Cannabis is indigenous to Europe and cultivation began during the Copper or Bronze age: a probabilistic synthesis of fossil pollen studies

Abstract

Conventional wisdom states Cannabis sativa originated in Asia and its dispersal to Europe depended upon human transport. Various Neolithic or Bronze age groups have been named as pioneer cultivators. These theses were tested by examining fossil pollen studies (FPSs), obtained from the European Pollen Database. Many FPSs report Cannabis or Humulus (C/H) with collective names (e.g. Cannabis/Humulus or Cannabaceae). To dissect these aggregate data, we used ecological proxies to differentiate C/H pollen, as follows: unknown C/H pollen that appeared in a pollen assemblage suggestive of steppe (Poaceae, Artemisia, Chenopodiaceae) we interpreted as wild-type Cannabis. C/H pollen in a mesophytic forest assemblage (Alnus, Salix, Populus) we interpreted as Humulus. C/H pollen curves that upsurged and appeared de novo alongside crop pollen grains we interpreted as cultivated hemp. FPSs were mapped and compared to the territories of archaeological cultures. We analysed 479 FPSs from the Holocene/Late Glacial, plus 36 FPSs from older strata. The results showed C/H pollen consistent with wild-type C. sativa in steppe and dry tundra landscapes throughout Europe during the early Holocene, Late Glacial, and previous glaciations. During the warm and wet Holocene Climactic Optimum, forests replaced steppe, and Humulus dominated. Cannabis retreated to steppe refugia. C/H pollen consistent with cultivated hemp first appeared in the Pontic-Caspian steppe refugium. GIS mapping linked cultivation with the Copper age Varna/Gumelniţa culture, and the Bronze age Yamnaya and Terramara cultures. An Iron age steppe culture, the Scythians, likely introduced hemp cultivation to Celtic and Proto-Slavic cultures.

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Vegetation History and Archaeobotany (2018) 27:635–648
https://doi.org/10.1007/s00334-018-0678-7
REVIEW
Cannabis isindigenous toEurope andcultivation began
duringtheCopper orBronze age: aprobabilistic synthesis offossil
pollen studies
JohnM.McPartland1,2 · GeoreyW.Guy2· WilliamHegman3
Received: 22 October 2017 / Accepted: 9 April 2018 / Published online: 5 May 2018
© Springer-Verlag GmbH Germany, part of Springer Nature 2018
Abstract
Conventional wisdom states Cannabis sativa originated in Asia and its dispersal to Europe depended upon human transport.
Various Neolithic or Bronze age groups have been named as pioneer cultivators. These theses were tested by examining
fossil pollen studies (FPSs), obtained from the European Pollen Database. Many FPSs report Cannabis or Humulus (C/H)
with collective names (e.g. Cannabis/Humulus or Cannabaceae). To dissect these aggregate data, we used ecological prox-
ies to differentiate C/H pollen, as follows: unknown C/H pollen that appeared in a pollen assemblage suggestive of steppe
(Poaceae, Artemisia, Chenopodiaceae) we interpreted as wild-type Cannabis. C/H pollen in a mesophytic forest assemblage
(Alnus, Salix, Populus) we interpreted as Humulus. C/H pollen curves that upsurged and appeared de novo alongside crop
pollen grains we interpreted as cultivated hemp. FPSs were mapped and compared to the territories of archaeological cul-
tures. We analysed 479 FPSs from the Holocene/Late Glacial, plus 36 FPSs from older strata. The results showed C/H pol-
len consistent with wild-type C. sativa in steppe and dry tundra landscapes throughout Europe during the early Holocene,
Late Glacial, and previous glaciations. During the warm and wet Holocene Climactic Optimum, forests replaced steppe,
and Humulus dominated. Cannabis retreated to steppe refugia. C/H pollen consistent with cultivated hemp first appeared in
the Pontic-Caspian steppe refugium. GIS mapping linked cultivation with the Copper age Varna/Gumelniţa culture, and the
Bronze age Yamnaya and Terramara cultures. An Iron age steppe culture, the Scythians, likely introduced hemp cultivation
to Celtic and Proto-Slavic cultures.
Keywords Cannabis sativa· Humulus lupulus· European Pollen Database· Europe· GIS· Pleistocene· Holocene
Introduction
Linnaeus (1737) knew Cannabis sativa as a cultivated plant
in Europe, so he assumed its centre of origin (CoO) was
elsewhere. He suggested a CoO in India Orientali (encom-
passing the Indian subcontinent, southeastern Asia, and the
Malay Archipelago), Japonia (Japan), or Malabaria (the
Malabar coast of southwest India). Most scholars concur
with de Candolle (1883) who offered Central Asia as the
CoO of C. sativa. He collated linguistic, historical, archaeo-
logical, and palaeontological data, as well as “in what coun-
try it grows spontaneously and without the help of man”. He
proposed that C. sativa expanded to Europe under the aegis
of human transport around 1500 bce, and he implicated the
Scythians.
Some botanists placed the CoO of C. sativa in Europe
(Thiébault de Berneaud 1835; Keppen 1886), or a CoO
spanning Asia and Europe (Herder 1892; Vavilov 1926).
Communicated by F. Bittmann.
Electronic supplementary material The online version of this
article (https ://doi.org/10.1007/s0033 4-018-0678-7) contains
supplementary material, which is available to authorized users.
* John M. McPartland
mcpruitt@myfairpoint.net
1 University ofVermont, Burlington, VT, USA
2 GW Pharmaceuticals, Sovereign House, Histon,
CambridgeCB249BZ, UK
3 Department ofGeography, Middlebury College, Middlebury,
VT05753, USA

636 Vegetation History and Archaeobotany (2018) 27:635–648
1 3
Lamarck (1785) recognized two species, C. sativa and C.
indica. He suggested that C. sativa grew croît naturelle-
ment in Persia and presque naturalisée in Europe, whereas
C. indica originated in India. Many botanists treat these taxa
as subspecies, C. sativa ssp. sativa, and C. sativa ssp. indica
(Small and Cronquist 1976). Winterschmidt (1818) recog-
nized two species, C. sativa and C. chinensis, with their
CoOs in Russia and Ostindien, respectively.
De Candolle limited his palaeontological evidence to
print fossils (impressions of leaves or fruits in rocks), and
not fossil pollen (accurately, subfossil pollen). Reports of
print fossils of C. sativa have not been convincing (four
reported world-wide), with one exception (Palamarev 1982).
Conversely, hundreds of fossil pollen studies (FPSs) across
Eurasia have identified Cannabis pollen. Researchers have
utilized this database to track the cultivation history of C.
sativa in Europe and Asia. Dörfler (1990) analysed 77 Euro-
pean FPSs conducted by himself and others. He concluded
that hemp cultivation began in west-central Europe by the
Iron age. Clarke and Merlin (2013) reviewed 133 European
FPSs. They concluded that C. sativa diffused from Asia to
Europe during the Bronze age. Long etal. (2017) synthe-
sized 46 FPSs in their pan-Eurasian study. They also con-
cluded that C. sativa diffused from Asia to Europe during
the Bronze age.
All three meta-analyses (Dörfler, Clarke and Merlin,
Long etal.) corroborated FPS data with archaeobotanical
evidence—seed, fiber, cordage, textiles, and pottery impres-
sions or pseudoliths of the same. We have also examined
archaeobotanical evidence, published separately (McPart-
land and Hegman 2017). Robust archaeobotanical evidence
identified the Bronze age Yamnaya culture as an early adop-
ter of C. sativa, in southeastern Europe.
The purpose of this study is to revisit European FPSs,
by accessing an expanded database, and using a different
pollen identification method. Unlike previous studies (Dör-
fler 1990; Clarke and Merlin 2013; Long etal. 2017), we
included FPSs that analysed strata anterior to the Holocene
epoch. As de Candolle (1883) stated, “conditions anterior to
our epoch determined the greater number of the facts of the
actual distribution of plants”. Examining pollen from earlier
epochs will address the question of C. sativa endemicity in
Europe, prior to its transport by humans.
The previous three meta-analyses utilized pollen grain
morphology for pollen identification. Dörfler (1990) encoun-
tered problems separating Cannabis from Humulus pollen.
Many palynologists, confronted with the morphological sim-
ilarities between Cannabis and Humulus, resort to collective
names, e.g. Cannabis/Humulus, or Cannabaceae. Hereafter
we abbreviate these lumped data as C–H pollen. Clarke and
Merlin (2013) were flummoxed by FPSs that lumped data
as C–H pollen; they understood the complexities regarding
grain morphology (Fleming and Clarke 1998). Long etal.
(2017) resolved the C–H dilemma by limiting FPSs to stud-
ies that explicitly identified pollen as Cannabis—a strategy
that excluded a lot of C–H data.
Methods
Search strategy anddata analysis
We accessed a larger database by using several internet
search engines. The European Pollen Database (EPD, http://
www.europ eanpo llend ataba se.net) was searched in April
2013 (McPartland etal. 2013) and again in December 2015.
We retrieved fossil pollen studies that included pollen identi-
fied as Cannabis/Humulus, Humulus/Cannabis, Cannabis-
type, Humulus-type, or Cannabaceae. The FPSs deposited
in the EPD are typically linked to publications, but some
FPSs are unpublished “grey literature.” Additional FPSs
were identified via Web of Science, PubMed, and Google
Scholar. The keywords and Boolean operators were: palynol-
ogy AND (Cannabis OR Humulus). We also used citation
tracking—references in retrieved publications were searched
for antecedent sources, and these were retrieved.
We excluded FPSs that analysed strata limited to the his-
toric era, because those data did not inform our research
questions: the presence of pre-Neolithic endemicity, and the
identification of prehistoric hemp cultivators. To map pollen
in space and time, retrieved publications had to meet three
inclusion criteria: (1) precise geographical coordinates; (2)
accurate chronology; (3) a minimal amount of pollen grains.
1. Precise geographical coordinates were localized to
within a hundredth degree of latitude and longitude.
Some studies not provide geographical coordinates.
We obtained coordinates of those sites via Google
Earth, which uses the World Geodetic System of 1984
(WGS84) datum. The boundaries of our data collection
correspond to the definition of European territory by
Flora Europaea (Akeroyd 1993). The problematic east-
ern border of Europe is delimited by the crest of the
Greater Caucasus Mountains, the north western shore-
line of the Caspian Sea, the Ural River, and the crest of
the Ural Mountains.
2. Accurate chronology was achieved by restricting data
to FPSs with calibrated radiocarbon (14C) dates. Many
studies in the EPD have been retroactively calibrated,
using control points (relative and independent dates)
and CLAM software (Giesecke etal. 2014). A scar-
city of FPSs from the Pontic-Caspian steppe—a criti-
cal region—impelled us to include several uncalibrated
studies from that region. Possible dating errors arising
from retroactively calibrated data or from uncalibrated
data (as well as anomalously old 14C dates due to hard

637Vegetation History and Archaeobotany (2018) 27:635–648
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water effects) were minimized by our binning methodol-
ogy—temporal gaps of 500years were placed between
each time slice (see below).
3. Establishing the minimal amount of C–H pollen grains
as an inclusion criterion proved difficult. Palynolo-
gists debate the minimal amount of pollen required to
determine the presence of a plant species at a study site
(versus pollen that arrived there via long-distance trans-
port). The absolute minimum—one pollen grain—may
result in “utilization fallacy” (Fuller 2006). Wild-type C.
sativa colonizes ephemeral niches, such as flood water-
disturbed alluvial soil. This ephemeral niche is consist-
ent with its sporadic appearance in the fossil record. We
adopted a unique inclusion criterion: for a retrieved pub-
lication to be included in our study, C–H pollen had to
appear in a minimum of five strata within a stratigraphic
core. For an elaboration regarding the use of this metric,
please read Online Resource 1, Extended Methods.
Pollen identification
Palynologists usually identify Cannabis and Humulus pollen
by morphological characters, including grain diameter, exine
thickness, and pore protrusion or pore aperture diameter.
For example, Mercuri etal. (2002) identified grains ≤ 23µm
diameter as Humulus, ≥ 28µm as Cannabis, and between
23 and 28µm as undetermined. Others who tried to differ-
entiate Cannabis and Humulus by grain diameter, even in
comparison with reference slides, have considered it “most
unreliable” (Punt and Malotaux 1984), “not possible… a
suspect activity” (Whittington and Gordon 1987), “a dubi-
ous procedure” (Whittington and Edwards 1989), and “not
cleanly achieved” (Hauschild 1991). The use of exine thick-
ness, pore aperture diameter, and pore protrusion has also
been criticized and contested (Engelmark 1976; French and
Moore 1986; Whittington and Gordon 1987; Tweddle 2000).
Discerning Cannabis from Humulus is an old problem.
“The pollen in question consists of spherical, structure-
less, and almost completely transparent vesicles with thin
walls” (Fröman 1939). Purkyně (1830) provided the first
illustration of C. sativa pollen, but it was the sole species
whose identification he questioned, out of 284 species in
his book. This old problem remains intractable despite new
and improved microscopy. Simply: C. sativa and Humulus
lupulus are highly plastic yet homologous species, whose
morphological and phytochemical characters are variable
and overlap (McPartland and Guy 2017). Botanists have syn-
onymized H. lupulus under Cannabis (Scopoli 1772), and
herbarium specimens of C. sativa have been misidentified
as H. lupulus.
We collated 12 reference texts or methods papers, and
their data regarding mean grain diameters show great vari-
ability. For C. sativa they range from 19.0 to > 28µm, for
H. lupulus they range from 16.2 to < 25µm (see Online
Resource 1). Confronted with these inconsistencies, many
palynologists transform their identification into a larger
class, e.g. Cannabis/Humulus or Humulus/Cannabis. Or
they apply the collective names “Humulus-type,” “Can-
nabis-type”, or Cannabaceae (sic, which now includes
Celtidaceae).
To dissect these aggregate data, we used ecological prox-
ies as an inferential, probabilistic method to differentiate
Cannabis and Humulus pollen. Wild-type C. sativa flour-
ishes in steppes, an open, treeless habitat (de Candolle
1883; Herder 1892; Vavilov 1926). Temperate steppe is
dominated by Poaceae and Artemisia species. Desert steppe
is dominated by Artemisia spp. and Chenopodiaceae. Phy-
tosociologists and other field botanists report wild-type C.
sativa cohabitating with Poaceae, Artemisia, and Cheno-
podiaceae; hereafter abbreviated PAC (for attestations see
Online Resources 1).
Palynologists have extended these associations into the
past. The BIOME Project designates Cannabis fossil pollen
as a “botanical marker” of the “grassland biome”, along with
PAC pollen and the relative absence of tree pollen (Tara-
sov etal. 1998, 2000). Cannabis fossil pollen may indicate
a xerophytic steppe—hot and arid (van Geel etal. 2004;
Kuneš 2008) or a mesophytic steppe—moderately warm and
wet (Riehl and Pustovoytov 2006). “Dry tundra” describes
a Pleistocene-early Holocene biome that was cooler than
steppe, and drier than contemporary tundra. In this biome
assembly, Cannabis and Artemisia pollen are categorized
as “arctic forbs” (Binney etal. 2017) or cryophytes/xero-
phytes (Bolikhovskaya 2007). Dirksen and van Geel (2004)
commented, “The synchronous fluctuations of Artemisia,
Chenopodiaceae and Cannabis ruderalis pollen curves are
remarkable”.
In contrast, H. lupulus requires trees to climb. Wild H.
lupulus flourishes in mesophytic deciduous forests. Phytoso-
ciologists and other field botanists report H. lupulus associ-
ating with alder (Alnus spp.), willow (Salix spp.) and poplar
(Populus spp.), hereafter abbreviated ASP. Palynologists
have extended these associations into the past. Fries (1958,
1962) first noted synchrony in pollen counts of Humulus
and Alnus. He said C–H fossil pollen did not appear in Swe-
den until Alnus trees migrated into the region during the
early Holocene. BIOME project palynologists characterize
Humulus as a drought-intolerant climber of trees (Ni etal.
2010), and assign Humulus pollen as a botanical marker of
deciduous broadleaved forests (Zhou etal. 2007), or tropical
evergreen forests (Lee and Liew 2010).
Arboreal/nonarboreal ratio
Firbas (1937) reasoned that Neolithic humans had to clear
forests to grow crops. He detected this as a decrease in tree

638 Vegetation History and Archaeobotany (2018) 27:635–648
1 3
pollen (arboreal pollen, AP) and an increase in pollen of
grasses, sedges, and forbs (nonarboreal pollen, NAP). Some
palynologists argue that the AP-to-NAP ratio has limited
predictive value as an indicator of landscape openness.
Others find significant correlation between NAP percent-
ages and percentage cover of open herb vegetation. AP and
NAP percentages are oppositional—when one goes down,
the other goes up. Similarly, palynologists have shown that
Alnus and PAC demonstrate oppositional characters in stud-
ies using multivariate analyses, such as PCA, RDA, and NJ
methods.
Pollen ofcultivated C. sativa
Scholz (1957) distinguished between wild-type and culti-
vated Cannabis by grain diameter, 15–25µm and 25–35µm,
respectively. No palynologists have adopted grain diameter
as a criterion to distinguish between wild-type and cultivated
Cannabis. Many palynologists interpret C–H pollen as that
of cultivated hemp when its pollen count surges or becomes
a continuous curve in synchrony with pollen from other crop
plants (e.g. Fries 1958, 1962; Godwin 1967; Wilson 1975;
Maher 1977; van Zant etal. 1979; Whittington and Edwards
1989; Dörfler 1990; Peglar 1993; Hall etal. 1995; Fleming
and Clarke 1998).
The other crop plants in these studies include Avena
(oats), Hordeum (barley), Secale (rye), Triticum (wheat),
and Cerealia-type (undifferentiated cereal pollen). Pollen
curves of two weed species, Centaurea cyanus and Scleran-
thus annuus, have also been used to interpret C–H pollen as
that of cultivated hemp (Whittington and Jarvis 1986; Gail-
lard and Berglund 1988; Edwards and Whittington 1990).
An algorithm was developed to differentiate C–H pollen
(Fig.1). We interpreted C–H pollen as that of cultivated
Cannabis when it appeared de novo along with crop pol-
len, or increased at least twofold over earlier pre-Neolithic
counts. To differentiate C–H pollen in pre-agricultural
strata, we used ecological proxies. When C–H occurred
in a pollen assemblage where the AP-to-NAP ratio ≤ 2
(i.e. ≤ 33%/66%), dominated by steppe vegetation (PAC),
we interpreted it as wild-type Cannabis. When C–H
occurred in a pollen assemblage where the AP/NAP ratio
≥ 2 (i.e. ≥ 66%/33%), dominated by ASP, we inferred it to
be Humulus. In some ambiguous FPSs, pollen counts of
PAC and ASP rise and fall in near-synchrony, and the AP/
NAP ratio approaches 1:1 (i.e. 50%/50%). At these sites,
we classified C–H pollen as unresolved C/H.
Readers are invited to explore Online Resource 1 for:
(1) the morphological identification of Cannabis and
Humulus pollen; (2) phytosociological studies linking
C. sativa with PAC spp., and H. lupulus with ASP spp.;
(3) debates regarding AP/NAP ratios and pollen signals
indicative of crop cultivation; (4) methods of data extrac-
tion and binning for algorithm application.
Stratigraphical data were binned into six time slices,
with temporal gaps of 500years between each time slice,
to minimize errors from dating inaccuracies:
1. 18,500–15,000 cal bp, including the latter half of the
Last Glacial Maximum and the onset of deglaciation,
when dry tundra and steppe plants colonized northern
Europe, and mesophytic tree species were limited to gla-
cial refugia, mostly in southern peninsulas.
2. 14,500–10,500 cal bp, including the Late Glacial and
onset of the Holocene, an unstable period of deglacia-
tion, punctuated by short-lived warming and cooling
episodes, such as the Bølling, Older Dryas, Allerød, and
Younger Dryas.
3. 10,000–7,500 cal bp, including most of the Early Holo-
cene (Walker etal. 2012), a period of improved climate,
re-emerging forests, and increased anthropogenic impact
on landscapes, prior to Neolithic cultures penetrating
Europe beyond the Mediterranean coastline and the
lower reaches of the Danube River.
4. 7,000–5,000 cal bp, including most of the Middle Holo-
cene, a period including the Mid-Holocene Climatic
Optimum, when agriculture spread across much of low-
altitude Europe, and when copper smelting began.
5. 4,500–2,300 cal bp, onset of the Late Holocene, a period
that began with the Bronze age, spanned the Iron age,
and ended with the earliest recorded European history.
This period includes archaeological evidence of hemp
cultivation.
6. 2,000–800 cal bp, a period that began when Europe
beyond the Roman Empire was still in the prehistoric
Iron age. The period ends with the beginning of hop
cultivation. Our analysis stops there, in agreement with
Wilson (1975), who hypothesized that pollen from cul-
tivated hops may impact pollen diagrams (and thereby
Fig. 1 Algorithm for the identification of C–H pollen

639Vegetation History and Archaeobotany (2018) 27:635–648
1 3
conflict with part “B” of the pollen identification algo-
rithm).
GIS mapping
Latitude and longitude of each FPS was plotted, using geo-
graphic information system (GIS) software (ArcGIS 10.3).
FPS sites were plotted on six maps, corresponding to the
six binned time slices. Each FPS site was marked with a
symbol indicating pollen interpretation—either wild-type
C. sativa, cultivated C. sativa, H. lupulus, or unresolved
C/H pollen. To better illustrate data trends over time, the
six bins are grouped together as separate maps with the
same scale and extent (aka presented as small multiples).
Some authors of FPSs did not discuss the archaeological
contexts of their sites. The locations and time slices of FPSs
were compared with eight maps that delineated territories
of archaeological cultures: Early Neolithic (ca. 6800–3500
bce), Late Neolithic and Copper age (ca. 5500–2700 bce),
Early Bronze age (ca. 3200–1800 bce), Middle Bronze age
(ca. 3000–1500 bce), Late Bronze age (ca. 1700–500 bce),
Early Iron age (ca. 1100–400 bce), Middle-to-Late Iron
age (ca. 800 bce–100 ce), and End-stage Iron age cultures
beyond the Roman Empire (ca. 100–500 ce). These time
intervals overlapped because the Neolithic, Copper, Bronze,
and Iron ages spread at different rates across Europe. See
Online Resource 2 for maps and methodology.
Results
The search strategy identified 603 FPSs that included C–H
pollen from the Late Glacial/Holocene. Eighty studies
did not meet our inclusion criteria, and another 44 stud-
ies reported duplicate data. The remaining 479 FPSs were
tabulated, each with an accession number, study location,
details regarding application of the algorithm, and duplicate
reports. Excluded studies were also tabulated. Included and
excluded FPSs appear in Online Resource 3, TableS1 and
TableS2, respectively.
Geographical locations of FPSs, with pollen interpre-
tations, distributed over six times slices, are presented in
Figs.2, 3, 4, 5, 6, 7.Locations of allthe 479 FPSs, plotted on
a map of Europe, are provided in an interactive map, avail-
able at http://arcg.is/2jK9u Av (also see Online Resource 2,
Map S1, for a non-interactive version). Interactive function-
alities include FPS site queries (click on each individual
site to obtain its accession number and other data), pan and
zoom, and changing the basemap (for topography, vegeta-
tion type, etc.). Note that some FPSs are deep-water cores,
so they are located in the Black, Adriatic, and North Seas.
Data from the 479 FPSs were binned and mapped:
Bin 1 (18,500–15,000 cal bp, Fig.2). Only eleven FPSs
in this time slice reflect a paucity of pollen sediment during
the Late Glacial Maximum. In many areas of Europe, the
landscape was dominated by nonarboreal (NAP) pollen and
steppe species (PAC). The algorithm interprets C–H pollen
in this assemblage as wild-type Cannabis. However, pioneer
trees, especially Betula, occasionally blanketed landscapes
with up to 85% arboreal pollen (AP). C–H pollen in these
landscapes was interpreted as unresolved C/H pollen.
Bin 2 (14,500–10,500 cal bp, Fig.3). NAP, PAC, and C–H
pollen inferred as wild-type Cannabis occurred throughout
Europe. Pollen from all three Humulus associates—ASP—
began spreading from glacial refugia. At some FPS sites,
the percentage of ASP pollen equalled PAC pollen, which
made the determination of C–H pollen uncertain. At other
FPS sites, pollen counts of AP + ASP clearly overtook those
of NAP + PAC that dominated in Bin 1; C–H pollen at those
sites was interpreted as Humulus in forested landscapes.
Bin 3 (10,000–7,500 cal bp, Fig.4). More NAP-to-AP
turnover occurred, including many FPSs where PAC = ASP,
possibly representing the coexistence of H. lupulus and C.
sativa in forest-steppe communities. Crop plant pollen was
detected at several FPS sites, but these sites lacked C–H
pollen in this time slice.
Bin 4 (7,000–5,000 cal bp, Fig.5). AP + ASP expansion
peaked in this time slice, when C–H pollen interpreted as
Humulus blanketed Europe. Data consistent with wild-type
Cannabis pollen were limited to the Mediterranean coast
(Greece, Spain) and the Pontic steppe (Ukraine, Bulgaria).
FPS sites with crop pollen did not show signals interpreted
as cultivated Cannabis according to the algorithm, with one
exception (see discussion).
Bin 5 (4,500–2,300 cal bp, Fig.6). Humulus flourished
in heavily-forested Europe. Only 13 FPSs showed pollen
signals consistent with wild-type Cannabis. Thirty-five
FPSs showed C–H pollen interpreted as cultivated Canna-
bis, mostly north of the Alps.
Bin 6 (2,000–800 cal bp, Fig.7). The pollen signal of
Humulus was replaced by that of cultivated Cannabis
across Europe. Fourteen FPSs showed high levels of NAP,
PAC, and crop pollen, but no clear surge of C–H pollen.
This pollen signal is not addressed by the algorithm. It
may be interpreted as weedy C. sativa that escaped cultiva-
tion, or sampling sites that were too far away from cultiva-
tion sites to register a clear surge in pollen.
In addition to the above, we identified 36 FPSs with
C–H pollen that predated 18,500 cal bp. The studies are
few in number, and span a large swath of uncalibrated
time, from thousands (kya) to millions (mya) of years ago.
They were tabulated rather than mapped, in Table1.

640 Vegetation History and Archaeobotany (2018) 27:635–648
1 3
Discussion
This study has several limitations. As with any pollen-
based method, the algorithm (Fig.1) is challenged by
inherent assumptions and biases. It assumes that ecologi-
cal niches of modern Cannabis, Humulus, PAC, and ASP
can be extrapolated to past populations (the “nearest living
relative” paradigm). To wit, natural plant communities
break down in landscapes altered by anthropogenic activi-
ties. Synanthropic communities, however, often include
C. sativa and PAC species; we cite examples in Online
Resource 1. The results generated by our algorithm are
best characterized as “probabilities, not proofs.”
Fig. 2 Bin 1 (18,500–15,000 cal
bp). Background base map by
Natural Earth, free open-source
map data, http://www.natur alear
thdat a.com
Fig. 3 Bin 2 (14,500–10,500 cal
bp). Background base map by
Natural Earth, free open-source
map data, http://www.natur alear
thdat a.com

641Vegetation History and Archaeobotany (2018) 27:635–648
1 3
The dispersal of FPS datapoints in Figs.2, 3, 4, 5, 6
and 7 reflects the clumped distribution of palynologists,
not the distribution of pollen. Some regions of Europe
are dense with FPSs (e.g. UK, Switzerland, Czech Repub-
lic), whereas few studies have been conducted in Ukraine
and southeast Russia. The paucity of studies in southeast
Russia is unfortunate, because Flora Europaea states that
“native” populations grow there (Akeroyd 1993).
In Fig.7, copious pollen from cultivated Cannabis
no doubt swamped some of the signal coming from wild
Humulus. Conversely, woodland clearance would have
enhanced potential habitats for Humulus. Today, cultural
Fig. 4 Bin 3 (10,000–7,500 cal
bp). Background base map by
Natural Earth, free open-source
map data, http://www.natur alear
thdat a.com
Fig. 5 Bin 4 (7,000–5,000 cal
bp). Background base map by
Natural Earth, free open-source
map data, http://www.natur alear
thdat a.com

642 Vegetation History and Archaeobotany (2018) 27:635–648
1 3
landscapes provide artificial surfaces for wild Humulus
growth—forest edges, hedges, walls, and fences (Lisci and
Pacini 1993). These situations could result in a surge of
Humulus pollen, potentially misinterpreted as cultivated
Cannabis. See Online Resource 1 for elaborations on these
and other criticisms of our methods.
In general, when extracting data from FPSs, our dichot-
omizing proxies were quite robust: NAP vs. AP, and PAC
vs. ASP. This made the inference of C–H pollen as either
C. sativa or H. lupulus rather straightforward. Other
authors have noted that pollen counts of Alnus and PAC
demonstrate an oppositional character (Hicks and Birks
1996; Kuneš etal. 2008; Conner 2011).
Fig. 6 Bin 5 (4,500–2,300 cal
bp). Background base map by
Natural Earth, free open-source
map data, http://www.natur alear
thdat a.com
Fig. 7 Bin 6 (2,000–800 cal
bp). Background base map by
Natural Earth, free open-source
map data, http://www.natur alear
thdat a.com

643Vegetation History and Archaeobotany (2018) 27:635–648
1 3
Indigenous European C. sativa
Global studies of climate change indicate that climate vari-
ability began to cycle into stadials (glacial periods) and
interstadials (warm periods) during the Pliocene Epoch
(Ehlers and Gibbard 2007). The oldest C–H pollen consist-
ent with Cannabis in Europe appeared during the Olduvai
cold stage, beginning 1.8 mya (Danukalova 2010). Older
C–H pollen from the late Miocene, 6.1–5.3 mya (Ivanov
etal. 2007), appeared in an ambiguous milieu (AP/NAP
~ 1:1, PAC = ASP), which the algorithm classified as
unresolved C/H. However, another site in Bulgaria, also
from the late Miocene, reported a similar mixed flora—
and yielded a fossil fruit of Cannabis: carefully analysed,
illustrated, and convincing (Palamarev 1982).
Studies that predate 18,500 cal bp (Table1) and Bin 1
(18,500–15,000 cal bp, Fig.2) support our hypothesis that
Cannabis expanded from Asia to Europe prior to human
agency. This should not be surprising, because her sister
genus—Humulus—also expanded from Asia to Europe
prior to human agency. European print fossils of Humulus
date back to the Miocene (Collinson 1989). Several FPSs
in Fig.2 fall within regions traditionally considered glacial
refugia of tree species—in Iberia, Italy and Greece. Never-
theless, the pollen in these tree refugia was dominated by
NAP, PAC and C. sativa; they may represent “refugia within
refugia” (Feliner 2011).
It may seem like a climactic improbability that northern
Europe served as C. sativa habitat during the Last Glacial
Maximum (Fig.2) and subsequent deglaciation (Fig.3). But
recall, C. sativa has been classified an “arctic forb” (Bolik-
hovskaya 2007; Binney etal. 2017). In fact, C. sativa can
tolerate climatic conditions north of 68°N (Schübeler 1875).
In perspective, our maps here extend up to 63.5°N. Fur-
thermore, northern Europe underwent post-glacial isostatic
rebound. This caused land uplift, nearly 300m in places
(Berglund 2004). Uplift coupled with glacial melt created
alluvial ravines cutting through dry tundra and steppe—a
disturbed landscape perfect for C. sativa.
The dominance of NAP + PAC pollen in Bin 1 is gradu-
ally replaced by AP + ASP pollen in Bins 2 through 5. Thus
by proxy, C–H pollen interpreted as Cannabis in Bin 1 is
gradually replaced by Humulus in Bins 2 through 5. Our
estimates of PAC and ASP distribution and abundance
across time and space broadly agree with isopollen maps
by Huntley and Birks (1983). They present separate maps
of P, A, C, and A, S, P pollen across Europe, in time slices
corresponding to Bins 2 through 5, in a meta-analysis of
423 FPS. Our estimates also broadly agree with an updated
study by Brewer etal. (2017), who used pollen percentage
symbols for spatial visualization in a meta-analysis of 828
FPSs. Their maps show the distribution and abundance of
P, A, (no C), and A, S, P pollen. Our estimates of Alnus and
Salix expansion during the Holocene parallel results in other
studies (King and Ferris 1998; Alsos etal. 2009; Douda
etal. 2014). Also in agreement with our results, BIOME
studies show steppe landscapes contracting from 18 to 6kya,
and rebounding at 0kya (Prentice etal. 1996; Tarasov etal.
2000).
Aggregating many FPSs enables the separation of col-
lective signal from the noise within individual FPSs. A
trend emerges from the collective data: C. sativa colonized
Europe during stadials, and was largely replaced by H. lupu-
lus during interstadials. This trend parallels cycles reported
Table 1 Interpretation of C–H pollen in studies predating 18,500 cal bp
C–H pollen consistent with Cannabis sativa C–H pollen undeter-
mined (Cannabis–
Humulus)
C–H pollen consistent with Humulus lupulus
Last Glacial Maximum, OIS 4–2, 70–18.5 kya
Bulgaria (n = 2), Russia (2), Estonia, Greece, Ukraine
Weichselian cooling trend, OIS 5d-a, 115–70kya
Italy, Poland Poland, Ukraine
Eemian/Mikulino interglacial, OIS 5e, 130–115kya
Russia France, Italy, Netherlands, Poland (5), Russia, Sweden
Penultimate glaciation, OIS 6, 191–130kya
Russia (2), Italy
Zhizdra cooling event (OIS 7, 243–191kya), Sanian 2 glaciation (OIS 12, 420–400kya), or Gremyache interglacial (OIS 19, 770kya)
Poland (2), Russia (2)
Eopleistocene (1.8–1.2 mya) or Early Pliocene (5.32–3.6mya)
Russia, Romania, Kazakhstan
Late Miocene (11.6–5.8 mya) or Oligocene (33.9–23.0)
Bulgaria Russia, Georgia, Bulgaria, Italy, Czech Republic

644 Vegetation History and Archaeobotany (2018) 27:635–648
1 3
for Artemisia (Blyakharchuk and Amel’chenko 2012; Liu
etal. 2013; Cao etal. 2013). Thus C. sativa and Artemisia
retreated to “interstadial refugia” (sensu López-García etal.
2010), diametrically opposite to tree species, which retreated
to refugia during stadials.
Our study shows a nadir of C–H pollen interpreted as
Cannabis pollen in Bin 4 (Fig.5), following the Mid-Hol-
ocene Climatic Optimum (MHCO). Cannabis was limited
to two interstadial refugia: the Pontic steppe (Ukraine, Bul-
garia) and the Mediterranean coast (Greece, Spain). Aker-
oyd (1993) reports a single modern refugium of “native”
C. sativa persisting in the Pontic steppe (southeastern Rus-
sia). Consistent with our MHCO findings, Pokorný etal.
(2015) demonstrated that steppe landscapes underwent
a MHCO bottleneck in the Czech Republic. Their pollen
diagram showed Poaceae and Artemisia persisted through
the MHCO, but no Cannabis pollen appeared during that
interval. We hypothesize that this bottleneck contributed to
allopatric segregation between two recognized subspecies—
the European C. sativa ssp. sativa, and the Asian C. sativa
ssp. indica (Small and Cronquist 1976).
No cultivated C. sativa inNeolithic Europe
C–H pollen consistent with Cannabis largely disappeared
from Europe by the time farmers and/or agricultural technol-
ogy arrived from the Fertile Crescent. West Asian “founder
crops” diffused into Europe. This crop package included
flax, Linum usitatissimum L., a fiber and seed oil crop (func-
tionally analogous to C. sativa). We hypothesize that people
from three Neolithic cultures had the potential to domesti-
cate wild-type C. sativa. This hypothesis was generating by
constructing maps that delineated the territories of Neolithic
cultures (Online Resource 2, Maps S2, S3). We compared
these culture maps with locations of C–H pollen consistent
with wild-type Cannabis in Figs.4 and 5. Those locations
fell into the territories of Neolithic Greece, the Cardium
Pottery culture, and the Bug-Dniester culture. For schol-
ars interested in citations, see Online Resource 3, TableS1
(Neolithic Greece studies #89, 282, 284, 288, 289; Cardium
Pottery: #94, 196; Bug-Dniester culture: #237).
However, no pollen signals consistent with cultivated
Cannabis arise within these cultures, or any early Neolithic
cultures (e.g. Starčevo-Körös-Criş, Linearbandkeramik,
early Cucuteni-Tripolye, see Map S2). This agrees with
archaeological studies of these cultures, which lack evidence
of C. sativa (Cârciumaru 1996; Bogaard 2004; Kreuz etal.
2005; Conolly etal. 2008). When it comes to Cannabis,
these farmers either “missed the boat,” or their cultivation
of hemp was a “false start” (meaning its cultivation was
quickly abandoned).
Rimantienė (1979) identified Canabinaceae (sic) pol-
len at Šventoji in Lithuania, a Narva culture site with an
uncalibrated 14C date of 4,190 bp. She identified it as C.
sativa, alongside a grain of “millet” pollen. Our algorithm
interpreted the pollen as Humulus. Consistent with this,
Rimantienė (1992) stated that Alnus glutinosa surrounded
the Šventoji lagoon of 4,190 bp. We analysed 24 fossil pol-
len studies in the Baltic region (TableS1, studies #12–30,
246–250). All C–H pollen from the Baltic Neolithic was
interpreted as Humulus or C/H (undetermined). The earliest
C–H pollen suggestive of cultivated Cannabis in the Bal-
tic region appeared 500 bce (study #12). Piličiauskas etal.
(2017) recently deconstructed Rimantienė’s identification
of Cannabis and the entire concept of Subneolithic farming
in the Baltic region.
C. sativa duringtheCopper age
We compared the territories of Copper age cultures (Map
S3) with locations of C–H pollen consistent with Cannabis
in Fig.5. This suggests that two Copper age cultures had
the potential to domesticate wild-type C. sativa: the Greek
Chalcolithic (TableS1, studies #89, 94, 284, 288), and the
Cucuteni-Tripolye culture (study #237). C–H pollen consist-
ent with cultivated Cannabis occurred at one site in Bulgaria
(#274). This site may correspond to the Varna culture or
Gumelniţa culture. However, pollen at five other Varna and
Gumelniţa sites was interpreted as Humulus (#276), or unde-
termined C/H (#70, 71, 273, 275). Archaeological studies of
Gumelniţa and Cucuteni-Tripolye sites have found C. sativa
seeds and less-robust evidence—pottery seed impressions
(Clarke and Merlin 2013; Long etal. 2017; McPartland and
Hegman 2017).
C. sativa duringtheBronze age
Eight Bronze age cultures had potential: C–H pollen consist-
ent with wild-type Cannabis in Fig.6 appeared within the
boundaries of several Bronze age cultures (Maps S4–S6).
These include the Netted Ware culture (TableS1, study #6),
Ezero culture (#271), Yamnaya culture (#237, 427), Corded
Ware culture (#305), Bell-Beaker culture (#198), Terramara
culture (#347), Aegean Bronze age (#282, 284, 288), and
Mycenaean Greece (#282, 284, 288).
C–H pollen interpreted as cultivated C. sativa appeared in
four studies: One study in Yamnaya territory (#274) agrees
with archaeological studies, which have recovered C. sativa
seeds or pottery seed impressions (Clarke and Merlin 2013;
Long etal. 2017; McPartland and Hegman 2017). Two study
sites are associated with the Terramara culture (#344, 349).
However, pollen in 11 other studies at Terramara sites sug-
gested Humulus or indeterminate C/H pollen. One FPS in
France (#436) was likely contaminated by taphonomic pro-
cesses, as admitted by its authors.

645Vegetation History and Archaeobotany (2018) 27:635–648
1 3
Collectively, FPSs show evidence of hemp cultivation
during the Copper and Bronze ages. This poses a larger
question: was European C. sativa domesticated autochtho-
nously, separate from its domestication in eastern China?
This complex issue is discussed in our sister publication
(McPartland and Hegman 2017). Basically, we agree with
Vavilov (1926), “It is probable that the cultivation of hemp
arose simultaneously and independently in several places”.
C. sativa duringtheIron age
C–H pollen interpreted as cultivated Cannabis appeared
within territories and time slices occupied by several Iron
age cultures (Maps S7–S9). By the Iron age, the Proto-Indo-
European language diverged into several language groups.
We organized this section by language groups, including
Iranian, Greek, Celtic, Slavic, and Baltic languages.
The Iranian-speaking Scythians migrated to the Pontic
steppe from Central Asia. Three FPSs in Scythian territory
showed C–H pollen consistent with wild-type or cultivated
Cannabis (TableS1, studies #243, 244, 427). At the dawn
of European history (ca. 440 bce), Herodotus said
“grows both wild and cultivated” in the land of Scythia
(Herodotus 2007). No less than a dozen Scythian sites in
Europe have recovered seeds, pottery seed impressions,
cordage, or textiles (McPartland and Hegman 2017).
Herodotus introduced with “there is, there
exists”, a verb he joined to a noun he assumed was unknown
to the reader. Pollen suggestive of wild-type Cannabis
occurred in Greece prior to Herodotus’ time, but no archae-
ological evidence suggests the Iron age Greeks recognized
its utility. After Herodotus’ time, pollen consistent with
cultivated Cannabis appeared in Greece or Greek colonies
(studies #84, 361, 362). Pollen consistent with cultivated
Cannabis appeared at one FPS site prior to Herodotus, ca.
525 bce (#287). However, that site borders Thrace. Herodo-
tus described the Thracians making textiles from
fiber. Surprisingly, no other studies within Thracian territory
showed pollen signals of cultivated C. sativa in the bce era.
The Iron age Celts (Hallstatt phases C and D, and La
Tène culture) grew hemp, as attested by plentiful macro-
scopic evidence (Clarke and Merlin 2013; Long etal. 2017;
McPartland and Hegman 2017). C–H pollen consistent with
cultivated Cannabis was found in France (#184, 189, 190,
191, 193, 366, 369, 371–374, 380, 436), Germany (#126,
128, 130, 132, 134, 135), Switzerland (#334, 336, 442, 443),
Great Britain (#201, 390), Hungary (#95, 97), Czech Repub-
lic (#114, 451), northern Italy (#340), and Spain (#386).
This plethora of evidence partially reflects the density of
palynologists in these countries.
Studies in Proto-Slavic territories showed pollen sig-
nals consistent with hemp cultivation, associated with
the Pomeranian culture (#43, 45, 265), Przeworsk culture
(#38, 39, 44, 47, 48, 51, 262, 263, 266), and Zarubintsy
culture (#239). Three Proto-Baltic cultures also showed
C–H pollen consistent with cultivated Cannabis: the West
Baltic Barrow Culture (#12, 13, 28, 256, 474), Milograd
culture (#245), and Bogaczewo culture (#12, 13, 16, 28,
253, 256). Proto-Germanic cultures showed evidence of
hemp cultivation: the Jastorf culture (#317), Nordic Pre-
Roman Iron age (#230), and Nordic Roman Iron age (#232,
233, 299, 397, 457), as well as the Proto-Germanic-Slavic
Wielbark culture (#34, 259, 260).
The question arises whether Celtic, Proto-Slavic, and
Proto-Baltic cultures began cultivating C. sativa autoch-
thonously, or as a result of interacting with Scythians.
The evidence of Scythian cultivation is old. In Central
Asia, Cannabis pollen at Proto-Scythian Tagar culture
sites arises 900 bce (McPartland and Guy 2016). After
900 bce the Scythians moved to the Pontic steppe, where
signals of hemp cultivation preceded their arrival, back to
the Bronze age.
The Scythians impacted deeply on the Celts, in the realms
of art, animal husbandry, military strategy, language, and
even clothing. The oldest evidence of Scythian–Celtic inter-
actions that we could find was a 7th century bce burial in
Bulgaria, which combined elements of Scythian culture
along with a Hallstatt vessel (Braund 2015). Scythian arti-
facts in Hallstatt-occupied Hungary first appear around 550
bce (Bartosiewicz and Gál 2010). A Hallstatt burial at Vix
in France from 525 bce contains items and motifs inspired
by Scythian culture (Megaw 1966).
These data collectively suggest a conservative date of 550
bce as the terminus post quem for Scythian contact with the
Celts. Only three sites in Celtic territory showed pollen sig-
nals consistent with hemp cultivation prior to 550 bce (#114,
135, 340). To wit, the oldest ones (#135, 340) had problems
with dating. In contrast, 28 FPSs in Celtic territory showed
pollen signals of hemp cultivation arising post-550 bce, after
their contact with the Scythians.
The Scythians also impacted Proto-Slavic cultures. The
Scythians left a trail of burned-out settlements built by the
Proto-Slavic Lusatian culture around 600 bce (Bukowski
1977). A horde of Scythian artifacts found at Witaszkowo
in Lusatia dates to 550 bce (Furtwängler 1883). Only two
pre-550 bce sites in Slavic/Baltic territory showed signals
consistent with hemp cultivation, and they occurred in the
southeast, towards the Scythian homeland (#245, 580 bce;
#265, 570 bce). Ralska-Jasiewiczowa and van Geel (1998)
linked the appearance of Cannabis pollen in Poland with
Scythian incursions. The Scythians appear to be responsible
for the spread of Cannabis amongst several Iron age Euro-
pean cultures.
Moving into Bin 6 (Fig.7), C–H pollen interpreted as cul-
tivated Cannabis blankets much of Europe. Dörfler (1990)
cites macroscopic and pollen findings of hemp cultivation

646 Vegetation History and Archaeobotany (2018) 27:635–648
1 3
spreading into new regions in synchrony with Roman
invasions.
Pollen evidence suggestive of hemp cultivation appears in
new places after the Romans arrived (Map S9), such as the
Italian Alps (#171, 173, 174), Spain (#197, 386), Switzer-
land (#169), Austria (#309), Great Britain (#201, 203, 207),
and Greece (#282, 286).
We plan to compare these results with linguistic data, by
examining European cognates for hemp in Indo-European,
Finno-Ugric, Caucasus, and Semitic language families. We
also plan to extend our fossil pollen research into Asia.
Acknowledgements Felix Bittmann, Anna Maria Mercuri, Mark Mer-
lin, and two anonymous reviewers greatly improved this manuscript
with their suggestions. Funding was provided by GW Pharmaceuticals.
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