Chapter 1, 28 million years ago – 10,000 BCE, 12 min read
Before People: Where Cannabis Came From
Cannabis began as a wild grassland plant whose closest relative is the hop vine. Follow fossil pollen, DNA clocks, and ice ages back to its Asian origins.
By Professor High · Updated
- 1 Before People 28 million years ago – 10,000 BCE
- 2 First Farmers 10,000 – 2000 BCE
- 3 Smoke and Spirit 2000 BCE – 500 CE
- 4 Hashish and Hemp 500 – 1800
- 5 The Medicine Cabinet 1800 – 1900
- 6 Prohibition 1900 – 1961
- 7 Underground 1961 – 1995
- 8 The Great Reversal 1996 – November 2026
Cannabis began as a wild grassland plant in Asia, most likely on or near the northeastern Tibetan Plateau, and its closest living relative is the hop vine. Genetic clocks place the split from hops somewhere between about 16 and 29 million years ago. That is far older than any person who ever touched the plant. People did not invent cannabis, and nothing in the evidence says the plant evolved its chemistry for them.
Picture a reconstruction. A high, open plateau. There are no forests, only grass, gray-green wormwood, and low goosefoot weeds under a huge sky. Somewhere in that scrub, a cannabis-like plant sheds a cloud of pollen, and nothing there can write it down. That is where this story starts, and nobody was there to see it.
So this chapter works like a detective story with no eyewitnesses. The clues are a handful of fossils, a great deal of pollen, and DNA. We tell you which clue is which, how it was read, and how sure we are.
- 1 Before People 28 million years ago – 10,000 BCE
- 2 First Farmers 10,000 – 2000 BCE
- 3 Smoke and Spirit 2000 BCE – 500 CE
- 4 Hashish and Hemp 500 – 1800
- 5 The Medicine Cabinet 1800 – 1900
- 6 Prohibition 1900 – 1961
- 7 Underground 1961 – 1995
- 8 The Great Reversal 1996 – November 2026
What kind of plant is cannabis?
Cannabis belongs to the family Cannabaceae, a group of about 170 species that is mostly woody plants. Hops (genus Humulus) are cannabis’s sister genus. According to McPartland’s 2018 review of cannabis family history, the family also holds eight genera once filed under a separate family, the hackberries and their kin, including Celtis (hackberries) and Trema. Cannabis and hops are the odd ones out: soft-stemmed herbs sitting inside a family of woody relatives. One cousin, Parasponia, grows root nodules that fix nitrogen, a trick that legumes share and almost no other plant has.
Botanists have argued about where cannabis belongs for centuries. In 1583, Cesalpino first described the link between cannabis and hops. Later naturalists placed cannabis in the nettle or fig families. In 2003, DNA evidence led botanists to merge the hackberry family into Cannabaceae, and the family has stood that way since.
Hops make the best comparison. Hop cones carry resin glands, called lupulin glands, that make resins, bitter acids, and essential oils (Padgitt-Cobb and colleagues, 2023). Cannabis flowers carry resin glands of the same general kind. Hops are grown for brewing. Cannabis and hops also share a habit that shapes everything in this chapter: they mostly come in separate male and female plants.
Cannabis is an annual plant. It is wind-pollinated, and it is mostly dioecious, which means one plant is male and another is female. The sex comes from chromosomes, with XX for females and XY for males, the same system humans use (Ren and colleagues, 2021). Males mature five to six weeks before females (Dal Martello and colleagues, 2023). Males shed pollen into the wind. Females catch it. Female plants can sometimes grow male flowers, which our guide to hermaphrodite cannabis explains.
Wind pollination matters for the detective work. A plant that sheds pollen into the air leaves some of it behind in lake mud and bogs. Millions of years later, that pollen is still there to be counted.
Cannabis once had a sibling that did not survive. The paleobotanist Dorofeev found fruit fossils in central Siberia from an extinct genus in the cannabis family, now called Dorofeevia. They date to the Oligocene, about 34 to 23 million years ago. A later researcher, Collinson, re-examined them and agreed they belong to the family (McPartland, 2018). Cannabis’s family was larger once.
Oligocene, about 34 to 23 million years ago (the age is debated), Central Siberia (region approximate)
Cannabis loses a sibling
Fossil fruits from central Siberia show that an extinct genus, now named Dorofeevia, once stood beside cannabis and hops in the same family. The fruits date to the Oligocene, about 34 to 23 million years ago.
How can anyone know what happened 28 million years ago?
Scientists use four tools, and each one has a limit. You will meet all four again in later chapters, so it helps to know them now.
| Tool | What it tells us | Its limit |
|---|---|---|
| Fossils of leaves or fruit | Shows the plant was there, in that rock | Cannabis leaf and fruit fossils are very rare: only 3 are known worldwide |
| Fossil pollen | Shows where a plant group grew, and roughly when | Cannabis and hop pollen look alike |
| Molecular clock | Gives a date for when two lineages split | The date depends on assumptions and on the fossils used to calibrate it |
| Radiocarbon dating | Dates once-living material from the last 50,000 years or so | Cannot reach back millions of years |
Start with pollen. Pollen grains are tiny and tough. They settle on lakes and bogs, sink into the mud, and stay there layer after layer. When scientists pull up a core of that mud and count the grains in each layer, they can reconstruct which plants grew nearby and when (U.S. Geological Survey). Deeper layers are older.
Here is the catch. Cannabis and hop pollen look very much alike. Both are triporate, meaning each grain has three small pores, a trait they inherited from a shared ancestor (McPartland, 2018). Many pollen studies therefore report only “Cannabis/Humulus” and stop there.
So some researchers read the neighbors. If the mystery grains sit with grasses, wormwood, and goosefoot pollen, the landscape was steppe, and the grains probably came from cannabis. If they sit with alder, willow, and poplar, the landscape was forest, and the grains probably came from hops. If they surge upward at the same time as crop pollen, they probably came from cultivated hemp (McPartland, Guy, and Hegman, 2018). It is clever, and it is an inference. A grain is never proven to be cannabis by this method. Keep that in mind for every pollen date below.
Next, the molecular clock. DNA picks up random changes at a fairly steady pace, so the number of differences between two living species hints at how long ago they split. The clock needs a time check, so researchers set it with fossils of related plants whose ages are known (McPartland, 2018). A different set of fossils or genes gives a different answer. We will see that right away.
Finally, radiocarbon. Living things take in carbon-14. At death they stop, and the carbon-14 slowly decays. Measure what is left, and you can date the material. The method is good for about 50,000 years, and it dates the organism, not the day a person used it (Oxford Radiocarbon Accelerator Unit). Radiocarbon dates carry the label BP, “before present,” where present means 1950. A tree-ring record turns them into calendar dates, written “cal BP” (ORAU calibration). Radiocarbon helps with the last pages of this chapter and most of the next ones. It cannot help with the deep past.
Where did cannabis begin?
The best-supported guess is the northeastern Tibetan Plateau, but it is a guess built from several indirect clues. The first clue is the clock. A chloroplast DNA analysis by McPartland and Guy, set with four fossil dates and reported in the 2018 review, put the split between cannabis and hops at 27.8 million years ago.
c. 28 million years ago (estimates run from 16 to 29), Northeastern Tibetan Plateau (hypothesized)
Cannabis splits from hops
A DNA clock calibrated with fossils of related plants puts the split between cannabis and hops at 27.8 million years ago. Pollen maps place the birthplace on the northeastern Tibetan Plateau. The date is better supported than the place.
Sources (3)
- McPartland 2018, Cannabis Systematics at the Levels of Family, Genus, and Species, Cannabis and Cannabinoid Research 3(1):203-212
- McPartland, Hegman and Long 2019, Cannabis in Asia: its center of origin and early cultivation, Vegetation History and Archaeobotany 28:691-702
- Zhang et al. 2018, Latitudinal Adaptation and Genetic Insights Into the Origins of Cannabis sativa L., Frontiers in Plant Science 9:1876 (a rival, low-latitude view)
A 2023 hop genome study gives a younger date. Its best relaxed-clock model puts the split at about 22.6 million years ago, with a 95% range of 15.7 to 28.8 million years. The authors say their estimates agree with earlier ones (18.2 to 27.8 million years) and call the date “a source of debate” (Padgitt-Cobb and colleagues, 2023). The honest summary: somewhere between 16 and 29 million years ago.
c. 23 million years ago (95% range 15.7 to 28.8 million), No single place (dated from DNA)
A newer clock gives a younger split
A 2023 hop genome study gives a younger date: about 22.6 million years ago, with a 95% range of 15.7 to 28.8 million. The authors say it agrees with earlier estimates and call the date "a source of debate."
The second clue is the oldest pollen that fits cannabis. In a survey that added 155 Asian pollen studies, the oldest grains in a steppe-type mix (grass, wormwood, and goosefoot pollen) came from northwestern China and date to about 19.6 million years ago (McPartland, Hegman, and Long, 2019).
c. 19.6 million years ago, Northwestern China (Ningxia region, approximate)
The oldest pollen that fits cannabis
In steppe-type pollen mixes from northwestern China, the oldest grains consistent with cannabis date to about 19.6 million years ago. Hop pollen looks nearly the same, so scientists read the neighboring plants as clues.
There is an eight-million-year gap between the clock date and the oldest pollen. The researchers bridged it by tracing the earliest wormwood pollen. Their maps converge on the northeastern Tibetan Plateau, near Qinghai Lake, where the first steppe community of Asia appeared. They conclude that cannabis began there (McPartland, Hegman, and Long, 2019).
Read that carefully. It comes mainly from one research group, and it rests on pollen that cannot be told apart from hop pollen by shape alone. A different team studied chloroplast DNA from 645 plants. Their oldest-branching lineage lives at low latitudes, which hints at a more southern origin (Zhang and colleagues, 2018). Many biogeographers have named Central Asia instead. The Tibetan Plateau is a leading hypothesis, not a settled fact.
How did cannabis reach Europe, and how did it survive the ice?
Fossil pollen suggests cannabis spread west millions of years before farming, with no human help. That runs against the usual story, in which people carried cannabis to Europe and Scythian riders, around 700 BCE, are often implicated (McPartland, Guy, and Hegman, 2018).
A 2019 follow-up from the same group says cannabis reached Europe by about 6 million years ago (McPartland, Hegman, and Long, 2019). Both figures are “by” dates from the same group: the 2018 pollen gives 1.8 to 1.2 million years, and the 2019 paper gives about 6 million. The 2019 paper places one reported fossil in its westward-spread argument: a single fruit from Bulgaria, labeled “Cannabis sp.” by its finder and dated to the end of the Miocene, 7.3 to 5.3 million years ago. It rests on one identification (McPartland, 2018).
7.3 to 5.3 million years ago (end of the Miocene), Bulgaria (region approximate)
One fruit fossil in Bulgaria
A single fruit fossil from Bulgaria, labeled "Cannabis sp." by its finder, dates to the end of the Miocene, 7.3 to 5.3 million years ago. The 2019 paper uses it in its westward-spread argument. It rests on one identification.
The oldest European pollen is older than our own species. It dates to 1.8 to 1.2 million years ago and comes from the upper Volga River basin in Russia, in a meta-analysis of 479 European pollen studies, plus 36 from older layers (McPartland, Guy, and Hegman, 2018).
1.8 to 1.2 million years ago, Upper Volga River basin, Russia (approximate)
Cannabis-type pollen reaches Europe
A meta-analysis of European pollen studies finds cannabis-type pollen in the upper Volga basin dated to 1.8 to 1.2 million years ago. That is older than Homo sapiens, which challenges the idea that people carried cannabis west.
Sources (2)
A 2019 survey reports cannabis-type pollen in South Asia by about 32,600 years ago. The authors note that Celtis (hackberry) pollen looks similar and that some earlier South Asian reports may have confused the two. We mark it low confidence.
by about 32,600 years ago, India (region approximate)
Cannabis-type pollen in South Asia
A 2019 pollen survey reports cannabis-type pollen in South Asia by about 32,600 years ago. The authors warn that hackberry (Celtis) pollen looks similar and that earlier reports may have confused the two.
Then came the ice. Nearly all the great ice sheets sat at their maximum extent from about 26,500 to about 19,000 or 20,000 years ago (Clark and colleagues, 2009). In Europe, the ice edge lay between about 52 and 56 degrees north. Trees fled to refuges in the south, below about 45 degrees north. Between those latitudes lay cold, dry steppe and tundra, and the pollen maps show a belt of cannabis-type pollen running across Europe there (McPartland, 2018).
Last Glacial Maximum, about 26,500 to 19,000 years ago, Europe between about 45 and 56 degrees north
A belt of steppe plants below the ice
Between the ice edge and the southern tree refuges, pollen maps show a belt of cannabis-type pollen across Europe. Cold, dry steppe and tundra suited the plant while ice sheets stood at their maximum.
When the climate warmed, forest took over from steppe. Well after this chapter’s end, in the warm, wet period 7,000 to 6,000 years ago, the pollen record shifts toward hop-type forest plants, and cannabis retreats to steppe refuges on the Pontic steppe, north of the Black Sea, and along the Mediterranean coast. The pattern repeated through several cold-and-warm cycles. Each time, the cannabis population shrank to small numbers, and small populations drift genetically. McPartland argues that repeated bottlenecks and genetic drift likely started the split between European and Asian cannabis lineages (McPartland, 2018).
That idea is a hypothesis. If it holds, the European-versus-Asian split in cannabis is much older than any breeder. Our guide to pure indica and sativa strains covers what DNA tests say about today’s labels.
Myth check Disputed
The claim: “People carried cannabis to Europe. Before farmers arrived, it did not grow there.”
Pollen studies suggest wild-type cannabis grew in Europe long before farming, even before Homo sapiens. But the method reads neighboring plants as clues, and one research group produced most of this work. "Native to Europe" is a strong hypothesis, not a settled fact.
Hypothesized origin: northeastern Tibetan Plateau. Near Qinghai Lake. A hypothesis built from pollen maps and a molecular clock. A rival DNA study points to lower latitudes. The circle is schematic.
Why would a plant make THC and CBD?
Nobody knows for sure. The leading ideas are that the resin protects the plant from sun, insects, grazers, and microbes. A recent review of cannabis resin glands says the exact benefit of cannabinoids and terpenes for the plant “has yet to be discovered.”
First, a detail that surprises people. The plant mostly makes the acid forms, THCA and CBDA, in glandular trichomes, the tiny stalked glands on female flowers. Fresh flower holds relatively little THC and CBD and more of the acids. Over time, and faster with heat and light, the acids convert to THC and CBD (Tanney and colleagues, 2021). A trichome stores its resin in a cavity above the secretory cells, and one team found that the enzyme that makes THCA is secreted into that cavity (Sirikantaramas and colleagues, 2005). THCA can harm plant cells, so the cavity may act as a safe storage vault (Tanney and colleagues, 2021). Our trichome guide shows how they look on a real flower.
Now the hypotheses. Each one gets a label.
- Sun shield. Plants at high altitude get more ultraviolet-B light, and one hypothesis ties cannabinoids to the Tibetan uplift (McPartland, 2018). Early studies reported more THC under strong UV-B (reviewed by Tanney and colleagues, 2021). But indoor trials found no gain from UV in modern cultivars. In one cultivar, yield and THC fell as UV rose (Rodriguez-Morrison and colleagues, 2021). In another, UV had no effect on yield or cannabinoids (Llewellyn and colleagues, 2022). Those tests used modern, bred plants, so they cannot rule out an ancient role. This idea is the weakest of the three.
- Grazer defense. As steppe spread, so did animals that eat cannabis today: horses and their kin, rodents, rabbits and pikas, and pigeons. Cannabinoids might make cannabis a bad meal (McPartland, 2018).
- Insect and microbe defense. In lab tests, THCA and CBGA kill cultured insect cells, and thick resin may trap small insects. Several cannabinoids also show antibacterial activity in the lab (Tanney and colleagues, 2021).
The same review warns that researchers still need to show that these compounds are more than by-products of other processes. No one can test an ancient plant, so the best answer is “defense is the leading idea, and it is unproven.”
Myth check False
The claim: “Cannabis evolved THC to get people high.”
No evidence supports this. The plant's reason for making cannabinoids is unknown. Leading ideas are defense against insects, grazers, microbes, and sunlight. The cannabis lineage split from hops 16 to 29 million years ago. The earliest find we could date with confidence is about 10,000 years old, and older pottery-linked claims are disputed.
Wild, feral, and the first meeting with people
Truly wild cannabis may no longer exist. Plants growing unaided along roads are feral, which means they descend from crop plants that escaped. Escaped plants regain a wild-type look in as little as 50 generations (McPartland, 2018), so a weedy roadside plant looks wild but is not the original.
The 2021 genome study sequenced 110 plants from around the world. All the feral plants it studied traced back to escaped crops. The authors say their results would suggest that pure wild ancestors of cannabis have gone extinct (Ren and colleagues, 2021). Outside experts and the authors note gaps. Plant geneticist Nolan Kane called the data “a phenomenal resource.” The study had no samples from Afghanistan or Russia, and the authors write that additional sampling of feral plants “is still needed.” Plant biologist Jonathan Page said, “East Asia is a big place, it may exist” (Smithsonian Magazine, 2021).
Myth check True, but
The claim: “Cannabis that grows by itself along roads is wild.”
It grows without help, but DNA shows the plants studied descend from escaped crops. They are feral, not original wild plants. Escaped plants regain a wild look in as few as 50 generations. Truly wild ancestors may be extinct, though outside experts note sampling gaps.
How did people first meet this plant? Nobody knows, and the earliest find we could date with confidence is about 10,000 years old (Okinoshima, 8280 to 7660 cal BCE). Ren and colleagues (2021) also cite older pottery-linked finds, which are disputed. Seeds and fibre rarely survive, so absence of evidence is weak evidence.
One idea has been around for a century. Cannabis grows well in nitrogen-rich soil and invades freshly disturbed ground. Researchers have hypothesized that its original habitat was open, sunny ground, and that streams visited by herds supplied the nitrogen. That led to the “camp follower” hypothesis: cannabis may have sprouted on rubbish heaps near human settlements, and people may have started to use the volunteer plants (Vavilov, 1926; Anderson, 1952, as summarized by Dal Martello and colleagues, 2023). It is a hypothesis. It fits the plant’s habits, but we know of no excavation that has tested it.
If people did take it up, seeds may have drawn them. They are food, and food use leaves a better archaeological trail than fibre (Dal Martello and colleagues, 2023).
That brings us to the doorstep of domestication. By comparing whole genomes, the Ren team estimated that early domesticated lineages split from the basal, wild-like lineage about 12,000 years ago, with a 95% range from 6,458 to 15,728 years ago. They place this in early Neolithic East Asia (Ren and colleagues, 2021). Cannabis fruits from Okinoshima in Japan, which chapter 2 covers, are directly dated to 8280 to 7660 cal BCE, a date inside the clock’s wide range. Dal Martello’s review calls them “some of the earliest finds of cannabis in the world.” The two dates are not the same kind of date. One comes from a molecular clock, the other from radiocarbon on real seeds. They agree on the neighborhood, not the street address.
about 12,000 years ago (95% range 15,728 to 6,458), East Asia (broad region; no single site)
The doorstep of domestication
Genomes from 110 plants suggest hemp and drug lineages split from a basal, wild-like lineage about 12,000 years ago, in early Neolithic East Asia. The 95% range runs from about 15,700 to 6,500 years ago.
Sources (2)
Check your understanding
3 questions. Pick an answer in your head, then open the question to check it.
1 Which plant is cannabis's closest living relative, its sister genus?
- AHackberry trees
- BHops
- CStinging nettle
- DTobacco
Answer: B. Hops
Cannabis and hops (Humulus) are sister genera in the family Cannabaceae. Hackberries belong to the family too, but they are more distant cousins.
2 Why do scientists check the neighboring plants when they find cannabis-type pollen?
- ACannabis pollen glows under ultraviolet light
- BCannabis and hop pollen look almost the same, so the neighbors give clues
- CCannabis pollen only appears next to crop pollen
- DRadiocarbon dating needs the neighbors to work
Answer: B. Cannabis and hop pollen look almost the same, so the neighbors give clues
Grass, wormwood, and goosefoot neighbors point to steppe cannabis. Alder, willow, and poplar neighbors point to forest hops. It is an inference, not proof.
3 What does the 110-plant genome study suggest about cannabis that grows by itself along roads?
- AIt is the original wild ancestor
- BIt is feral, descended from escaped crop plants
- CIt is a separate species
- DIt only grows in Europe
Answer: B. It is feral, descended from escaped crop plants
All the feral plants studied descend from escaped crops. The authors say pure wild ancestors may be extinct, though outside experts note gaps in the sampling.
0 of 3 answered
By the end of this chapter, cannabis has grown from a lone grassland weed to a wide-ranging plant with a sister genus, a story told in pollen, and a puzzling chemistry. Humans have not yet picked it up on purpose. In Chapter 2, “First Farmers: Hemp in the Neolithic,” we meet the people who did: potters in Japan, villagers in China, and the cord and cloth that made hemp one of the first crops.
Go deeper
- Landrace Strains: Original Cannabis Genetics That Started It All Explore landrace cannabis strains—the ancient genetics from Afghanistan to Thailand that shaped every modern hybrid you love today.
- Cannabis Trichomes: Types, Maturity, and Reading Quality What cannabis trichomes are, the 3 types, how they make cannabinoids and terpenes, the clear-cloudy-amber harvest window, and reading flower quality.
- Cannabis Ruderalis: The Genetics Behind Autoflowering Meet Cannabis ruderalis, the hardy weed from Russia and Central Asia whose day-neutral flowering gene became the backbone of every modern autoflower strain.
- Are There 100% Indica or 100% Sativa Strains? What DNA Tests Found A strain sold as 100% sativa matched a reported 100% indica in a DNA study. What pure indica or sativa can mean, and why a menu label cannot prove it.
Sources
Every placard and myth check in this chapter cites at least one of these. We rate how sure each claim is on its placard.
- McPartland 2018, Cannabis Systematics at the Levels of Family, Genus, and Species, Cannabis and Cannabinoid Research 3(1):203-212 Cited for: Cannabis loses a sibling; Cannabis splits from hops; The oldest pollen that fits cannabis; One fruit fossil in Bulgaria; Cannabis-type pollen reaches Europe; A belt of steppe plants below the ice; Myth: People carried cannabis to Europe. Before farmers arrived, it did not grow there.; Myth: Cannabis evolved THC to get people high.; Myth: Cannabis that grows by itself along roads is wild.
- McPartland, Hegman and Long 2019, Cannabis in Asia: its center of origin and early cultivation, Vegetation History and Archaeobotany 28:691-702 Cited for: Cannabis splits from hops; The oldest pollen that fits cannabis; Cannabis-type pollen in South Asia
- Zhang et al. 2018, Latitudinal Adaptation and Genetic Insights Into the Origins of Cannabis sativa L., Frontiers in Plant Science 9:1876 (a rival, low-latitude view) Cited for: Cannabis splits from hops
- Padgitt-Cobb et al. 2023, An improved assembly of the Cascade hop genome ... refines time of divergence estimates for the Cannabaceae family, Horticulture Research 10:uhac281 Cited for: A newer clock gives a younger split; Myth: Cannabis evolved THC to get people high.
- McPartland, Guy and Hegman 2018, Cannabis is indigenous to Europe and cultivation began during the Copper or Bronze age, Vegetation History and Archaeobotany 27:635-648 Cited for: Cannabis-type pollen reaches Europe; Myth: People carried cannabis to Europe. Before farmers arrived, it did not grow there.
- Clark et al. 2009, The Last Glacial Maximum, Science 325:710-714 (dates of the ice maximum) Cited for: A belt of steppe plants below the ice
- Ren et al. 2021, Large-scale whole-genome resequencing unravels the domestication history of Cannabis sativa, Science Advances 7(29):eabg2286 Cited for: The doorstep of domestication; Myth: Cannabis that grows by itself along roads is wild.
- Dal Martello et al. 2023, Morphometric approaches to Cannabis evolution and differentiation from archaeological sites, Vegetation History and Archaeobotany Cited for: The doorstep of domestication
- Tanney et al. 2021, Cannabis Glandular Trichomes: A Cellular Metabolite Factory, Frontiers in Plant Science 12:721986 Cited for: Myth: Cannabis evolved THC to get people high.
- Smithsonian Magazine 2021, New Study Suggests Cannabis' Wild Ancestors Likely Came from China Cited for: Myth: Cannabis that grows by itself along roads is wild.
