Humans have been consuming cannabis for millennia, but scientists are still largely in the dark about the devil’s lettuce.
Why does marijuana get you high? Unless you’re currently high, you probably know the psychoactive properties of weed are linked to an active compound called tetrahydrocannabinol, or THC. So the wired question becomes: Why does marijuana have THC in the first place?
Thus far in history, only one other natural chemical creates a similarly intoxicating experience — a little-known liverwort from New Zealand. For decades, researchers have speculated that the cannabis plant produces THC to aid in its own survival.
There’s no questioning that this is true. For one, the compound seems to act as a built-in sunscreen, shielding delicate leaves and flowers from harsh UV-B lightwaves. Secondly, the cannabinoid is a potent natural anti-microbial and insect repellent, protecting flowers from pests and infection.
Here’s where things get weird. The cannabis plant may not have developed the ability to produce THC on its own. Instead, recent science suggests that the herb borrowed the DNA from other organisms. Most notably, the cannabis plant took inspiration from ancient gene-scrambling viruses. This biological borrowing, as it turns out, may be the reason why intoxicating cannabis and CBD-rich hemp separated from one another.
A team of researchers created the world’s first cannabis chromosome map, revealing how, millions of years ago, viruses colonized one of marijuana’s 10 chromosomes, where enzyme genes that produce THC and CBD exist. One or both of those genes was overwhelmed by DNA maligned by the viruses, and that viral DNA eventually spread throughout the cannabis genome.
Through the use of a cannabis genome map, scientists determined how the species evolved into two separate strains with distinct chemical properties: hemp and marijuana. Pot became potent in when its genome was colonized by a virus-like force called retroelements.
The Origins of THC
It turns out, cannabis aficionados all over the globe have an accident to thank for the development of THC.
After completing an exhaustive sequence of the cannabis genome, researchers from the University of Toronto, the University of British Columbia, and the Icahn School of Medicine at Mt Sinai in New York found that the world’s favorite herb inherited its ability to produce the psychoactive after a series of infections millions of years ago.
Viral invasions of the genome are nothing new, most plant species contain millions of garbled fragments of their own DNA mixed with that of viruses. These infectious viral entities are called retrotransposons, and they’re sometimes referred to as “genetic parasites”.
Remnants of these genetic parasites, called retroelements can be passed along from generation to generation — a heritable trait that, at first glance, doesn’t seem to follow the rules of natural selection. Instead of developing the ability to produce THC automatically for its own benefit, the cannabis plant got a little help.
This viral help not only made the plant more appealing to humans later down the line, but it also split the cannabis plant into two generalized chemovars: intoxicating marijuana and fibrous hemp.
“The proteins [for THC and CBD] are embedded in this huge mess of virus-like sequences,” said Tim Hughes, a professor of molecular genetics at the University of Toronto and co-author of the study. “One thing that these sequences are known for is facilitating the rearrangement of the chromosome, and they’re actually a bit dangerous in that way.”
According to Hughes, these viruses could have accelerated an evolutionary process that resulted in a single enzyme gene in cannabis mutating into two, eventually giving us THC and CBD. “It’s easy to imagine that, over a long time scale, this process happened over and over again in this part of the chromosome where these two enzymes are,” he said.
Ancient Viruses Cause Split Between Cannabis and Hemp
Prior to infection, there is no indication that the plant could produce either THC or CBD as two unique chemical compounds. Instead, the cannabis plant seems to only have had one enzyme that perhaps made chemicals that were similar in structure to either cannabinoid. After infection, the virus DNA coupled with natural DNA replication split the genetic makings of one enzyme into two, allowing certain plants to produce either THC or CBD.
It is important to quickly point out, however, that it’s technically incorrect to say that these viruses allowed the plant to produce THC. Instead, the viral infection enabled the plant to produce THC-acid. This acid then converts to THC slowly after exposure to heat and the elements. The cannabis plant synthesizes THC-A using an enzyme, which is a special protein that facilitates the chemical reaction that puts THC-acid together.
It’s this enzyme, along with the enzyme that produces CBD-acid, that the ancient viral infection seemed to create. After viruses made themselves at home millions of years ago, it caused the enzymes that make either THC-A or CBD-A to drift apart.
Over time, the research scientists presume, these different plants were selectively bred by humans, who relied on both plant varieties for food, fiber, medicine, and spiritual purposes. An amazing fact, considering that without infection, these revered molecules may have never come into creation.
It’s hard to say what cannabis was like before ancient viruses helped it develop the properties we’re familiar with today, but according to Hughes some of its closest relatives are innocuous plants like mulberry and hops.