Did Indo-European Languages Spread
by Jonathan Adams and Marcel Otten
The late Glacial record of vegetation and climate suggests that
major changes in hunter-gatherer population density might have
occurred across Europe and Asia as a result of extreme climate
fluctuations. We hypothesise that a reduction in population
density across most of the region during the coldest part of
the Younger Dryas (around 12,800-11,400 cal. y.a.) may have
been followed by a sudden rebound phase, when climate switched
back to warm, moist Holocene conditions over only a few decades.
A 'sparse wave' of hunter-gatherers migrating rapidly out of
a refugial area (possibly located in southern Europe and/or
the Near East) would have made a disproportionate contribution
to the genetic and linguistic legacy of the region. This may
explain part of the initial prehistoric dispersal pattern of
the Indo-European languages. Other smaller and somewhat later
climate changes, such as the cold event at 8,200 cal. y.a.,
are also candidates for this process of regional depopulation
followed by repopulation from a restricted source region. The
possibility should be considered in addition to hypotheses invoking
spread of these languages by early farmers or warlike cultures.
The question of how Indo-European family of languages came to
occupy a broad swathe of Europe and western Asia has long attracted
discussion. The actual range that the Indo-European family of
languages had achieved by early historical times is uncertain,
but they were certainly present in central and northern Europe,
southeastern Europe, Anatolia and parts of the Near and Middle
East. Celtic, Germanic and Slavic migrations may have provided
a relatively late overlay of Indo-European languages in parts
of western and northern Europe, though without written records
of the pre-existing languages it is impossible to say what what
widespread before then. Migrations and conquest may likewise
have carried Sanskrit and Tocharian further eastwards shortly
before early historical times. While acknowledging that these
identifiable movements of cultures and peoples contributed to
the later spread of the Indo-European languages, scholars have
long discussed what events before this time might have led to
this group being present widely through central, northern, south-eastern
Europe and the Near and MIddle East.
Recent discussion of the prehistoric spreading of the Indo-European
language group has generally concentrated on two alternative
sets of hypotheses. On one hand there is the view that migrations
of war-like cultures (e.g. the 'Kurgan' or 'Battle-Axe' Culture)
(Childe 1950, Gimbutas 1980) had spread the languages out from
a common point of origin through conquest of relatively passive
farming populations. A more recent alternative view (Renfrew
1987, 1992) is that the main event in the spread of the Western
Branch of these languages was the initial spread of farming
out of the Near East, providing a population 'wave' (due the
increased carrying capacity of the farming lifeway) that swamped
out the languages of hunter-gatherer groups, speaking non-Indo
European languages, that had previously existed in the area.
This idea has received some support from genetic evidence of
a south-east to north-west gradient in gene marker frequencies
across Europe (Cavalli-Sforza et al. 1994.), which has been
taken to be the legacy of the 'farming wave' that spread out
of Anatolia beginning around 9,000 BP. The genetic evidence
from the 'farming wave' has been disputed however, on the grounds
that other (earlier or later) population movements could have
followed the same track.
While both the 'Battle-Axe' and the 'Farming Wave' hypotheses
have much to merit them, it is important to bear in mind that
they may not be the only reasonable explanations in terms of
what is known of the pre-history of Europe and western Asia,
against a background of emvironmental changes. The possibility
that the initial dispersal event of the Indo-European languages
involved not neolithic farmers nor bronze-age warriors, but
mesolithic hunter-gatherers has been mentioned briefly by several
authors (e.g. Renfrew 1987). However, none seems to have given
the idea more than a passing thought. Here we aim to discuss
this idea in greater depth, examaining what is known of the
climate record and the archaeological record, together with
general ecological principles of populations, to determine whether
this hypothesis stands up to more detailed analysis.
How languages may spread due
to climate instability
100,000 years have been marked by large numbers of dramatic
climate oscillations (van Andel & Tzedakis 1996), each of
which would have been capable of causing changes in human population
density as the resource base shifted. Episodes of relatively
low population density, for example during intense cold and
dry phases, would have been followed by rebound periods in which
humans could expand in range and in numbers across the region.
As well as acting as a source of genetic shifts in population
composition, the 'sampling error' caused by contraction of populations,
followed by exponential expansion of populations out from refuge
areas, could tend to provide waves of linguistic and cultural
uniformity to spread across the region. Just such a wave of
population out of the Near East may have carried Indo-European
languages across much of Europe and part of the way eastward
into central Asia.
Following a climate phase marked by low human population densities
across the region, any one group that acquired both the general
cultural traits that caused it to spread rapidly out of a refugium,
and the technology to enable it to do so, would have experienced
rapid exponential population growth in an environment relatively
free from competition by other hunter-gatherer groups. Such
a group, spreading out northwards and westwards, and possibly
eastwards as well, would make a disproportionate contribution
to the genetic and linguistic legacy of Europe and parts of
the Near East.
Other groups even a few centuries slower in expanding their
range and populations in tune with the climate change would
have become numerically dominated by the earlier colonists as
they left their refugial homelands, given the likely exponential
growth rate of each population. Even at the relatively low densities
that hunter-gatherer populations would have been capable of
achieving, competition or at least interaction between groups
would eventually have become more frequent, with less abundant
(non- Indo-European speaking) groups much more likely to lose
their cultural and linguistic identity among a larger wave of
Indo-European speakers. This scenario, of separate refugial
populations which failed to expand fast enough to dominate linguistically,
may explain the existence of the Basque language group, as a
'potential' European dominant that narrowly failed to expand
out before the Indo-European speakers became abundant in central
and eastern Europe, south-eastern Europe and possibly also most
other parts of Europe. The extinct Etruscan, Ligurian and Iberian
language groups may be regarded a further examples of the same.
As the hypothetical Indo-European wave spread out in each direction,
it can be expected to have 'gathered up' the genetic and linguistic
legacy of scattered smaller populations it encountered along
its way, as each of these began a slightly later spread out
of southern European refugia. This process of 'gathering up'
may explain some of the current east-west and north-south genetic
gradients which now exist in Europe, and some of the differences
between the present-day branches of the Indo-European family
It is thus possible that much of the initial (mid-Holocene)
range of the Indo-European languages across central and northern
Europe, the Balkans and the Near East was achieved by the rapid
spread of a 'sparse wave' of hunter-gatherers, out of either
southern Europe, the Levant, Anatolia or western Asia, preceding
the 'farming wave'.
The potential importance of the
Younger Dryas cold phase
obvious candidate for an environmental change which could result
in rapid and widespread change in languages, cultures and genetic
composition of human populations is the Younger Dryas cold event
(about 10,800-10,000 14C years ago) which returned much of western
Asia to cold semi-desert conditions (Huntley & Birks 1983,
Starkel 1991, Landmann et al. 1996, Rossignol-Strick and Planchais
1992, Velichko 1993), apparently through a series of rapid stepwise
cooling events. The transition to the Holocene is marked by
noticable changes in technologies (to the Mesolithic) and in
human skeletal morphology across this region, possibly suggesting
an immigration event. Reviewing the evidence for different hunter-gatherer
carrying capacities in different environments, Steele et al.
(1998) suggest that temperate forest and moist steppe have a
much higher overall carrying capacity than either semi-desert
or arctic environments.
Based on a range of different sources of environmental evidence,
Rossignol-Strick (1995) suggests that in many areas of Greece
and across Turkey, the Younger Dryas period was even more arid
than the most extreme part of the last glacial, with semi-desert
predominant. Conditions across most of the rest of Europe are
variously thought to have resembled open dry forest steppe or
possibly (at some stages) semi-desert (Starkel 1991). A priori,
such conditions may be expected to have resulted in some change
in human population densities and distribution, though it is
difficult to demonstrate or disprove this idea, given the limitations
in the archaeological record for the Younger Dryas period. In
Europe and most of the Near East the record of human occupation
during the Younger Dryas is ambiguous, with the 'age plateau'
in radiocarbon ages adding to the confusion (10,000 years ago
in radiocarbon terms can mean anything between 11,200 to 12,200
'real' years ago). In northern and central Europe, the record
is perhaps detailed enough to suggest a complete or almost complete
depopulation during the Younger Dryas. However, in the Levant
conditions seem to have remained relatively moist (Rossignol-Strick
1995), with relatively strong signs of continuity in human settlement
(the Natufian) (Henry 1989). Even in this area, for instance
in the Jordan Valley, aridity and a large decrease in food plants
are accompanied by more restricted human populations clustered
around relatively moist 'oases' (Wright 1993). Following the
Younger Dryas, warm, moist Holocene conditions seem to have
returned rapidly all across Europe and western Asia, taking
only a few decades according to the latest ice core indicators
of regional climate (Taylor et al. 1997). Given the magnitude
of the change in environments across the region, the earlier
rapid climate transition (about 12,000 14C y.a., or 14,500 ca.
y.a.) into the much colder, arid Younger Dryas could well have
eliminated much of the previous late Palaeolithic population
of northern and central Europe, or at least drastically reduced
inland population densities, and (from available indications
of the carrying capacity of temperate forest environments for
hunter-gatherers: Steele et al. 1998) the rapid return of warm
conditions would have provided an opportunity for rapid human
population expansion to fill this gap.
If one takes Renfrew's view that such dating is unreliable,
then an earlier divergence relating to hunter-gatherer recolonization
after the Younger Dryas may be more plausible for a spread of
Indo-European languages by this type of mechanism (this is especially
so considering the large amplitude and very sudden nature of
this event). Renfrew (1987, 1992) has vigorously attacked the
techniques of linguistic dating and has found broad support
among archaeologists, if not among linguists. He makes the point
that linguistic dating (based on degree of similarity in vocabulary,
and the use of specific 'technology' words to pin down the culture
of the earliest Indo-Europeans) is in itself potentially subject
to great imprecision.
Around a factor of two error in the estimate of rate of divergence,
taken from the earliest written records, would be sufficient
to push the point of common origin back several thousand years
from the early-to-mid Holocene to the earliest Holocene. Given
that during this time there has been a drastic cultural change,
to relatively sedentary Neolithic farming (in addition with
lesser cultural changes in trade patterns and technology), all
across the region and one must ask whether the linguistic chronology
is accurate across such a change in group size, inter-group
interaction and cultural complexity. One can suggest that for
instance (M. Fraser pers. comm.) relatively mobile hunter-gatherer
populations moving across large distances of the European continent
would have retained their cultural and linguistic unity more
readily than denser and more sedentary farming populations.
We do not claim that this particular hypothesis has any more
to merit it than either the 'battle-ax' hypothesis or the 'farming
wave' hypothesis, merely that it should be seriously considered
(given the uncertainty over the early linguistic history of
the region) alongside these as another possible scenario. Further
light might be shed on this matter if and when the archaeological
record of the region improves, allowing this hypothesis to be
subject to more rigorous testing. For example, good evidence
of a strong depopulation of most of Europe and western Asia
during all or part of the Younger Dryas or the early Holocene
cold phase would lend support to it, while lack of any depopulation
may be seen as evidence against this.
A plethora of population waves
in the Late Glacial and Holocene?
post-Younger Dryas colonization hypothesis is only one of a
range of potential scenarios, suggested by the paleoenvironmental
and archaeological record, leading to the spread of Indo-European
languages, or higher-order language groups such as the paired
Indo-European/Uralic familes, or the still broader and more
heterogenous Nostratic superfamily.
Another similar candidate event that might have affected the
spread of IE by either hunter-gatherers or early farmers (or
both) is the widespread cold, dry event at 8,200 cal. y.a. (Table
1.). This event seems to have been about half-way as severe
as the Younger Dryas (Adams et al. 1998), to have come on (and
also ended) over at most a few decades, lasting in total about
200 years. Here again, a decline in human population densities
across much of the region seems plausible from the extent and
the sudden-ness of this event. Turnover in population or in
cultural identity among hunter-gatherers resulting from this
disruption might well have initiated or added to the spread
of the Indo-European languages.
Estimates of the linguistic chronology of the Indo-European
languages have been used to suggest that much of their common
vocabulary has a more recent origin (about 7,000 years ago)
(Swadesh 1972) than the early Holocene divergence that this
'sparse wave' hypothesis (and Renfrew's 'farming wave' hypothesis)
would seem to require (about 10,000-11,000 years ago). In this
sense, the more likely candidate is the later, less severe cold
event 8,200 years ago.
It is also necessary to bear in mind the possibility (though
it conflicts still more strongly with the linguistic dating)
that the population increase causing the initial phase of spread
the Indo-European languages occurred at the earlier warming
event at the end of the Last Glacial Maximum (about 14,500 'calendar'
years ago), with the onset of the Younger Dryas itself, or perhaps
even earlier events (Otte 1994). One can also envisage a range
of scenarios combining aspects of the three hypotheses (the
'battle-axe, the 'farming wave' hypotheses, and the 'sparse
wave' idea presented here). Quite independent of climate change,
a more effective 'Mesolithic' technology might directly have
lead to a population 'wave' of increased carrying capacity analagous
to that associated with the Neolithic transition. As pointed
out above, another major cold and arid event - lasting perhaps
200 years - affected Europe and western Asia around 7,400 14C
y.a./8,000 cal. y.a. (Alley et al. 1997) (Table 1.).
At different stages all three processes ('sparse wave', 'farming
wave' and 'battle-axe migrations') might coincidentally have
tended to spread the Indo-European language group. An initial
early Holocene 'sparse wave' spread of the Indo-European languages
may have been followed by a period of relatively long-distance
cultural and linguistic exchange (with possible spreading of
innovations in the language, continually 'updating' aspects
of the general substratum of Indo-European languages; sensu
Sherratt 1996) by relatively mobile hunter-gatherer groups,
and later farming and warrior groups.
A major refuge of population in the Europe-west Asian region
during the Younger Dryas seems to have been the general area
around the Jordan Valley, where populations clustered in moist
sites where wild nuts and grains could be gathered. It is interesting
to consider that this region, having the general characteristics
of a source region for a 'sparse wave' of hunter gatherers,
was also a key source for the 'farming wave' of Neolithic farmers.
The Indo-European Languages might thus have been propelled out
of this source region by two successive population waves, first
the faster wave of hunter-gatherers, and then a slower wave
The idea that a phase of colder, dryer conditions might have
led to a regional decline in population density depends crucially
on the cultural habits and cultural flexibility of the hunter-gatherer
inhabitants of the region. One might hypothesise (as mentioned
above) that an opening-up of the returning woodlands due to
cold and/or aridity would have favoured hunting of large animals,
enabling an increase in population density. This could merely
push the dating of the necessary population wave slightly further
back in time. However, animal protien is not a principal source
of food outside arctic and coastal environments, so it would
be unlikely to result in anything other than a net decrease
in population elsewhere as the plant food availability from
wild grasses and nut-bearing trees declined with a shift towards
cold steppe and semi-desert conditions. The upshot of the complexity
of human behaviours is that different cultural groups of humans
might have responded to the same change in opposite ways, and
such a pattern of simultaneous decline of one group and expansion
of another may produce a pattern of linguistic spread. In any
caser, overall population density seems likely to have declined
during cold, arid events and the archaeological evidence from
the Near East supports this.
Thus, if climate events were fast and intense enough to significantly
disrupt hunter-gatherer (and/or farming) populations, they may
have been responsible for population or cultural replacements
which helped to spread languages. Since the most intense events
(the Younger Dryas and the 8,200 y.a. cold event) precede the
Neolithic across most of the Europe/Near East region, hunter
gatherers may have been the vectors of the Indo-European languages.
This is merely speculation, but it is necessary to set out
the range of possible scenarios in order to show that the situation
in the region could well be more complex than has generally
been thought. From considering the very variable environmental
record of the Late Glacial and Holocene, it seems that there
would have been ample opportunities for population and cultural/linguistic
replacement quite unrelated to agriculture or migrations of
warriors on horseback.
The paleoenvironmental record suggests various times
over the last 15,000 years at which major changes in hunter-gatherer
population density could have occurred on a regional scale,
due to environmental changes. Such population shifts would be
difficult to detect in a sparse archaeological record subject
to large 14C anomalies, but they remain a distinct possibility
given the magnitude of the climate and ecological changes recorded
from across the region. While the ending of the Younger Dryas
event seems particularly likely to have resulted in population
waves spreading across the region within the approximate time
range of the origin of Indo-European languages, any one of these
prehistoric changes could have initiated the spread of the Indo-European
language group (and in a broader sense the linked Indo-European/Finno-Ugric
group). Given the existing dating and the detailed linguistic
analysis which suggests a divergence time around 7,000 cal.
y.a., a somewhat later climate change (early-to-mid Holocene;
e.g. the 8,200 cal. y.a. or the 5,900 cal. y.a. cold events;
Table 1.) would seem to rest more easily with observations.
An 8,200 y.a. change could have promoted spread of Indo-European
languages by either hunter gatherers, farmers, or both.
Alternatively, climate change might have had little or no role
in the actual spreading of the languages, by farmers or post-neolithic
warriors. Different processes could coincidentally have aided
the spread of the Indo-European language family at different
times. It may be that an initial 'sparse wave' of recolonizing
hunter-gatherers carried this group of languages part-way into
central Europe and western Asia, with later processes such as
the spread of farming and migrations of warrior cultures having
resulted in a further net spreading of this group of languages.
The purpose of the paper has been to advocate and discuss a
fairly speculative hypothesis (that climate change promoted
spread of IE languages by causing changes in population density
of hunter-gatherer groups) which may be difficult or impossible
to test. Given the a priori case which can be made, this 'sparse
wave' hypothesis seems fairly plausible, although like the 'farming
wave' hypothesis of Renfrew the contradictions with paleolinguistic
analyses can be seen as a weakness. The severity of this weakness
is uncertain, however, as Renfrew (1987, 1992) has pointed out
various grounds on which paleolinguistics can be doubted.
The general hypothesis that past climate changes strongly affected
linguistic patterns can also merge into more traditional explanations;
sudden climate change could have been the primary cause of migrations
of IE-speaking neolithic farmers or horse-riding warriors. If
one accepts th paleolinguistic view that such 'technology' words
as 'wheel' and 'copper' were initially present at the point
of divergence of Indo-European languages, and that they actually
applied to technology items such as a fully-formed wheel or
worked copper, then the 8,200 y.a. or the 5,900 y.a. climate
events (rather than the Younger Dryas) could have been more
important, respectively influencing migrations of farming groups
or of horse-riding warriors.
Thus we must conclude on a rather defeatist note: the fact
that one can so readily add and interchange alternative hypotheses
concerning the spread of the Indo-European languages (and other
language groups, all of which have formed in the highly variable
world of the Late Quaternary period) should perhaps be seen
as reason for scepticism regarding any prospect of understanding
the true nature of the initial process of spread of the Indo-European
languages. Nevertheless 'finding out what one does not know'
is a vital part of the scientific process; it is always better
to realise that there are grounds for uncertainty than to hold
an unfounded belief that one knows the answer. This uncertainty
gives reason for open-mindedness as to the true causes of the
spread of IE, rather than any sharp division into entrenched
Table 1. Sudden large climate
changes and stable climate phases in Europe/Near East during
the last 15,000 calendar years, from Adams (1998).
of evidence include pollen, animal fossils, marine, lake and
ice cores, and general sedimentology. It is generally thought
likely that many or most of these changes occurred on a timescale
of several decades or less (Adams et al. 1998).
14,500 y.a. - rapid warming and moistening of climates. Rapid
13,500 y.a. - Climates at least as warm and moist as today's
13,000 y.a. 'Older Dryas' cold phase (lasting about 200 years)
before a partial return to warmer conditions.
12,800 y.a. (+/- 200 years)- rapid stepwise onset of the cold,
dry Younger Dryas.
11,500 y.a. (+/- 200 years) - Younger Dryas ends suddenly over
a few decades, back to warmth and moist climates (Holocene,
or Isotope Stage 1)
9,000 y.a. - 8,200 y.a. - climates warmer and often moister
about 8,200 y.a. - sudden cool and dry phase lasting about
200 years, about half-way as severe as the Younger Dryas.
8,000-4,500 y.a. - climates generally slightly warmer and moister
(but; at 5,900 y.a. - a possible sudden and short-lived cold
phase corresponding to the 'elm decline').
Since about 4,500 y.a. - climates fairly similar to the present
2,600 y.a. - relatively wet/cold event (of unknown duration)
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MS 6335, Environmental Sciences Division, Oak
Ridge National Laboratory, Oak Ridge, TN 37831, USA
Université de Liège, Service de Préhistoire,
place du XX Août 7, Bâtiment A1, 4000 Liège,