researchers have been able to trace all cannabis strains to a small number of original cannabis plants known as landrace strains, which are isolated plants that have not been crossbred with other cannabis varieties. they are indigenous to specific regions, and developed their particular qualities as the strain adapted to their unique environment.
paleobotanists used a method called “molecular clock,” to estimate when cannabis and its sister species humulus (hops) diverged from a common ancestor. the molecular clock uses dna to measure time, and calibrates the clock with fossil dates of related plants. using this method, they estimated that cannabis first diverged from a common ancestor 27.8 million years ago!
by researching a region in asia with fossilized pollen and measuring it with radiocarbon dating and tracking a plant called artemisia, which has a close alliance and parallel evolutionary pattern to cannabis, paleobotanists pinpointed the northeastern tibetan plateau as the cannabis center of origin. the tibetan plateau created an environment that supports the theory that cannabinoids developed to protect the plant from uv rays and herbivores.
fossil pollen records also tell us that cannabis dispersed into europe 6 million years ago and then later east into china 1.2 million years ago. by mapping the distribution of pollen over time, scientists were able to see that european cannabis went through repeated reductions in their populations. following the warm and wet holocene period, forests replaced open grasslands. cannabis retreated to the small pockets of open space that it could inhabit, which led to shrinking cannabis populations and separated strains to evolve differently, eventually creating the separate and distinct landrace strains of the european-evolved sativa and the asian-evolved indica.
by tracing the cannabis evolution back to a single location on the tibetan plateau millions of years ago, researchers have uncovered the site of the original cannabis landrace strain.