online May 14 in the journal Vegetation History and Archaeobotany.