@Fenderbender said, "Indica & Sativa diverged a million years ago."
Coming back now to what Fenderbender said...
It may be true... way back in 2010, McPartland and Guy did a "molecular clock" type test on cannabis DNA...
"They estimated that
Humulus and
Cannabis diverged from a common ancestor 27.8 mya.
C. sativa and Cannabis indica diverged 1.05 million years ago, but this was not published because the taxa differ at only one nucleotide site." [
source ]
But notice that last bit... "the taxa differ at only one nucleotide site." I think that means one base pair in the DNA of the genome, of which there are over 800 million base pairs. Well, that surely isn't showing a distinction between sativa and indica biotypes.
This lead me to another study, published by the University of Toronto in 2018, which found evidence in the DNA related to the difference between THC-producing cannabis and CBD-producing cannabis, as a result of gene duplication and invading viruses...
"The enzymes making THC and CBD are encoded by THCA and CBDA synthase genes, respectively. Both are found on chromosome 6 of the ten chromosomes the cannabis genome is packaged into.
• • •
The gene sequences for the THCA and CBDA synthases are nearly identical supporting the idea that they come from the same gene which was duplicated millions of years ago. Over time, one or both gene copies became scrambled by invading [viruses], and by evolving separately, they eventually came to produce two different enzymes -- CBDA synthase found in hemp (fibre-type), and THCA synthase in drug-type (marijuana)."
I believe this can be viewed as an ancient (pre-human) emergence of the THC-producing biotype from the CBD-producing biotype.
Let's suppose for the moment that the divergence of sativa and indica did happen about 1 million years ago, and that viral attack coupled with evolutionary adaptation gave rise to THC production. What was also happening 1 million years ago?
The ice age of the Pleistocene Era started 1.6 million years ago, so 1 million years ago is about one third of the way into the ice age.
From an article by Sensi Seeds, 2020, titled "The Evolution of Cannabis Sativa & the Cannabis Ancestor":
"[during the ice age]...vast swathes of the planet iced over. Continental glaciers (vast ice sheets that cover entire land masses all the way to sea level) stretched as far as 40 degrees latitude from the poles, and thousands of plant and animal species went extinct, or were pushed into “refuges” that provided favourable enough conditions for survival.
• • •
The Cannabis genus was lucky enough to survive, and it is thought that it did so by occupying various refuges in Central and Southern Asia. There is little doubt among scientists that this period would have seen some of the most dramatic evolutionary change within the genus, as it rushed to produce genotypes that would survive in a radically different set of habitats. It is thought that the adaptations that led to the development of “sativa”, “indica” and “ruderalis” biotypes is likely to have occurred during this time.
It is also believed that during this time, the cannabis plant gained the ability to produce THC, due to a mutation in the cannabinoid synthase gene. Thus, by the time cannabis began to split off into the types that we know today, it already had the ability to produce THC. The evolutionary pressures acting on it since then, both human and environmental, have influenced how much THC the various populations produce."
Now let's think back again to the Oligocene cannabis of 28 mya in the subtropical environment of what would become the Tibetan Plateau, which split from
humulus (hops) around that time, and may have resembled
Humulus japonicus with its cannabis-like leaves. And remember, the plateau rose for a period of 5 million years, which may have gradually caused the natural selection of THC production and the emergence of the indica biotype. That would have happened between 28 and 23 million years ago. (Since 23 mya is the beginning of the Miocene Period, we could call this adapted biotype,
Miocene cannabis.)
So which is it... sativa and indica split around 1 million years ago, or they split between 28 and 23 million years ago?
Could the Oligocene cannabis have survived and evolved as the Tibetan Plateau rose to its present-day elevation?
I wrote earlier in this thread: "...The possible epicenter of cannabis ("center of origin"), eastern Tibetan Plateau, near
Qinghai Lake, elevation 10,500 ft., according to the 2019 study by McPartland, Hegman, and Long."
According to Sharma (1977), cannabis grows up to 10,000 ft in the Himalayas, and apparently its THC potency tends to increase with elevation.
So, yes... the Oligocene cannabis of the Tibetan Plateau may have evolved into the Miocene cannabis.
EDIT: If only it were possible to do a DNA analysis of Oligocene cannabis vs. the Miocene cannabis!