Horses revolutionized human history with fast mobility. However, the timeline between their domestication and widespread integration as a means of transportation remains contentious. In new research, scientists from the Centre d’Anthropobiologie et de Génomique de Toulouse and elsewhere assembled a collection of 475 ancient horse genomes to assess the period when these animals were first reshaped by human agency in Eurasia.
Librado et al. found that reproductive control of the modern domestic lineage emerged around 2,200 BCE. Image credit: Vera Khramova.
Horses revolutionized human history by increasing mobility, but the timeline between domestication and widespread integration as a means of transportation remains contentious.
Genetic evidence suggests that modern domestic horses emerged in the western Eurasian steppes, including in regions that were populated by herders known as the Yamnaya around 3,000 BCE.
Some theories suggest that the Yamnaya rode horses as they migrated into Europe.
The earlier appearance of a different lineage of domestic horse (potentially used for their milk), associated with the Botai culture in Central Asia (from a context dating to around 3,500 BCE), adds to the confusion.
To probe the potential timings of domestication, Dr. Ludovic Orlando from the Centre d’Anthropobiologie et de Génomique de Toulouse, Dr. Pablo Librado from the Institut de Biologia Evolutiva of Barcelona and their colleagues performed genomic analyses of 475 ancient and 77 modern horses.
“I have started working on horses about a decade ago. At that time, we only had a handful of ancient genomes,” Dr. Librado said.
“With this new work, we now have several hundreds. It was particularly important to gain resolution into Central Europe, the Carpathian and the Transylvanian basins, as this area was central to ongoing debates about horseback riding driving the massive migrations from the steppes around 5,000 years ago, and possibly earlier.”
The researchers found that around 2,200 BCE there was a distinct change in horse breeding practices (including the introduction of close kin mating), which led to the replacement of nearly all horse lineages with modern domestic bloodlines.
This expansion was preceded by a domestication bottleneck (starting around 2,700 BCE) in which generation time (relating to the age of horses when they reproduce) was reduced, thereby facilitating the breeding of the new domestic horses.
Previous research suggests that the Yamnaya migration took place 3,300-2,600 BCE.
Therefore, the timings from this study are incompatible with the hypothesis that Yamnaya-related steppe peoples were accompanied by large herds of modern domesticated horses.
The authors also found evidence for domestication in the Botai horses (including shortened generation times), which means that horse husbandry may have taken place in some regions prior to 2,700 BCE but did not lead to widespread horse mobility.
“One question that puzzled me for years pertains to the scale of the production: how could such a substantial number of horses be bred so suddenly from a relatively small domestication area to meet the increasingly global demand by the turn of the second millennium BCE?” Dr. Orlando said.
“Now we have an answer. Breeders controlled the reproduction of the animal so well that they almost halved the time interval between two generations.”
“Put simply, they were able to accelerate the breeding process, effectively doubling their production rate.”
“Our methodology for measuring temporal changes in generation times holds great potential,” Dr. Librado explained.
“It arms the archaeozoological toolkit with a new way to monitor the development of controlled breeding across various domestic species beyond horses.”
“But it can also help elucidate the generation interval in our hunter-gatherer ancestors and how these intervals evolved alongside shifts in lifestyle or significant climatic changes.”
“Our evidence supports two domestications in horses,” Dr. Orlando said.
“The first, occurring around 5,500 years ago, aimed to address the decline in horse populations and provide sustenance for populations inhabiting the steppes of Central Asia.”
“The domestic horse as we know it emerged around 4,200 years ago from the second domestication.”
“This one truly transformed human history by providing fast mobility for the first time.”
The study was published this week in the journal Nature.
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P. Librado et al. Widespread horse-based mobility arose around 2,200 BCE in Eurasia. Nature, published online June 6, 2024; doi: 10.1038/s41586-024-07597-5
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