Around 2,500 years ago, at a cemetery high in the mountains of what’s now western China,
a group of people gathered for a funeral ritual.
They placed hot stones inside ten wooden containers scattered around the room,
then laid leaves on top of the stones.
As the leaves started to burn, they filled the enclosed space with a haze of smoke.
And, as the funeral-goers inhaled,
they found their minds being shifted to a new, peculiar state.
Thousands of years later, when archeologists analyzed the charred plant remains,
they realized they had stumbled upon the earliest known example of people smoking
a plant that over a hundred million still use in much the same way today: Cannabis.
But how did such a strange plant come to be in the first place?
When and where did we first domesticate it?
And why oh why does it get us high?
Well, the plant that manages to mysteriously hack
a biological system shared by almost all animals has undergone some hacks itself.
The story of cannabis evolution began around 420 million years ago.
Just kidding. Can you imagine?!
In reality, the deep time origins of cannabis had been, well, hazy, for a long time, thanks to the
fact that fossil prints of their distinctive leaves are extremely rare…only 2 are known.
But in recent years, analyses of specific DNA markers and studies
of fossil pollen have suggested that the genus got its start around 28
million years ago in the mid-Oligocene epoch, high on the Tibetan Plateau.
This is when it diverged from its sister genus Humulus,
which contains species commonly known as hops - a key ingredient to beer.
That family reunion must be lit.
And the formation of the Tibetan Plateau may actually have been a
key driver behind the origin of the plant itself.
See, cannabis thrives in what are known as steppe environments - open, arid, and tree-less habitats.
And when India collided with Asia around 35 million years ago, forming the Tibetan
Plateau, it caused those kinds of steppe environments to develop throughout the region.
This set the stage for Cannabis to emerge and flourish.
So, in a sense, plate tectonics gave us weed.
Following its lofty origins on the Tibetan Plateau,
the plant slowly spread both east and west, with its first fossil traces
appearing in Europe around 6 million years ago and eastern China around 1.2 million years ago.
By the time we humans arrived over a million years later,
Cannabis was already an ancient feature of many parts of Eurasia.
But it wasn't exactly like the cannabis we’re familiar with today,
which has been shaped by thousands of years of human cultivation and artificial selection.
Exactly how and when our relationship with this strange plant first began,
and how much we changed it over time, has been a mystery, for a few key reasons…
For one, we haven't been able to find any living populations of the wild ancestor,
if it even still exists at all.
Sure, there are plenty of places where cannabis grows in the wild today,
but all of those plants seem to be escaped lineages that were
once domesticated - making them feral, rather than truly wild.
In fact, the plant’s tendency to go feral and grow in the wild is where it got the nickname ‘weed.’
Plus, considering its use has been taboo in many cultures,
a lot of cannabis breeding has historically been done in secret.
And samples are often hard to legally collect,
making its domestication history difficult to reconstruct.
Additionally, we humans have found multiple uses for cannabis.
People not only grow it for its psychoactive properties,
but also use some lineages for their hemp fibers and oils.
In fact, for a long time,
taxonomists couldn’t agree on how many species of cannabis there even are today.
The current scientific view, though, is that there’s just one: Cannabis sativa,
which contains a variety of different cultivated lineages.
For all those reasons and more, tracing the details of the story
of people and pot using conventional methods proved extremely tricky.
But in 2021, researchers published a new study using methods that only
became available recently: genome sequencing.
They reconstructed the domestication history of Cannabis by comparing the genomes of 110 plants
from around the world - including feral lineages as well as those grown for both hemp and drugs.
And by looking at the genetic differences between the plants and using molecular
dating to work backwards, they were able to pinpoint a single origin of
Cannabis domestication in what's now China around 12,000 years ago.
This makes cannabis one of the single oldest known plants that we domesticated,
right around the dawn of the agricultural revolution itself.
For context, this means cannabis was domesticated
earlier than staples like wheat, corn and potatoes.
Priorities, right?
The genomic analysis also suggested that early domesticated cannabis was probably
first used as a multi-purpose crop, with the hemp and drug-type lineages
only separating from one another genetically around 4000 years ago.
This is when people began deliberately breeding different lineages for two different purposes,
leaving a strong signal of divergent selection in the genomes of each type.
The researchers were even able to pinpoint signals of selection on specific genes
responsible for the characteristic differences between the two types.
Like, for example, the genes responsible for the
taller and unbranched stems with higher fiber content of hemp-type cannabis.
And conversely, the genes behind the shorter, branching stems of drug-type
cannabis with woodier cores, more flowers, and greater resin production.
After these two cannabis types diverged around 4000 years ago, we start to find
clear archeological evidence of people using both types throughout Eurasia and beyond.
Multiple fiber artifacts from hemp-type cannabis appear in East Asia around this
time and spread westward into Europe and the Middle East.
The first clear evidence of people using drug-type cannabis to get high comes from
that mountain cemetery in western China 2,500 years ago, which researchers reported in 2019.
And written evidence from India indicates that
people were using drug-type cannabis as far back as 2000 years ago - with
it reaching Africa by the 13th century and Latin America by the 16th century.
Clearly, it’s a plant that we humans have had a very long history with.
But despite being able to figure out how and when we domesticated it,
why it gets us high in the first place is still pretty mysterious.
Is it just an accidental quirk of biochemistry,
or some kind of adaptive evolutionary strategy on the part of the plant itself?
And if so, what could that strategy originally have been?
Like, surely the plant doesn't want to be burned
and inhaled or baked into brownies by a species of bipedal ape, right??
Well, to dig into that question,
we first need to look at exactly how cannabis gets us high in the first place.
See, the primary molecule cannabis produces that’s responsible for its
psychoactive effects is called tetrahydrocannabinol, or THC.
And it’s just one of many chemicals that cannabis produces, which has led
it to being described as ‘the plant of a thousand and one molecules’.
Studies have shown that some of them have antimicrobial and
antifungal properties that help defend the plant against disease.
Others seem to act as a natural sunscreen, protecting the plant
from exposure to dangerous levels of ultraviolet radiation at high altitudes.
Which makes a lot of sense, seeing as its original Oligocene habitat
was on the Tibetan Plateau, where UV exposure is especially high.
Plus, there’s also evidence that these molecules help to deter some insect
pests and grazing herbivores, thanks to their off-putting taste and disorienting effects.
But we still don’t completely understand the full ecological
context that drove cannabis to become such a prolific chemist.
What we can say though, is that some of those molecules, like THC,
happen to be the right shape to bind to specific receptors in our
bodies - ones involved in what’s called the endocannabinoid system.
This is an ancient cell-signaling network that’s found in almost all animals,
from us primates to sea urchins, possibly dating back as far as 600 million years.
And the system uses a class of molecules produced by the body called endocannabinoids.
Many of them are similar to the ones cannabis produces,
and they regulate a wide range of important biological functions.
These include appetite, sleep, mood, learning and memory,
metabolism, and various aspects of overall growth and development.
Which means that animals had been producing and using cannabinoid molecules for hundreds of
millions of years before plants like cannabis independently evolved their own versions.
And these versions, like THC, mimic our own internally produced cannabinoids.
They bind to the same receptors and influence many of the functions we just mentioned,
resulting in the characteristic ‘high’ that cannabis gives its users.
So while the plant originally produced these molecules for a range of defensive roles,
we humans found their effects…intriguing.
And for thousands of years, through a process of careful and sometimes clandestine selection,
we’ve been further refining those effects,
making what was supposed to be a deterrent ever-more attractive.
So, because of its ability to hack an ancient cellular signaling system of animals,
cannabis became a favorite of many early cultures and a taboo in many modern ones.
Whatever your view on its use today,
cannabis is a plant that humans have been growing for longer than almost any other.
And one that we’ve been actively changing
for 12,000 years and counting, because of how it changes us.
Eons is a production of Complexly and if you like our channel,
we have a lot more stuff to share with you:
For instance, on SciShow, we’ve recently published a half hour long special on the
Bizarre Future of Telescopes that you have to see if you’re curious about what’s out there.
Scientists and engineers are building telescopes that span multiple continents, and brainstorming
far-out concepts like using craters on the moon as giant radio telescope dishes.
All in the hopes of seeing a little farther into the cosmos.
With these devices, we may learn more about the
beginning of our universe and whether we have company in it.
It’s an excellent video - check it out in the link in the description!
Now, cannabis is a flowering plant and before this group appeared - there were no flowers.
So check out our episode “When Did the First Flower Bloom?” to learn
when plants got a little bit more colorful - and it's also the first episode I hosted!
SIX YEARS AGO!
And high praise to this month’s Eontologists!
Jake Hart, Raphael Haase, Annie & Eric Higgins, John Davison Ng,
Melanie Lam Carnevale, Addie, Tony Dai, and Juan M
You can become an Eonite and help us make the show at patreon.com/eons.
And as always thank you for joining me in the Adam Lowe studio.
Subscribe at youtube.com/eons for more epic epochs.
The story of cannabis evolution began around 420 million years ago.
Just kidding. Can you imagine?!
[laughs]
The first time I read that line,
I didn't get to the joke part and I was like, "No f****** way! No f****** -
Oh yeah, no, no, no f****** way, it's a joke." [laughs]
Oh, that's brilliant.
Oh, you're gonna have to cut out so many giggles, Chris!
I've been trying to hold them to give you like three seconds... [laughs]
[laughs again]
Oh boy. [clears throat]