Use of horses became widespread only around 2200 BCE, finds Nature study challenging timeline

For the study, researchers from France analysed genomes of 475 ancient horses to conclude that widespread horse domestication likely didn't occur before 2,700 BCE.

Representational image | Photo: Antara Baruah/ThePrint

Bengaluru: The timeline and geography of horse domestication has been unclear, with the issue continuing to be controversial and even politically contentious. A new study published in Nature Thursday has concluded that widespread horse domestication likely did not occur before 2,700 BCE.

For the study, titled ‘Widespread horse-based mobility arose around 2,200 BCE in Eurasia’, researchers from France analysed over 400 ancient horse genomes.

The findings challenge previous conclusions from studies that point to earlier domestication times, particularly the theory that herder populations called Yamnaya from the western Eurasian steppes rode horses and migrated into Europe around 3,000 BCE.

The authors do not dispute the other theory of a separate lineage of horses called Botai horses that were domesticated in Central Asia, currently being speculated as having occurred around 3,500 BCE. In fact, they state their findings show evidence for this domestication, adding that it was, however, not widespread and occurred locally.

The study further states that the time period from 2,700 BCE to 2,200 BCE was a “domestication bottleneck” for horses, where the age of breeding reduced, thus facilitating the breeding of more horses.

Around 2,200 BCE, horse breeding practices began evolving, including close kin mating, which eventually led to a replacement of nearly all horse lineages with the current modern domestic lineage.

Additionally, the researchers also managed to establish Botai culture as dependent on horse husbandry for dairy and hunting, as opposed to long-distance mobility, which occurred later.

Horse domestication mysteries

Horses have historically provided humans with rapid mobility and have been used by humans across the globe. But the history of horse domestication, and especially the period between first attempts at domestication and widespread integration as a means of transport, continues to be unclear.

The earliest complete archaeological evidence of horse as use of means of transport dates back to 2000 BCE, but is that of chariot burials, indicating that they had become widespread by then.

Current theories, based on a wide variety of genetic, anthropology, and linguistic studies, state that horses were domesticated in the Eurasian steppes approximately around 3000 BCE and slightly earlier, while independent discoveries in modern-day Kazakhstan regions show a separate lineage of horses domesticated by the Botai culture even earlier in 3500 BCE.

The Botai lived a subsistence economy centered on horses, with theirs having had a distinct lineage from the modern horse. Evidence of horses being used for subsistence predates evidence of widespread adoption for transport, with horse milk peptides discovered in human teeth dating back to 3,500 BCE.

Horse integration into society as a means of transport was aided by the development of Sintashta spoke-wheeled chariots in Asia, dating to around 2,200 to 1,800 BCE. Until then, the modern horse seemed to not have existed genetically, with those outside of western steppe regions being those of a completely different genetic lineage — the Botai, which went extinct after a 5,500-year existence.

Study findings

According to existing studies, the genetic makeup of the modern domesticated horse (called DOM2 in genetic parlance) came about in the Western Eurasian steppes, the grassland and savannah regions spread across modern-day Eastern European states, at some point in the third millennium BCE (3000 BCE to 2001 BCE).

The authors of the paper studied the genomes of 475 ancient horses to determine when DOM2 began to spread as the dominant lineage, replacing domesticated lineages. To identify this, they analysed when DOM2 numbers were large enough to sustain global spread in the 200 generations of horses that preceded the years around 1864 BCE, which is the average date of the most detailed DOM2 sequence we have.

Based on genetic analysis and assuming a pure-modern veterinary lifespan of 8 years, the team estimates that horses became widespread around 2190 BCE. They state that these findings are also supported by the first depictions of horses in Akkadian cave art (modern-day Middle East), and also the first records of conflict among humans, including in places like the Balkans, Egypt, and the Indus Valley.

The demographic reconstruction performed by the scientists also shows the first evidence of a strong bottleneck in horse domestication in the 75 generations preceding this DOM2 expansion. This directly contradicts the theory that when steppe people were migrating into Europe, various lineages of horses also migrated with them. The findings show that there was a “plummeting availability” of DOM2 reproductive horses, indicating that the method of migration was something else.

However, they also found that the first evidence of horses being bred for efficient DOM2 transport bloodlines can be traced to Central Asia and Anatolia (modern-day Turkey).

The team also uncovered new evidence of horse husbandry at Botai. In the analysis of 36 horse genomes from here, they found no evidence of inbreeding, but there was evidence of their shortening sexual maturity ages.

Paleoclimate data in the region indicates humid conditions with no forests, which were favourable to an economy that could subsist on horses, state the authors. This would include dairy as well as riding horses for hunting in short bursts, as genetic evidence indicated they were not bred for long-distance horseback riding.

Major conclusions

The authors conclude by stating that the findings show that horse genomic makeup remained fully local to central Europe and the central Asian regions until the third millennium BCE.

The spread of the DOM2 bloodline was rapid, and quick mobility provided by horses was immediately succeeded by a “monumental” increase in connectivity and trade. The findings mirror those from archaeological records, which shows a huge spread of horses in Asia and Near East during the time period.

The team adds that their research further confirms Botai as a central Asian steppe region where horse domestication occurred for horse husbandry before for mobility.

In the paper, the authors also state that their method for identifying the lowering of reproductive age to increase populations can also be extended to studying other ancient hominins such as Neanderthals and Denisovans.

“Our work opens for a new line of research investigating the possible consequences of past and present environmental and epidemiological crises on the reproduction of both human groups and other species,” they conclude.