Horse domestication was most likely behind a human migratory revolution that occurred across the vast Eurasian steppe, beginning around 5000 years ago.
Evidence from genetic research published this week show that Western Eurasian farmers living on the steppes around 3000 BC ago were gradually supplanted by mounted warriors from East Asia.
Several waves of migration were behind this crucial population shift, much of it driven by humankind’s emerging relationship with the horse.
University of Copenhagen researcher Eske Willerslev, who led the project in which ancient human DNA was analysed, believes it was horse domestication that drove this change.
The horse, first domesticated on the Eurasian steppes, which sweeps around 8000km from Hungary to China, ushered in a new era of mobility.
“The steppe is like a massive highway, and suddenly you’re getting a car: the horse,” he told reporters. “And everything goes completely crazy.”
For their research, Willerslev and his colleagues analyzed 137 ancient and modern DNA samples from humans and compared the results. The 74 ancient whole-genome sequences studied by the group were up to 11,000 years old and were from inner Asia and Turkey.
The genetic information obtained was compared with that from modern populations across the steppes.
The findings not only point to cultural and tribal shifts in our ancient past, but provide strong pointers to how the horse most likely aided this sea change.
Important questions remain around the origins of horse domestication, but we know that the Botai culture from Northern Kazakhstan and the eastern Eurasian steppes hunted and herded horses there more than 5000 years ago, with evidence they also harvested mare’s milk.
Shortly after, the Yamnaya and Afanasievo horse cultures arose on the western Eurasian steppes. However, this latest genetic testing shows no links between the Botai and these other two horse cultures.
Could the domestication of the horse have arisen independently in different, geographically spread cultures?
This is entirely possible, given recent genetic findings in an unrelated study indicating that the horses kept by the Botai were Przewalski’s Horses, and not the domestic horse, Equus Caballus, with which we are all familiar.
If nothing else, it shows at least one other horse domestication event occurred, and the evidence points to this also being on the Eurasian steppes.
The findings of this latest research also revealed more about the Scythians, a nomadic warrior horse culture that existed from about 800 to 200 BC. Researchers believe they originated in the northern Caucasus or perhaps in Siberia and rode west.
The latest findings now suggest the Scythians were genetically diverse, perhaps a looser confederation of tribes, with at least some genetic links to both proposed points of origin.
The Scythians, like the Huns and Mongols who followed them, were highly mobile on their horses. The Scythians were supplanted by the Huns spreading out of Mongolia. The Hun’s empire folded around 1500 years ago, with other groups spreading from east, including the Mongols.
Overall, the research points to two crucial migratory waves, the first before the Bronze Age and a second during the Late Bronze Age, around 3200 to 4300 years ago.
The first began what was to become a steady west-to-east shift in the genetics of those who lived on the Eurasian steppe.
Eventually trade routes arose. But underpinning it all was the rise and fall of these warrior horse cultures, whose constant movements and military successes led to constant changes in the genetic makeup of conquered populations.
Crucially, however, the most genetic change in this vast swathe has occurred only in the last thousand years.
The domestication of the horse was a milestone in human history that allowed people, their languages, and their ideas to move further and faster than before, leading not only to horse-powered warfare but also widespread farming.
Scholars from around the world have collaborated on a new inter-disciplinary research project, with reports published in the journals Science and Nature.
Much of the study builds on questions raised by scholars of Indo-European studies at the Institute of Nordic Studies and Linguistics at University of Copenhagen.
Several conflicting theories have been presented about who first domesticated the horse, with previous studies pointing to people of the pastoralist Yamnaya culture, a dominant herding group who lived in Eastern Europe and Western Asia.
“The successful spread of the Indo-European languages across Eurasia has puzzled researchers for a century,” explains Dr Guus Kroonen, historical linguist at University of Copenhagen.
“It was thought that speakers of this language family played a key role in the domestication of the horse, and that this, in combination with the development of wheeled vehicles, allowed them to spread across Eurasia from the Yamnaya culture.”
However, as this study shows, domesticated horses were used by the Botai people already 5,500 years ago, and much further East in Central Asia, completely independent of the Yamnaya pastoralists.
A further twist to the story is that the descendants of these Botai were later pushed out from the central steppe by migrations coming from the west. Their horses were replaced too, indicating that horses were domesticated separately in other regions as well.
The study does not find a genetic link between the people associated with the Yamnaya and Botai archaeological cultures, which is critical to understanding the eastward movement of the Yamnaya. Apparently, their eastward expansion bypassed the Botai completely, moving 3000 kilometres across the steppe to the Altai Mountains in Central and East Asia.
Professor Alan Outram from the Department of Archaeology at the University of Exeter and one of the paper’s authors, said: “We now know that the people who first domesticated the horse in Central Asia were the descendants of ice age hunters, who went on to become the earliest pastoralists in the region.
“Despite their local innovations, these peoples were overrun and replaced by European steppe pastoralists in the middle and later Bronze Age, and their horses were replaced too.”
Languages spread through exchanges between several cultures.
The authors also showed that the oldest known Indo-European language, Hittite, did not result from a massive population migration from the Eurasian Steppe as previously claimed.
In contrast to a series of recent studies on population movement in Europe during the Bronze Age, the new results from Asia suggest that population and language spread across the region is better understood by groups of people mixing together.
Gojko Barjamovic, Senior Lecturer on Assyriology at Harvard University, explains: “In Anatolia, and parts of Central Asia, which held densely settled complex urban societies, the history of language spread and genetic ancestry is better described in terms of contact and absorption than by simply a movement of population.”
He adds: “The Indo-European languages are usually said to emerge in Anatolia in the 2nd millennium BCE.
“However, we use evidence from the palatial archives of the ancient city of Ebla in Syria to argue that Indo-European was already spoken in modern-day Turkey in the 25th century BCE. This means that the speakers of these language must have arrived there prior to any Yamnaya expansions.”
The study also shows that the spread of the Indo-Iranian languages to South Asia, with Hindi, Urdu and Persian as major modern offshoots, cannot result from the Yamnaya expansions. Rather, the Indo-Iranian languages spread with a later push of pastoralist groups from the South Ural Mountains during the Middle to Late Bronze Age.
Before entering South Asia, these groups, thought to have spoken an Indo-Iranian language, were impacted by groups with an ancestry typical of more western Eurasian populations. This suggests that the Indo-Iranian speakers did not split off from the Yamnaya population directly, but were more closely related to the Indo-European speakers that lived in Eastern Europe.
In this study, geneticists, historians, archaeologists and linguists find common ground – pointing to increased interaction between the steppe and the Indus Valley during the Late Bronze Age as the most plausible time of entry of Indo-European languages in South Asia.
Several authors of the paper had radically conflicting views before the final interpretation was achieved.
Lead author on the article, Peter de Barros Damgaard, a geneticist at the University of Copenhagen, comments: “The project has been an extremely enriching and exciting process.
“We were able to direct many very different academic fields towards a single coherent approach. By asking the right questions, and keeping limitations of the data in mind, contextualizing, nuancing, and keeping dialogues open between scholars of radically different backgrounds and approaches, we have carved out a path for a new field of research.
“We have already seen too many papers come out in which models produced by geneticists working on their own have been are accepted without vital input from other fields, and, at the other extreme, seen archaeologists opposing new studies built on archaeogenetic data, due to a lack of transparency between the fields.
“Data on ancient DNA is astonishing for its ability to provide a fine-grained image of early human mobility, but it does stand on the shoulders of decades of work by scholars in other fields, from the time of excavation of human skeletons to interpreting the cultural, linguistic origins of the samples. This is how cold statistics are turned into history.”
Kroonen adds: “The recent breakthrough in ancient genomics poses challenges for archaeologists, linguists and historians because old hypotheses on the spread of languages and cultures can now be tested against a whole new line of evidence on prehistoric mobility.
“As a result, we now see that geneticists are driven by key questions from the humanities, and that research within the humanities is energized by the influx of new data from the sciences. In the future, we hope to see more cross-disciplinary co-operations, such as the one leading to this study.”
137 ancient human genomes from across the Eurasian steppes
Peter de Barros Damgaard et al.
Nature (2018) doi:10.1038/s41586-018-0094-2
The abstract can be read here.
The first horse herders and the impact of early Bronze Age steppe expansions into Asia
Peter de Barros Damgaard et al.
Science May 9, 2018: doi:10.1126/science.aar7711
The abstract can be read here.