Archaeologists have solved the missing evolutionary link to our beloved domestic horses. Using ancient DNA samples, the researchers were able to identify the genetic homeland of modern horses, revealing that equines first became domesticated by humans some 4,200 years ago.
The study was published in Nature on October 20, and it took a team of 162 scientists who specialized in archeology, palaeogenetics and linguistics. The results point to our modern mounts originating on the steppes in what is now part of southeast Russia, before moving across Eurasia. These breeding lines would go on to replace any existing horse lineages and develop into our current species.
One of the co-authors of the work, Alan Outram, a bioarchaeologist at the University of Exeter, UK, said in an article published on nature.com, “This study has solved a massive mystery, and also fundamentally altered our view of some of the most significant human migrations in prehistory.”
The history of humankind and horses are so intertwined as to be inseparable. With the domesticated horse, armies could mobilize, making warfare and invasions more frequent and successful. But in addition to those uses, horses were used as basic transportation, and for rounding up livestock.
The challenge in dating the domestic horse was the difficulty in being able to distinguish between the bones of a domestic one compared to a wild horse. “Previous work had to be built on indirect evidence, such as killing patterns, tooth damage, traces of consumption of horse milk, symbolic evidence and more,” says lead author Ludovic Orlando, a molecular archaeologist at Paul Sabatier University in Toulouse, France.
Orlando and his team of researchers examined bone and tooth fragments from ancient horses over the past five years. The team gathered over 2,000 samples from various locations around the globe that they suspected could all be contenders for the beginning of the domestic horse. Iberia, Anatolia, as well as the steppes of Western Eurasia and Central Asia, were all in the mix.
Using modern radiocarbon dating to figure out the ages of the samples, the team also used field archaeological techniques to provide cultural context. This would help them figure out if the horses were wild or not. What they discovered was that until around the 4,200 year mark, there were many distinct horse populations in these regions.
What they found was that while the Eurasia region used to have several genetically distinct horse populations, the researchers found a massive change between 2,000 and 2,200 BC. Whereas previously the horses in the area were different genetically, suddenly a single genetic profile that was once confined to the North Caucasus was spreading beyond that area, and replacing all the other wild horse genetic pools within a few centuries. “The genetic data also point to an explosive demography at the time, with no equivalent in the last 100,000 years,” Orlando explains. “This is when we took control over the reproduction of the animal and produced them in astronomic numbers.”
The study’s team went a step further by isolating specific genes that were common in modern horses from the late third century BC. They found a gene called GSDMC, which apparently is associated with hardening of the vertebral discs in humans, causing chronic back issues and pain. Another gene of note was ZRPM1, which is necessary for developing neurons that affect mood regulation and aggression. According to the study, the inactivation of this gene causes anxiety and fear in mice.
The conclusion? “Two variants of the GSDMC and ZFPM1 genes were selected early on during the domestication process, likely facilitating taming, increasing stress resilience and providing horses with a stronger back,” says Orlando. “These qualities may explain why the new horse type had such a global success.”
