Updated: Oct 9
A July 2021 peer-reviewed research study entitled "Large-scale Whole-genome Resequencing Unravels the Domestication History of Cannabis Sativa" that was published in the journal Science Advances investigated the global domestication patterns of this controversial plant species, with a focus on its genetic evolution and possible ways to categorize the variability present in modern cannabis and hemp.
The study's authors noted that "despite its ancient use dating back thousands of years, the genomic [genetic] history of domestication of cannabis has been understudied compared to other important crop species" and that this was due to the legal status and restrictions placed on the plant.
"Few crops have been under the spotlight of controversy as much as cannabis," noted the research, which stated that marijuana was one of the first plants to be domesticated by humans. The study reported that cannabis features a "long and fluctuating history interwoven with the economic, social, and cultural development of human societies."
"Few crops have been under the spotlight of controversy as much as cannabis," noted the research, which stated that it was one of the "first domesticated plants."
It explained that the hemp version of the plant (containing only trace amounts of the psychoactive cannabinoid delta-9 tetrahydrocannabinol, or THC) was once "a major source for textiles, food, and oilseed" and that "its exploitation to that end declined in the 20th century" while its use as a lifestyle (recreational or adult-use) drug has increased.
How Many Species?
The scientists addressed the controversy of how many species compose the cannabis plant. Some have contended that cannabis is a single species, while others have suggested that it is two or even three species. "Although much debated in the past, it is currently widely accepted that the genus Cannabis comprises a single species, C. sativa L., hereafter also referred to as cannabis," reported the study.
The research noted that previous estimates about the geographical origins of cannabis, as a plant cultivated by humans, suggested a wide region ranging from "West Asia through Central Asia to North China," but that its data indicates that these estimates are not accurate. Regardless of its region of origination (revealed later in this homework assignment), the herb spread worldwide "with continuous artificial selection and extensive hybridization between locally adapted traditional landraces and modern commercial cultivars."
The study reported that explanation and "reconstruction" of the domestication history of cannabis has been difficult due to "clandestine drug breeding and the propensity of domestic plants to become feral."
The study reported that explanation of the domestication history of cannabis has been difficult due to "clandestine [underground]...breeding and the propensity of domestic plants to become feral."
The researches observed a "renewed global interest in the therapeutic potential of cannabis" and that this shift centers around the plant's unique chemical components (primarily cannabinoids, terpenes, and flavonoids, although many other types are present).
The study observed that "cannabidiolic acid (CBDA) and tetrahydrocannabinolic acid (THCA)" are the "two most abundant and studied of at least 100 unique secondary metabolites known as cannabinoids."
"The study noted that a chemical process called decarboxylation involves conversion of CBDA and THCA to the popular CBD and THC."
It noted that a chemical process called decarboxylation involves conversion of CBDA and THCA (particular types of cannabinoids called acidic precursors) to the popular cannabidiol (CBD) and THC, which it labeled as their "bioactive forms" (scientists sometimes refer to CBD and THC as the "neutral" versions of these cannabinoids).
The research explained that cannabinoids such as CBD and THC, when consumed by humans or any mammal, "bind to endocannabinoid receptors in an animal's central nervous system, eliciting a broad range of effects, some of which may alleviate symptoms of neurological disorders."
Hemp vs Cannabis
The researchers noted how the two modern forms of the plant, hemp and cannabis, differ. "Hemp cultivated for fiber typically produces higher concentrations of CBDA than THCA, whereas marijuana contains very high amounts of THCA and much higher overall levels of cannabinoids," reported the scientists.
"Hemp cultivated for fiber typically produces higher concentrations of CBDA than THCA, whereas marijuana contains very high amounts of THCA and much higher overall levels of cannabinoids."
They explained how hybrid cultivars "with high CBDA content are currently developed for medical use." The researchers also noted that the difference between hemp and cannabis is based mostly on "separate statutory definitions" and that, to be categorized as hemp, a plant must produce under 0.3 percent delta-9 THC in dry weight by volume (a standard observed in North America and the European Union).
Lack of Understanding
The study's authors lamented that "despite an increasing need to produce varieties with specific cannabinoid profiles for therapeutic and recreational exploitation...the mechanisms mediating the evolution of these genes are still not clearly known."
They reported that recent similar studies that analyze the DNA of modern cannabis cultivars and chemotypes that are "mostly Western commercial cultivars" revealed a significant genetic difference between hemp and cannabis.
"Given the large gaps in our knowledge of the evolutionary history of domestication of cannabis, a comprehensive reconstruction of [these] events...requires large-scale comparison of genomic data covering the full end use and geographic range," noted the research.
"Recent analysis of modern cannabis DNA has revealed a significant genetic difference between hemp and cannabis."
The study claimed that its investigation of this topic was "an unprecedented global sampling effort" and that it compiled "110 whole genomes covering the full spectrum of wild-growing feral plants, landraces, historical cultivars, and modern hybrids from both hemp and [cannabis]" and that it focused on central and eastern Asia "because of their hypothesized importance for the species' origins of domestication."
After collecting their data, the scientists classified the genetics of modern cannabis plants into four groups:
Group A—Basal Cannabis: Includes 14 feral plants and landraces collected in China and two feral plants from the United States (originating from 19th-century Chinese landraces).
Group B—Hemp: Includes hemp varieties distributed worldwide: Five feral plants, 13 landraces, and 20 cultivars.
Group C—Drug-type Feral: Includes three feral samples collected in Southern China, 11 feral plants collected in India and Pakistan (south of the Himalayas), and one drug cultivar from India.
Group D—Drug-type: Includes cultivated drug varieties distributed worldwide (35 cultivars total).
The study revealed "substantial differentiation between drug-type feral plants and one cultivar from an area covering both sides of the Himalayan range (Group C) and modern European and American marijuana cultivars (Group D) that have arisen via recent intense selection for THC-rich content."
Origin Stories & Extinction
Contrary to the "widely accepted view which associates cannabis with a Central Asian center of crop domestication," the study reported that its results "are consistent with a single domestication origin of C. sativa in East Asia, in line with early archaeological evidence."
It noted that its data and analysis "indicate that some of the current Chinese landraces and feral plants represent the closest descendants of the ancestral gene pool from which hemp and marijuana landraces and cultivars have since derived."
Of significance, the study reported that wild feral plants from Central Asia "nested within the Hemp-type Group B indicate that all feral plants studied here are not wild types, but historical escapes from domesticated forms."
The study's broad sampling results "suggest that pure wild progenitors of C. sativa have gone extinct."
Importantly, the researchers noted that more sampling of feral plants "in these key geographical areas is still needed," but that its broad sampling "suggests that pure wild progenitors of C. sativa have gone extinct."
The study found that "early domesticated ancestors of hemp and drug types diverged from Basal cannabis [Group A above] approximately 12,000 years ago, "indicating that the species had already been domesticated by early neolithic times" and that this coincides with the dating of "cord-impressed pottery from South China and Taiwan" and 10,000-year-old seeds from Japan.
The study found that "early domesticated ancestors of hemp and drug types diverged from Basal cannabis [Group A above] approximately 12,000 years ago, "indicating that the species had already been domesticated by early neolithic times*."
*Merriam-Webster defines neolithic as "of or relating to the latest period of the Stone Age characterized by polished stone implements." Also known as the New Stone Age, the Neolithic period included many important developments for humans, including the introduction of farming, the domestication of animals, and a shift from a hunter-gatherer society to one involving settlements.
The neolithic period began about 12,000 years ago and lasted until about 6,500 years ago (4500 BC), when the Copper Age dawned and humans learned metallurgy. The Copper Age was followed by the Bronze Age and the Iron Age.
The study also revealed that archeological sites featuring hemp-type cannabis artifacts "are consistently found from 7,500 years [ago] in China and Japan" and that cannabis pollen from cultivation efforts was found in China "more than 5,000 years ago." More recently, about 4,000 years ago, was a period during which "multiple fiber artifacts appeared in East Asia" and "fiber-grown cannabis" spread westward into Europe and the Middle East during the Bronze Age.
Archaeological evidence from about 2,500 years ago in Western China indicates that cannabis was involved in "ritualistic and inebriant use." The first "archaeobotanical record" of cannabis domestication in the Indian subcontinent "dates back 3,000 years" and the plant species likely was introduced from China with other crops.
The study revealed that archeological sites featuring hemp-type cannabis artifacts "are consistently found from 7,500 years [ago] in China and Japan."
"Historical texts from India from as early as 2,000 years [ago] indicate that the species was only exploited for drug use," reported the study. It explained that over the course of the following several centuries, recreational cannabis ("drug-type") spread to a number of world regions, including Africa in the 13th century, Latin America in the 16th century, and North America at the beginning of the 20th century. This included an influx of cannabis genetics into North America from the Indian subcontinent in the 1970s.
In contrast to the development of global availability of drug-type cannabis, "hemp-type cultivars were first brought to the New World by early European colonists during the 17th century." The study explained that these varieties were replaced in North America by Chinese hemp landraces by the mid-1800s.
The study's authors proposed that early domesticated cannabis was first used as a primarily multipurpose crop about 4,000 years ago, when it underwent "strong divergent selection for [either] increased fiber or drug production."
Domestication of cannabis lead to two primary types: "Tall hemp plants maximizing cellulose-rich/lignin-poor bast fibers in the stems" and "short marijuana plants with lignin-rich woody cores" that maximize flower and resin production.
They explained how domestication of cannabis lead to two primary types, including "tall hemp plants maximizing cellulose-rich/lignin-poor bast fibers in the stems" and "short marijuana plants with lignin-rich woody cores" that maximize flower and resin* production.
*The resin glands, called trichomes, appear on mature female plants and are the source of all cannabinoids and terpenes made by cannabis and hemp.
This detailed study summarized that its analysis "identified the time and origin of domestication, post-domestication divergence patterns and present-day genetic diversity, and genomic structure of an exhaustive worldwide panel of cannabis wild-growing feral, landrace, and cultivar representatives."
The scientists claimed that their study provides novel insight into the domestication and spread around the world of cannabis, a plant species "with divergent structural and biochemical products—at a time in which there is a resurgence of interest in its use." They noted evolving social attitudes and "corresponding challenges to its legal status in many countries."
"The scientists claimed that their study provides novel insight into the domestication and spread around the world of the cannabis plant species."
The study concluded that its data "provide support for an evolutionary scenario that accounts for the variability in cannabinoid composition among plants as a result of artificial selection by early farmers." It noted that its results "offer an unprecedented base of genomic resources for ongoing molecular breeding and...research" in both medicine and agriculture.
View the original study.