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Did Indo-European Languages Spread Before Farming?
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
The last 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 of languages.

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
An 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?
The 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 of farmers.

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 views.

Table 1. Sudden large climate changes and stable climate phases in Europe/Near East during the last 15,000 calendar years, from Adams (1998).
Sources 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 deglaciation begins.

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 than today's

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 than today's.

(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) in many areas

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Jonathan Adams
MS 6335, Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA

Marcel Otte
Université de Liège, Service de Préhistoire, place du XX Août 7, Bâtiment A1, 4000 Liège, Belgium