Cannabis in Asia: its center of origin and early cultivation, based on a synthesis of subfossil pollen and archaeobotanical studies

Biogeographers assign the center of origin of Cannabis to Central Asia, mostly based on wildtype plant distribution data. We sought greater precision by adding new data: 155 fossil pollen studies (FPSs) in Asia. Many FPSs assign pollen of Cannabis or Humulus (C-H) to collective names (e.g., Cannabis/Humulus or Cannabaceae). To dissect these aggregate data, we used ecological proxies. C-H pollen in a steppe assemblage (with Poaceae, Artemisia, Chenopodiaceae) was identified as wild-type Cannabis. C-H pollen in a forest assemblage (Alnus, Salix, Quercus, Betula, Robinia, Juglans) was identified as Humulus. C-H pollen curves that upsurged alongside crop pollen were identified as cultivated hemp. Subfossil seeds (achenes) at archaeological sites also served as evidence of cultivation. FPSs and archaeological sites were mapped using geographic information system (GIS) software. The oldest C-H pollen consistent with C. sativa dated to 19.6 million years ago (mya), in northwestern China. However, Cannabis and Humulus diverged 27.8 mya, based on molecular clock analysis. We bridged the temporal gap between the divergence date and the oldest pollen by mapping the earliest appearance of Artemisia. These data converge on the northeastern Tibetan Plateau, which we deduce as the C. sativa center of origin. This co-localizes with the first steppe community that evolved in Asia. From there, Cannabis first dispersed west (Europe by 6 mya) then east (eastern China by 1.2 mya). Cannabis pollen in South Asia appeared by 32.6 kya. The earliest Cannabis seeds were found in Japan, 10,000 BCE, followed by China