On the trail of hemp: the infamous herb is one of the oldest cultivated plants of humans, a study shows. Cannabis sativa was already grown around 12,000 years ago in today’s China, according to analyzes of the genomes of various wild and cultivated forms. According to the genetic traces, it was only later that the plants were cultivated more specifically for the production of fibers or active substances.
It can supply textiles, oils, but also intoxicating or medically effective substances to humans: Due to this complex meaning, Cannabis sativa has a very special cultural history that has been heavily influenced by controversy, especially since the 20th and 21st centuries. Because during this time it developed from a raw material supplier to a source of intoxicants in the form of marijuana or hashish. As is well known, their approval as legal luxury food is controversial in many countries. In recent decades, however, cannabis has increasingly come into the focus of medical research, because its various chemical components have therapeutic potential.
Searching for clues in genomes
But how did humans originally come across this unusual crop? From archaeological evidence it was already fundamentally known that hemp cultivation is thousands of years old and probably began somewhere in Asia. But where exactly people first specifically cultivated Cannabis sativa and the exact timeframe of domestication have so far remained unclear. Scientists working with Guangpeng Ren from the University of Lausanne have now investigated this question by looking into the genetic makeup of the plants. As part of their study, they analyzed a total of 110 genomes, which together cover the entire spectrum of known wild forms and cultivated varieties of Cannabis sativa.
As they explain, by comparing the genetic make-up they were able to uncover relationships and, based on certain genetic characteristics, draw conclusions about which versions are original and when the different groups were split up. Their results show that all of today’s hemp varieties – whatever their cultivation goal – can be traced back to common ancestors that were already cultivated in China in the Stone Age. The results specifically indicate that today’s varieties as well as overgrown cannabis plants in this region are closest to the original form. However, the pure wild form of Cannabis sativa is probably extinct, the researchers write.
Roots in the stone age
Their analyzes show a time window for domestication from 6500 to 15,000 years ago. Specifically, the time around 12,000 years ago appears particularly plausible. Because archaeological evidence previously suggested the use of hemp ropes in this era, the researchers report. “Contrary to popular belief that cannabis domestication occurred in Central Asia, our results point to East Asia – in accordance with archaeological evidence,” the researchers write.
As they further report, the results suggest “that the early domesticated cannabis was first used as a multi-purpose plant until about 4000 years ago, before it was subjected to a targeted breeding for increased fiber or drug production”. In this context, Ren and his colleagues identified several genes that were apparently selected for during cultivation. These include hereditary factors that are related to the branching and cellulose formation in the fiber hemp varieties, as well as a gene that is involved in the biosynthesis of the cannabinoids in the versions that are used for the production of medicinal or intoxicating substances. “Our results thus also offer fundamental genomic resources for hemp breeding and functional research – both in terms of medical and agricultural significance,” the scientists conclude.