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

Abstract

Biogeographers assign the Cannabis centre of origin to “Central Asia”, mostly based on wild-type plant distribution data. We sought greater precision by adding new data: 155 fossil pollen studies (FPSs) in Asia. Many FPSs assign pollen of either 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, Robinia, Juglans) was identified as Humulus. C–H pollen curves that upsurged alongside crop pollen were identified as cultivated hemp. Subfossil seeds (fruits) at archaeological sites also served as evidence of cultivation. All sites were mapped using geographic information system software. The oldest C–H pollen consistent with Cannabis dated to 19.6 ago (Ma), in northwestern China. However, Cannabis and Humulus diverged 27.8 Ma, estimated by a 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 Cannabis centre of origin, in the general vicinity of Qinghai Lake. This co-localizes with the first steppe community that evolved in Asia. From there, Cannabis first dispersed west (Europe by 6 Ma) then east (eastern China by 1.2 Ma). Cannabis pollen in India appeared by 32.6 thousand years (ka) ago. The earliest archaeological evidence was found in Japan, 10,000 bce, followed by China.