Cannabis: Evolution and Ethnobotany (University of California Press, 2016) by Robert Clarke and Mark Merlin is a comprehensive, interdisciplinary exploration of the natural origins and early evolution of this famous plant, highlighting its historic role in the development of human societies. This section comes from the chapter on “The Cultural Diffusion of Cannabis”.
Toward the end of the second millennium and into the twenty-first century, Cannabis production underwent significant changes that will continue to direct the evolution and dissemination of both hemp and marijuana varieties well into the foreseeable future. Prosecution for the cultivation of drug Cannabis in Western countries carried increasingly harsh penalties and clandestine growers moved their crops indoors under artificial growing conditions to avoid detection by law enforcement. At the same time, industrial hemp was given renewed legal status in many jurisdictions; consequently commercial fiber and seed cultivation spread across Europe, seed production began in Canada and New Zealand, and hemp field trials and breeding projects were initiated in many locations. Asian nations such as China also expanded hemp production to meet increased Western market demand. New industrial hemp fiber and seed varieties are being developed using interspecies hybrids between C. sativa ssp. sativa NLH and C. indica ssp. chinenesis BLH with the intention of expanding the range of industrial hemp production into more equatorial areas where present-day European NLH cultivars do not grow well. Medical Cannabis breeding targeted increased THC and other cannabinoid levels as well as unique terpenoid profiles. However, the United States, despite becoming the world’s largest importer of hemp fiber and seed products, still resists the legalization of industrial hemp growing. All these trends result from changes in the legality of Cannabis, either restrictive or supportive, in Western societies. This involved both the tightening of laws to curb illegal drug production as well as the acceptance of hemp as a viable industrial crop and the consequent amendment of national drug laws and international treaties to allow its cultivation.
North American and European BLD × NLD sinsemilla varieties are now commonly grown in most Western nations including Australia and New Zealand. Modern hybrids and alien landraces frequently reach rural agrarian cultures in developing nations where farmers once cultivated their own traditional fiber and drug landraces, and in recent years, hybrid seed produced in North America and Europe has been increasingly grown in traditional marijuana and hashish producing nations (e.g., Mexico, Morocco, Nepal, Jamaica, Colombia, and Thailand). Traditional outdoor growing, as well as indoor, artificial light cultivation of specially selected hybrid varieties, will continue to increase worldwide as the market for high quality marijuana and hashish expands. As exotic seed is increasingly disseminated to commercial growing regions, introduced varieties hybridize with established traditional varieties. Consequently the genetically pure local landraces are contaminated with introduced genes and become extinct. Although Cannabis as a whole flourishes around the world and is far from becoming extinct, we have lost much of the genetic diversity of the 1970s and 1980s, when landrace varieties were commonly grown by traditional agrarian cultures in isolated geographical habitats and new seed introductions to the West from foreign sources occurred frequently. In return, Western seed breeders (via marijuana growers and smugglers) introduced their “improved” hybrid varieties into traditional Cannabis-growing cultures and unwittingly aided in the extinction of their favorite landrace varieties.
Indoor, artificial light and glasshouse marijuana crops are now most commonly grown from vegetatively reproduced hybrid BLD × NLD cuttings, and seeds are rarely used except to grow replacement cutting stock. This limits crop improvement through selective breeding as seeds are rarely used or produced, and as a result, sexual reproduction stops, and evolution ceases or certainly slows down dramatically. However, sinsemilla breeders continue to develop early-maturing and high-yielding varieties that are short and compact for indoor grow room use and to avoid detection outdoors. Since the 1990s, indoor sinsemilla marijuana crops have been grown for purported medical use as state and local jurisdictions across North America and Europe increasingly recognize medical Cannabis as a separate issue from recreational use and legislate accordingly. The spread of vegetatively produced clones into artificial environments during Phase 6 increased Cannabis’s range into urban areas where water, electricity, agricultural inputs, and privacy are all readily available. This has finally brought at least some drug Cannabis varieties into full domestication and therefore complete dependence on humans for their survival and proliferation. It has also made illicit drug Cannabis production even more difficult to control.
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Excerpted from Cannabis: Evolution and Ethnobotany (2016) by Robert Clarke and Mark Merlin with permission of University of California Press.