The study is a follow-up to the discovery in 2012 that the ability to amble can be traced to a single gene mutation. It’s called DMRT3 or, colloquially, the “gaitkeeper” mutation.

In the new study, the researchers analyzed DNA from the remains of 90 ancient horses. They found the gaitkeeper signature in horse samples from England dating back to the 9th century. They also found the mutation in early Icelandic horses from the 9th to 11th centuries. When they looked at horses from the same time period in mainland Europe, however, they failed to find the gene.

In the 9th century, Vikings occupied parts of England that had ambling horses, said Arne Ludwig, an evolutionary geneticist at the Leibniz Institute for Zoo and Wildlife Research in Berlin, and an author of the paper.

He believes Vikings pillaged English horses and sailed to Iceland with them. There, horses with the ability to amble became dominant as people bred animals that were easy to ride for long distances across terrain without roads.