By sequencing genetic samples from the plant, they found that the species was most likely domesticated in the early Neolithic. They said their conclusion is supported by pottery and other archaeological evidence from the same period discovered in what is now China, Japan, and Taiwan.
But Professor Purugganan said he was skeptical of the conclusions that the plant was developed for drug or fiber consumption 12,000 years ago, as archaeological evidence shows that cannabis was consistently used or present for these purposes around 7,500 years ago.
“I would like a much larger study with a larger sample,” he said.
Luca Fumagalli, author of the study and a biologist in Switzerland who specializes in conservation genetics, said the theory of Central Asian origin is largely based on observational data from wild samples in that region.
“It is easy to find wild samples, but they are not wild types,” said Dr. Fumagalli. “These are plants that have escaped captivity and adapted to the wild environment.”
“That’s why you call it grass, by the way, because it grows all over the place,” he added.
The study was led by Ren Guangpeng, a botanist at Lanzhou University in western China’s Gansu Province. Dr. Ren said in an interview that the original location of cannabis domestication was most likely in northwest China and that the discovery could help in the country’s current efforts to breed new strains of hemp.
To conduct the study, Dr. Ren and colleagues 82 samples, either seeds or leaves, from around the world. Samples included strains selected for fiber production and others from Europe and North America bred to produce high levels of tetrahydrocannabinol (THC), the plant’s most mood-altering compound.
Dr. Fumagalli and his colleagues then extracted genomic DNA from the samples and sequenced them in a laboratory in Switzerland. They also downloaded and re-analyzed sequencing data from 28 other samples. The results showed that the wild varieties they analyzed were indeed “historical escapes from domesticated forms” and that existing varieties in China – cultivated and wild – were their closest offspring of the ancestral gene pool.