A study published in a journal called Science Advances sheds some light on the origins of marijuana as we know it today. It turns out to be one of the very first plants that humans domesticated. 

Where is Weed From?

Marijuana is referred to as “weed” because it truly is a weed – it’ll grow anywhere. But scientists are trying to learn more about its origins and where it first flowered, not just where it’s spread from there.  The new study kicks out the theory that many botanists have held for quite some time, assuming the plant was first domesticated in Central Asia. That theory is based largely on data obtained from observational samples of wild cannabis plants within Central Asia.

The problem there is that those studies used feral samples that escaped captivity and readapted to the wild environment, not those that were wild to begin with.  The new research article is called “Large-scale whole-genome resequencing unravels the domestication history of Cannabis sativa” and it combines science and history to create a picture of how the plant has been used throughout millennia. The same plant we know today, the paper says, links back to early Neolithic times in East Asia.

The whole-genome resequencing study suggests the plant was first domesticated in Northwestern China and spread out from there.  “Our results provide support for an evolutionary scenario that accounts for the variability in cannabinoid composition among plants as a result from artificial selection by early farmers for loss-of-function mutations,” the researchers said. “Our results also offer an unprecedented base of genomic resources for ongoing molecular breeding and functional research, both in medicine and in agriculture.”

Domestication

The study contradicts another widely-held belief that during the Early Neolithic Era, plants were domesticated solely for their use as food. Researchers on this project found people in the New Stone Age were more likely to develop cannabis for fiber and for its psychoactive properties. The researchers saw distinct branches where the plant took on separate changes depending on who was breeding it: some wanted the heavy fiber content; others were after the THC.

Thousands of years ago, cannabis plants weren’t quite the same as they are now, researchers have found. There were two main cannabinoids competing with each other, affecting whether fiber production or psychoactive properties would increase in the plant.  The researchers compared the genes in fiber-heavy plants to those in THC-heavy plants and found they developed quite differently throughout time. The results suggest the plant was purposely being bred for drug use early on, with ancient plants showing progressively heavier cannabinoid content with “unbranched, tall hemp plants” for cellulose-rich fibers in the stems, compared with “well-branched, short marijuana plants” with woody cores that would produce the highest content of flower and resin. 

The researchers say archaeological and archaeobotanical evidence supports their findings.  “Our genomic dating suggests that early domesticated ancestors of hemp and drug types diverged from Basal cannabis ~12,000 years B.P. (95% confidence interval: 6458 to 15,728 years B.P.; Fig. 2B and table S3), indicating that the species had already been domesticated by early Neolithic times. This coincides with the dating of cord-impressed pottery from South China and Taiwan (12,000 years B.P.), as well as pottery-associated seeds from Japan (10,000 years B.P.).

Archaeological sites with hemp-type Cannabis artifacts are consistently found from 7500 years B.P. in China and Japan, and pollen consistent with cultivated Cannabis was found in China more than 5000 years B.P.” The researchers say there’s evidence of hemp-type cannabis artifacts as early as 7500 BP in both China and Japan. Scientists have also found pollen they believe comes from purposely cultivated cannabis in China more than 7000 years ago. That seems at first to have been their primary focus, with the fibrous strands being used for the production of goods.

The drug-type cannabis strains only appeared (in small numbers) around 4000 BP in China. At that time, the fiber-heavy cannabis was spreading to Europe and the Middle East.  Other countries seem to have used the plant differently from the moment they saw it. For instance, in India, historical texts show the species was used entirely for drug use from as early as 2000 years BP. The type of THC-heavy cannabis bred for recreational purposes was found in Africa in the 13th century, Latin America in the 16th century, and reached North America in the early 20th century.

Domestication of hemp proved hugely fruitful, with the plant being used for textiles, food, oilseed and more. But in the 1900s, people in North America really started to take a heftier interest in its recreational use. That’s partially because the need for textiles, food, and oilseed became less prevalent as we moved into the modern era. 

What the study entailed

The researchers’ pool included 82 cannabis samples from around the world. Those could be either seeds or leaves, and they included strains that had been specially-bred for fiber production, as well as those from Europe and North America that have been tailored to include larger amounts of THC. The scientists sequenced the genomic DNA from the samples, comparing them with reanalyzed sequencing data from another set of 28 separate samples. That’s how the scientists came to realize that the DNA sequence of the wild varieties they were looking at most closely resembled existing strains of both cultivated and wild marijuana plants in China.  

Setbacks in research

If the plant has been around for so long, why has it taken humans so long to realize that is has, in fact, been part of our very own history for such a huge chunk of time? The answer to the lack of historical research surrounding cannabis is the same as it is for the lack of medical research: because it remains a banned substance at the federal level, research involving the product is slim and difficult to achieve.  “Despite its ancient use dating back thousands of years, the genomic history of the domestication of Cannabis has been understudied compared to other important crop species, largely due to legal restrictions,” the researchers explain.