The present LRCUG review and recommendations are principally science-based and geared towards related audiences. differentiated and specifically tailored communication approaches will be required for different target audiences . These efforts may need to vary for different age, cultural or other specific groups and involve different communication styles and media formats. These ‘knowledge translation’ challenges are similar to those for other health interventions and need to be better understood and their effects evaluated .According to Small , the consequences of artificial selection make it impossible to determine if unaltered primeval or ancestral populations still exist. This author recommends that C. sativa be recognized as a single species with a narcotic subspecies and a non-narcotic subspecies , each with domesticated and ruderal varieties. A similar approach is the definition of four major biotypes of cultivated Cannabis with morphological and chemical differences submitted to different uses, either fiber/oil or drug production . There is also a hybrid between NLD and BLD, known as sinsemilla, which is highly psychoactive and, hence, is used mainly as a drug. The sinsemilla cultivars were developed in the New World and diffused worldwide. In contrast to the former biotypes, this hybrid is only cultivated, with no feral escapes or ruderal populations. The current distribution of these biotypes is shown in Fig. 1. Cannabis sativa is a sun-loving species that requires well-drained and nitrogen-rich soils, warmth and moisture. Therefore, most natural populations are found seasonally across accommodating northern temperate latitudes.
This plant grows well along exposed riverbanks, lakesides, margins of agricultural lands and other areas disturbed by humans. Cannabis plants are annual and usually diecious, as determined by X and Y chromosomes, and anemophylous . The annual cycle extends from spring to summer and autumn . Male plants, which are slightly taller than female plants, die shortly before pollination. Female plants ripen viable seeds just before the arrival of winter killing frosts. Seed dissemination is carried out mostly by wind or feeding birds. During germination, plant benches seeds are surrounded by bracts with hairs that produce a resinous blend of cannabinoids and aromatic compounds as secondary metabolites, which are believed to protect seeds against pests and pathogens.Almost all parts of the Cannabis plants are utilized for a variety of uses . For example, stem bark and fiber are used for cordage, woven textiles, building materials, paper, animal bedding and fuel. Seeds and seed oils are used for human food, animal feed, industrial feedstock and fuel. Female flowers and seeds are used for medicine or recreational drugs. All parts of the plant, primarily bark, seeds and female flowers, are used in ritual and social activities . Cannabis populations may also be used for environmentally related activities, such as the control of soil erosion and to increase CO2 sequestration. Esthetic and educational applications include botanical gardens and the iconic character of the plant as a symbol of a very ancient crop deeply rooted in human culture . Early attempts to identify the place of origin of wild Cannabis prior to human contact were based on the geographic distribution of its wild, cultivated and ruderal populations, combined with the known ecological requirements and reproductive strategies.
However, the distribution of this plant and its biotypes/varieties is closely associated with human settlements and trade routes, and therefore, the original native range is obscured . In spite of this, a broad area referred to as central Asia was proposed as the center of origin of Cannabis . Another, less generally accepted, possibility mentioned was south Asia . Regarding timing, accepting that the central Asian steppes were colonized by humans by 35,000 years ago , it has been assumed that wild Cannabis could have originated earlier. These hypotheses, however, were based on circumstantial evidence, and robust empirical evidence was lacking. This empirical evidence was provided by the fossil record and the use of time-calibrated molecular DNA phylogenies.The macrofossil record of Cannabis is relatively scarce and consists of only a few leaf and fruit/seed impressions with ages ranging between the Oligocene and the late Miocene . However, microfossils, specifically pollen, are abundant and widespread and have commonly been utilized to reliably reconstruct the history of Cannabis. Nevertheless, the identification of Cannabis pollen deserves special attention because of its similarity with other members of the family Cannabaceae, especially Humulus , a sister genus that bears contrasting ecological requirements and cultural connotations. Therefore, inaccurate identification might lead to erroneous conclusions . This is why different authors have used broader taxonomic categories for this pollen type, such as Cannabis-type, Cannabis/Humulus or Cannabaceae. In addition, it is unclear whether pollen from wild and cultivated Cannabis may be distinguished morphologically. Several morphological details have been suggested to be useful to differentiate Cannabis and Humulus pollen. Godwin emphasized several differential characteristics of the pore complex. Further statistical studies revealed that Cannabis pollen is generally larger than Humulus, but this character alone was not sufficient to allow reliable separation .
Pollen size also seems to be an unreliable parameter to separate wild from cultivated Cannabis . The combination of pore complexes and size seems to provide a more reliable, yet not universally accepted, identification criterion to differentiate between Cannabis and Humulus pollen . However, even in the case of conclusive Cannabis pollen identifications, comparisons with studies referring to this pollen type as Cannabistype, Cannabis/Humulus or Cannabaceae remain problematic, which may be a handicap for the development of meta-analyses aimed at reconstructing past biogeographic and cultural patterns. Recently, some meta-analyses have been conducted using different criteria, such as considering the entire Cannabis/Humulus complex or taking into accountonly those studies that explicitly identified Cannabis pollen . These approaches tend to overestimate or underestimate the actual pollen record of Cannabis. A different approach, called here the assemblage approach, has recently been proposed by McPartland et al. . These authors noted that wild C. sativa is typical of open temperate steppe habitats dominated by grasses, chenopods and Artemisia, whereas Humulus is a vine plant that requires trees to climb and is common in temperate deciduous forests dominated by alder , willow and poplar . A third assemblage corresponds to cultivated Cannabis, which is usually found together with cultivated cereals such as Avena , Hordeum , Secale and Triticum , as well weeds such as Centaurea or Scleranthus species. Using these phytosociological affinities, McPartland et al. attributed the Cannabis-like pollen types recorded in the literature to wild Cannabis if this pollen occurred together with steppe assemblages; to cultivated Cannabis when it was part of crop assemblages; or to Humulus if the dominant pollen assemblage corresponded to temperate deciduous forests. Based on these premises, these authors developed a more complicated identification algorithm that also considers the relationship between arboreal and non-arboreal pollen . Using these criteria, the oldest known pollen compatible with Cannabis was found in 19.6 Ma-old rocks from the NE Tibetan Plateau , which was proposed as the center of origin of Cannabis . Interestingly, this proposal roughly coincides with the former hypothesis based on indirect biogeographic evidence.
The use of DNA molecular phylogenies calibrated with fossils of related genera such as Humulus, Celtis, Morus and Ficus allowed to estimate the age of divergence of Cannabis and Humulus to 27.8 Ma . Using the same DNA phylogeny and the associated molecular clock, the divergence between C. indica and C. sativa would have occurred in the Middle Pleistocene approximately 1 Ma . These authors noted that there is a gap of ca. 8 million years between the age of origin estimated by the molecular clock and the first fossil pollen encountered. In spite of this, they favored the mid-Oligocene age for the origin of Cannabis on the NE Tibetan Plateau , assuming that, as demonstrated by the presence of Artemisia and other steppe elements, the region was covered by this type of vegetation, which would have been particularly well suited for the development of Cannabis. A previous study using Bayesian calibration estimated the divergence between Cannabis and Humulus to have occurred 21 Ma , which is closer to the age of the first fossil pollen evidence mentioned above . According to pollen and seed fossil records, Cannabis would have experienced some expansion from its center of origin to Europe and East Asia well before the evolutionary appearance of the genus Homo . The suggested dispersal agents are water and animals . The first expansions occurred to the west and the east during the Miocene-Pliocene. Most parts of the Asian continent were colonized by Cannabis during the Pleistocene , rolling bench before the onset of the Neolithic, when humans domesticated the first plants. During the Pleistocene, glacial-interglacial recurrence could have contributed to Cannabis diversification without human intervention. It has been suggested that Cannabis underwent recurrent range contractions and expansions that facilitated allopatric processes, possibly leading to the differentiation between the European and Asian subspecies, which would have diverged nearly 1 Ma .
The first is considered the putative hemp ancestor , and the second is the putative drug ancestor . In addition to fossils and DNA phylogenies, archeological evidence is of paramount importance to reconstruct domestication and anthropogenic diffusion trends within Cannabis. The main types of evidence of Cannabis from archeological sites are pollen, seeds, fibers, fiber/seed impressions, carbonized remains, phytoliths and chemical remains. During the historical period, written and graphic documents are also of fundamental help . Pollen identification has some additional clues related to its abundance in sediments, as Cannabis produces much more pollen than Humulus, which is usually underrepresented . This is especially useful in cases of very high percentages of this pollen type, which are difficult to explain unless the sediments come from a former hemp-retting site. Indeed, when flowering male hemp plants are soaked in a retting pond to separate the fibers from the stalk, large quantities of pollen settle into pond sediments. In these situations, the percentages of Cannabis pollen in sediments may reach 80–90% of the total, but percentages over 15% or 25% have been considered sufficient to infer hemp retting . The anemophylous pollen of Cannabis may be transported long distances; therefore, the finding of a few grains or their scattered occurrence throughout a stratigraphic section is not necessarily evidence for the local presence of the parent plant. Recent developments in molecular DNA analytical methods have increased the probability of identifying Cannabis sativa in lake sediments and comparing these results with the abundance of Cannabis/Humulus pollen. For example, in lake sediments from the French Alps, Giguet-Covex et al. found a good agreement between DNA and pollen records for the period 1500–1000 yr BP but significant inconsistencies for the periods 2000–1500 yr BP and 500 yr BP-present.
During these periods, the Cannabis/Humulus pollen attained values of 10–15% and DNA was undetectable, which could be attributed to the dominance of Humulus pollen in the pollen record. The debate regarding the Cannabis center of domestication has paralleled the taxonomic controversy on Cannabis species that, as seen before, was already active by the time of Linnaeus and Lamarck. See, for example, Clarke and Merlin and Small for more details on this long-standing discussion. Whether single or multiple centers of Cannabis domestication occurred has profound implications for the tempo and mode of Cannabis diffusion in Eurasia, where the plant evolved and was domesticated. Some authors have proposed that Cannabis was domesticated in Central Asia by 12,000 BCE , which would place Cannabis among the oldest human domesticates . A recent genome-wide phylogeographic study supports a unique center of domestication in east Asia , from which all biotypes would have emerged and dispersed throughout the world . According to this analysis, early domesticated ancestors of hemp and drug types diverged from wild Cannabis ca. 12,000 yr BP, which indicates that the species had already been domesticated by early Neolithic times. Among the defenders of the single center hypothesis, Small suggested that Cannabis was domesticated in the northern Caspian Sea and that the four different domesticated groups were transported to other parts of the world during the last millennium. These four groups coincide with the above mentioned biotypes NLH , BLH , NLD and BLD .