Cannabis Domestication, Breeding History, Present-day Genetic Diversity, and Future Prospects

Humans and the Cannabis plant share an intimate history spanning millennia. Humans spread Cannabis from its Eurasian homelands throughout much of the world, and, in concert with local climatic and human cultural parameters, created traditional landrace varieties (cultivars resulting from a combination of natural and farmer selection) with few apparent signs of domestication. Cannabis breeders combined populations from widely divergent geographical regions and gene pools to develop economically valuable fiber, seed, and drug cultivars, and several approaches were used with varying results. The widespread use of single plant selections in cultivar breeding, inbreeding, and the adoption of asexual reproduction for commercial drug production, reduced genetic diversity and made many present-day cultivars susceptible to pathogens and pests. The great majority of drug Cannabis cultivars are now completely domesticated, and thus are entirely dependent on humans for their survival. Future ramifications remain to be realized.