Across the last twenty or so years numerous chemotaxonomic and genetic studies had attempted to understand cannabis origins, when and where cannabis acquired such different properties, and how the cannabis plant should best be classified.
Both cultivated and wild cannabis plants found throughout the world can look quite different: being either narrow leaf or broadleaf, more or less bushy, either shorter or taller, being more green, yellow, blue, red, or purple, and having different flowering periods. Furthermore, some varieties—generally known as hemp—have almost no psychoactive properties, while others are strongly psychoactive.
How Should Cannabis be Classified?
As discussed in a recent blog (Cannabis Sativa vs. Cannabis indica: What’s the Difference Today?), disagreement amongst botanists about how the various kinds of cannabis plant found throughout the world should be classified has been going on since the late 18th century.
The botanical classification of cannabis remains one of the most controversial among plant species. As does cannabis origins.
Is there, as some scientists suggest, only one ‘original’ cannabis variety, Cannabis sativa (or possibly Cannabis ruderalis)? Based on either chemical or genetic research, other scientists have alternatively argued that there were two ‘original’ varieties, Cannabis sativa and Cannabis indica. Others suggest three ‘original’ varieties, Cannabis sativa, indica, and ruderalis. Hillig (2004:881; 2005:176) proposes either two or three original varieties, diverging into seven subspecies of cannabis. Or, as recently argued by McPartland (McPartland et al. 2018; McPartland and Small 2020), should cannabis more accurately be classified as only Cannabis sativa, having four main subspecies: (1) South Asian domesticate; (2) South Asian wild-type; (3) Central Asian domesticate; (4) Central Asian wild-type?
It is now agreed by all researchers that the breeding of cannabis by humans, who began farming around 5,000 BCE, contributed to the variety of cannabis plants.
However, the main points of contention that remain are how these varieties should be classified and where the divergent varieties first grew.
A Recent Study to Define Cannabis Origins
A recently published study of cannabis genetics by Ren et al. (2021) agrees with the conclusions of some scientists while disagreeing with others. Ren et al. conducted a genetic analysis of 110 genomes of Cannabis sativa. The results were published on July 16th, 2021, in Science Advances.
From an analysis of the DNA sequences of the plants, the researchers formulated phylogenetic trees, which indicated four genetically distinct varieties of cannabis.
1. Basal Cannabis. This variety is proposed as the “sister” to all other cannabis varieties, including those with low psychoactivities, such as hemp varieties and psychoactive varieties.
2. Hemp Cannabis. Hemp cannabis, which has a low THC content, is known from several archaeological studies cultivated for fibre and cloth for around 7,000 years. However, the study by Ren et al. indicates that this date should now be pushed back further. They maintain that cannabis cultivation first occurred 12,000 years ago when a split between Basal Cannabis and Hemp Cannabis occurred. This would make cannabis one of the first cultivated crops in the world. They also propose that the split between Basal Cannabis and Hemp Cannabis, which occurred when cultivation began, happened in East Asia, in Western China.
This proposal shifts one of the centres of origin for cannabis slightly further east than Central Asia, which many scientists maintain is one of the original regions of the cannabis plant. The East Asian centre of origin of cannabis cultivation also fits with data that East Asia was historically a “hotspot” for the domestication of several crop species, including rice, broomcorn, foxtail millet, soybean, foxnut, apricot, and peach.
3. Wild Drug Cannabis. This variety of cannabis has a relatively high THC content. It is found in wild strains of cannabis growing in China, India, and Pakistan.
4. Cultivated Drug Cannabis. Cannabis has been cultivated for psychoactive properties for thousands of years, resulting in a distinctive genetic type.
One of the novel findings resulting from the research by Ren et al. is the identification of Basal Cannabis as a distinct category of cannabis. Another finding is that owing to selective breeding of cannabis for either fibre or resin, by around 4,000 years ago, cannabis crops formed distinctive hemp and drug cannabis groups. Before this time, cannabis was probably a multipurpose crop. As a result of selection for particular qualities, Ren et al. believe that the original, wild ancestors of Cannabis sativa may have become extinct.
Cannabis Origins: Conclusion
The history of the multi-faceted cannabis plant is highly complex. The recently published analysis of Ren et al. furthers our understanding of its historical human use and cultivation.
One issue that seems agreed on by all researchers who have conducted rigorous scientific chemotaxonomic or genetic studies is that a simple, binary distinction between psychoactive ‘marijuana’ and non-psychoactive ‘hemp’ is now no longer sustainable.
Future research will undoubtedly fill in the gaps in our knowledge of the history, chemistry, and cannabis origins to help better understand its future.
Hillig, Karl W. (2004). ‘A chemotaxonomic analysis of terpenoid variation in Cannabis. Biochemical Systematics and Ecology, vol. 32, pp. 875–891.
——— (2005). ‘Genetic evidence for speciation in Cannabis (Cannabaceae). Genetic Resources and Crop Evolution, vol. 52, pp. 161–180.
McPartland, John M., Geoffrey W. Guy, and William Hegman (2018). ‘Cannabis is indigenous to Europe and cultivation began during the Copper or Bronze Age: a probabilistic synthesis of fossil pollen studies.’ Vegetation History and Archaeobotany, vol. 27, pp. 635–648.
McPartland, John M., and Ernest Small (2020). ‘A classification of endangered high-THC cannabis (Cannabis sativa subsp. indica) domesticates and their wild relatives. PhytoKeys, vol. 140, pp. 81–112.
Ren, Guangpeng, Xu Zhang, Ying Li, Kate Rideout, Martha L. Serrano-Serrano, Yongzhi Yang, Ai Liu, Gudasalamani Ravikanth, Muhammad Ali Nawaz, Abdul Samad Mumtaz, Nicolas Salamin, and Luca Fumagalli (2021). ‘Large-scale whole-genome resequencing unravels the domestication history of Cannabis sativa.’ Science Advances, vol. 7, no. 29, eabg2286 (16th July).