Climate and Prehistoric Migration

[Tautalus]

This paper examines one of the central questions of human history: what determined migration before states, borders, and modern economies existed? The paper argues that prehistoric migration was shaped primarily by ecology. People moved toward environments where their existing knowledge of farming, herding, or foraging remained useful. Climate, rainfall, and soil conditions therefore acted as powerful constraints on mobility across Eurasia over the last 10,000 years.

The paper introduces the idea of “ecological sorting”. Human populations accumulated highly localised environmental knowledge. Farmers understood specific growing seasons, soils, and crop cycles, pastoralists understood grazing systems and rainfall patterns, foragers relied on detailed landscape knowledge tied to animal routes, plant resources, and seasonal cycles. This knowledge functioned as a form of human capital that lost value when populations moved into very different ecological settings. Migration was therefore more likely between regions with similar climates and environmental conditions.

To test this theory, the authors use ancient DNA from more than 7,000 prehistoric individuals across Western Eurasia. They used identity-by-descent (IBD) DNA segments. When two ancient individuals share long DNA segments, they inherited them from a relatively recent common ancestor. If those individuals are buried far apart, migration must have occurred somewhere within their lineage. By aggregating thousands of these genetic connections, the paper reconstructs large-scale prehistoric migration flows.

The findings reveal extraordinary levels of prehistoric mobility. Among genetically related individuals, the average separation distance was approximately 1,550 kilometres. Some movements were far greater. One of the clearest examples involves the Yamnaya culture of the Pontic-Caspian steppe. A single Yamnaya individual buried near Samara around 3200 BCE had genetically identifiable descendants both 2,600 kilometres east in southern Siberia and more than 2,200 kilometres west in Central Europe only a few centuries later. The eastern branch is associated with the Afanasievo expansion, while the western branch connects to the Corded Ware culture horizon. The paper presents this case as direct evidence for the massive Bronze Age steppe migrations that reshaped Eurasian populations.

The authors demonstrate that migration declined sharply as ecological differences increased. Differences in growing degree days, rainfall, and soils all significantly reduced migration flows. People consistently moved toward environments resembling those of their homelands. This effect remained strong even after accounting for geographic distance, mountains, rivers, and travel difficulty.

The study also shows that different subsistence systems responded to different environmental pressures. Farming populations matched most strongly on temperature and soils because agriculture depended heavily on growing seasons and land quality. Pastoralist populations matched most strongly on precipitation because grazing systems depended on grassland productivity and moisture availability.

These patterns are directly linked to specific archaeological cultures. Early farming societies, especially the Linear Pottery culture culture, expanded during warm periods associated with the Holocene Climatic Optimum. The paper argues that warming expanded the range of cereal agriculture across Europe and enabled the Neolithic spread of farming into Central Europe. LBK populations also show strong matching to fertile loess soils, illustrating how ecological constraints shaped the spread of agriculture.

By contrast, steppe pastoralist groups such as the Yamnaya, Sintashta, and later Scythian related populations expanded during periods of climatic cooling after 3000 BCE. Cooling increased the extent of grassland ecosystems favourable to herding economies. The paper associates the rapid increase in migration speed after 3000 BCE with technological innovations such as wagons, horseback riding, dairying, and the broader Secondary Products Revolution.

The Corded Ware culture expansion is interpreted as part of this broader steppe mobility system. The paper uses ancient DNA to show that Corded Ware populations carried ancestry directly connected to Yamnaya individuals from the Pontic steppe. These migrations unfolded along east-west ecological corridors where climates remained relatively similar across Eurasia. The authors connect this pattern to the long standing argument that Eurasia’s east-west orientation facilitated large scale agricultural and pastoral diffusion because climates remained more consistent across latitude bands.

The paper also discusses the broader westward Bronze Age expansions associated with the Bell Beaker culture phenomenon. Although Bell Beaker populations are less discussed than Yamnaya or Corded Ware groups, they are interpreted within the same system of ecological and demographic expansion that reshaped Europe during the Bronze Age.

Another major contribution of the study is its argument that migration functioned as a mechanism of climate adaptation. Populations experiencing warming tended to relocate toward cooler destinations, while populations experiencing cooling moved toward warmer ones. On average, migration offset around 40% of local temperature change. The authors therefore present migration as a long-run adaptive response to environmental stress rather than merely a product of conflict or demographic pressure.

Finally, the paper argues that migration reshaped environments themselves. Using fossil pollen data, the authors show that destinations receiving large numbers of migrants gradually developed vegetation patterns similar to those of the migrants’ homelands. Farming migrants increased cereal cultivation and transformed landscapes through deforestation and agriculture, while pastoral migrants altered grassland-forest balances through grazing systems. Migration therefore not only responded to ecological conditions but also transformed ecosystems across Eurasia.

Overall, the paper presents a unified explanation of prehistoric migration in which climate, ecology, and subsistence technology structured the movement of populations over millennia. Warming periods favoured agricultural expansion by early farming cultures such as the LBK, while cooling periods favoured steppe pastoral expansions associated with Yamnaya and related groups. Ancient DNA allows the authors to reconstruct these movements quantitatively, offering one of the most detailed pictures yet of how climate shaped the human past.
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Abstract

What factors drove human migration before modern states, markets, and borders? We develop a framework of ecological sorting in which climate-specific subsistence knowledge depreciates with ecological distance. To test this, we use ancient DNA identity-by-descent segments to construct bilateral migration flows across Western Eurasia over the last 10,000 years. We document four main findings. First, migration flows decline with differences in growing degree days, precipitation, and soil characteristics between origins and destinations. Second, the dimensions of climate that bind vary across subsistence systems: farmers exhibit strong thermal and soil matching, while pastoralists match most strongly on precipitation consistent with differential ecological constraints and limiting factors. Third, periods of warming increase farmer expansion while cooling increases pastoral expansion in patterns that recover known archaeological migration episodes. Migration also acts as a margin of climate adaptation: populations exposed to temperature change move to destinations that partly offset the shift. Fourth, genetic flow predicts subsequent convergence in destination vegetation toward migrants’ ecological profiles, consistent with migration shaping landscape change and the demic diffusion of subsistence practices.
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https://www.rfberlin.com/wp-content/uploads/2026/05/26144.pdf

Locations of major groups, including early farming societies, steppe associated populations, and later Bronze and Iron Age groups.

Migration flows separately by cultural group, revealing substantial heterogeneity in mobility across cultural contexts.

 

[Tautalus]

Several critiques can be made of the paper. One of the critiques concerns the scale and direction of some migrations. The paper argues that populations tended to move toward ecologically similar environments because climate specific knowledge is reduced with environmental distance. Yet several examples they themselves highlight appear to involve movements across extremely different ecological zones. The Yamnaya expansions are a good example. Steppe pastoralists moved not only westward into temperate Europe through the Corded Ware culture horizon, but also eastward into southern Siberia through Afanasievo related expansions. These are not identical ecological environments.
Similarly, later steppe linked populations moved across huge distances from Mongolia into Central Europe. One could argue that these migrations show that technological, social, and political factors sometimes overwhelmed ecological constraints.

A related critique is that the paper may underestimate the flexibility and adaptability of prehistoric populations. Humans are not fixed ecological specialists in the way some animal species are. Farming systems can change crops, pastoralists can alter herd composition, and populations can combine many different subsistence strategies. The spread of agriculture itself often involved adaptation to entirely new climatic zones. Early Anatolian farmers moving into northern Europe had to adopt new crops, alter planting schedules, and develop different survival strategies. This suggests that migration may sometimes have been driven less by ecological similarity and more by innovation and adaptation after arrival.

There is also a broader methodological critique concerning ancient DNA itself. Genetic connections do not directly reveal who moved, why they moved, or how migration occurred socially. An IBD link only shows that some ancestor moved somewhere within several generations. It cannot distinguish elite dominance, gradual intermarriage, trade-network mobility, seasonal mobility, raiding, slavery, or mass population replacement. For example, the spread of steppe ancestry into Europe associated with Corded Ware culture and Bell Beaker culture populations may have involved highly unequal social structures, warfare, or male-biased migration patterns rather than simple ecological sorting.

A further critique concerns the paper’s tendency toward environmental determinism. The argument risks portraying prehistoric migration as primarily constrained by climate and ecology, while potentially downplaying warfare, kinship systems, political alliances, technological innovation, epidemic disease…
For example, the huge Bronze Age expansions associated with steppe cultures may have depended as much on horses, wagons, social organisation, and militarisation as on rainfall patterns or grassland ecology.

The paper is innovative, but several critiques are possible : some migrations seem to exceed the ecological limits proposed, humans may have been more adaptive than the model assumes, genetic evidence cannot fully explain migration mechanisms, and ecology may be overemphasised relative to politics, technology, and culture.​

 

[—BoNe—]

1st — 25 years — 2 ancestors — ~3,800 cM

2nd — 50 years — 4 ancestors — ~1,700 cM

3rd — 75 years — 8 ancestors — ~850 cM

4th — 100 years — 16 ancestors — ~425 cM

5th — 125 years — 32 ancestors — ~213 cM

6th — 150 years — 64 ancestors — ~106 cM

7th — 175 years — 128 ancestors — ~53 cM

8th — 200 years — 256 ancestors — ~26 cM

9th — 225 years — 512 ancestors — ~13 cM

10th — 250 years — 1,024 ancestors — ~6–7 cM

11th — 275 years — 2,048 ancestors — ~3 cM

12th — 300 years — 4,096 ancestors — ~1.5 cM

13th — 325 years — 8,192 ancestors — ~0.8 cM

14th — 350 years — 16,384 ancestors — ~0.4 cM

15th — 375 years — 32,768 ancestors — ~0.2 cM

Russia, Afanasievo I25160.AG 2700 BCE England, Bell Beaker I5512.AG 2300 BCE
19.7 cM

This seems to be the clearest example they have found between Bell Beaker and the steppe populations.

They are separated by 400 years, and since we are talking about long segments of a minimum of 8 cM, we know that this 19.7 cM segment must have been shared through an intermediate “ghost” individual that we do not have in this study.

Therefore, the relationship is not that both share a common ancestor before 2700 BCE; rather, the connection would be a ghost individual who lived around 2500 BCE.

Since Afanasievo does not carry L151>P312 and British Isles Bell Beaker was dominated by P312>L21, we know the connection did not occur through a direct paternal line.

Thus, the most likely relationship would involve female exogamy in an intermediate location, probably a CWC female around 2500 BCE.

Within that interval, we know there would have been at least another 256 individuals (8 generations) sharing that same relationship, and possibly up to 1,000 or even 10,000 more depending on the reproductive rate of that ghost individual.

IBD does not really add anything new to these kinds of studies; we already knew that southern Bell Beaker populations mixed with CWC females. That intermediate component could also, hypothetically, be a South African mtDNA L3 female who married around 2500 BCE a Yamnaya man with flying horses, and the route was Afanasievo → South Africa → British Isles; we will never know. We only know there is a missing intermediate piece.

IBD is not precise beyond 4–6 generations, since it involves too many individuals, and attempting to trace relationships beyond 8 generations becomes speculative.

A minimum threshold of 8 cM already spans roughly ~10 generations and at least ~1,000 individuals sharing that same 8 cM segment.


They use very short segments because otherwise they would not be able to produce any paper.