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How humans brought cannabis to every corner of the globe

Cannabis is everywhere: today, the plant grows on every continent except Antarctica. But that wasn’t always the case. So how did this “weed” come to take over the world?

Its success is due in large part to us. The evidence suggests that cannabis first evolved nearly 28 million years ago on the Tibetan plateau, after splitting off from the last common ancestor it shared with the hop plant. At first, early humans may have unwittingly spread it. By clearing vegetation for settlements and heaping food scraps in waste dumps, they gave cannabis what it needed to thrive: open, sunny areas with fertile soil. That is why some scientists refer to the plant as a weedy “camp follower”.

In time, humans came to appreciate the many uses of the cannabis plant, and it is believed to be one of the first plants we cultivated when we began farming around 12,000 years ago. The stalks could be dried to create fibres, the seeds could be eaten or used to make oil and the resin-coated bracts could have been used for their medicinal and mind-altering purposes (though evidence for the latter is much more recent).

The plant’s utility enabled its spread and humans became the most important agent for its dispersal. Its seeds aren’t encased in tasty fruit, making them less attractive to animals, and they are round and heavy and lack wings that would let them hitch a ride on the wind.

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A million years of marijuana: How cannabis became our favourite weed

From the Tibetan plateau, the plant spread across central and East Asia, with nomadic groups later carrying it into the Indian subcontinent, eastern Europe and the Middle East by about 2000 BC. As people began to cultivate cannabis for a broader range of uses, including its psychoactive effects, different varieties of the plant emerged. This gave rise to the two major types we know today – Cannabis sativa and Cannabis indica – though there is still debate over whether these are actually separate species or just different types of the same species.

By the Middle Ages, cannabis was grown across Europe, and Arab and Indian traders carried it into Africa and South-East Asia. Finally, colonial empires brought the plant to the Americas beginning in the 16th century.

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