The speedy, almost comical horse step known as an ambling gait originated in England in the middle of the Ninth Century, scientists say.
The gait, which makes horses comfortable to ride on long journeys, is an inherited trait that springs from a single genetic mutation.
According to this new analysis, it first appeared in horses in York about AD850.
Vikings took these horses to Iceland, and the trait spread globally.
Horses have three essential speeds:
However, a four-beat rhythm, where the horse moves both legs on the same side at the same time has long been a prized feature of some breeds.
Called an ambling gait, the step produces a much smoother ride, particularly over longer distances or rough terrain.
It is as comfortable as a walk but the horse goes as fast as a trot.
In 2012, researchers examined Icelandic horses, and discovered that a single mutation in a gene involved in the movement of limbs was responsible for this ambling ability.
In this new study, scientists extended their search for the origins of this variation of the DMRT3 gene by examining genetic material from 90 horses, some dating back before 3500BC.
The earliest examples they found were in samples from York dating between AD850 and AD900, when the area was being raided and temporarily settled by Vikings.
“The first occurrence of this mutation was in two samples from medieval England from the York Archaeological Collection,” said one of the authors, Dr Arne Ludwig, from the Leibniz Institute for Zoo and Wildlife Research.
“It is unlikely that it was present before, especially not in high frequency, because this is a big advantage, this specific movement of the horses.”
The more comfortable ride offered by these horses would have made them extremely valuable.
Within a few decades, they had turned up in Iceland, probably brought there by Vikings.
The rough Icelandic territory with few roads was a good environment to show off the abilities of these foreign horses and their unusual stepping action.
The locals liked what they saw, and the English imports were rapidly crossbred with the local horse population.
“It looks like the Vikings discovered the advantage of this mutation, and they had the benefit that Iceland had a small population of horses, and it is much easier to fix a trait in a small population than in a population with a huge number of horses,” said Dr Ludwig.
The mutation is now found in many breeds and many different ambling styles exist.
Earlier work has also shown the trait is key to the racing performance of trotting horses.
The study has been welcomed by others in this field.
“It adds significantly to our understanding of the domestication of the horse and especially the role of selection in development of horse breeds beginning over 1,000 years ago,” said Prof Ernest Bailey, from the University of Kentucky, who was not connected to the study.
“The origin of the DMRT3 variant was not widespread before AD900, and the first detection was among horses in the British Isles, with a relatively recent point of origin.
“It was highly selected once recognised, as demonstrated by the rapid increase in the presence of the gene after AD1000.”
While the researchers cannot rule out the possibility that ambling horses were also present in other parts of the world, they believe it is unlikely.
The authors point out that trade was a major element of Viking society, as well as their fearsome reputation for raiding.
They believe this is the most likely route by which the horses were introduced into Asia and the Middle East.
“They fixed the mutation in their stock there in Iceland, and then they have distributed it via trade right around Europe and Asia.” said Dr Ludwig.
The study has been published in the journal, Current Biology.
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