Mystery of man and horse deepens with genetic mapping

The well-known second century AD Han bronze sculpture titled Pacing Horse Poised on a Swallow with Wings Outstretched may hold a clue to one of the many mysteries of the horse - How did it spread throughout Eurasia: East to West or vice versa?

Animal scientists have been looking closely at the genetics behind a particular gait that not all horses can pull off. Most horses have basically four gears - walk, trot, canter and gallop.

But some, most notably Icelandic horses, have a fifth speed, called variously the tolt, amble, or smooth ride. It is like a fast walk, and can be faster than a trot, but unlike the trot, does not lift the horse into the air or bounce the rider up and down in the saddle. It's more like sitting on a jiggling washing machine during the spin-dry cycle.

The Vikings brought the smooth gait horses to Iceland 800 years ago (supposedly pillaged from England) and have been fiercely protective of the breed ever since. To this day, no other breed of horse is allowed to set hoof on the island nation, and once an Icelandic horse leaves the country, it may never return.

This protectionism has led to a breed that is incredibly well-adapted to the terrain, but it is not the only breed that can perform the tolt - the Brazilian Campeiro, the Indian Marwari, the Puerto Rican Paso Fino, even the Tennessee Walker are a few examples.

In 2012 scientists isolated the talent to tolt to a single gene mutation called DMRT-3, quaintly nicknamed the "gait-keeper" gene.

In a follow-up study just published, a team set out to map the worldwide distribution of the gait-keeper mutation and the results, in that great way science has of stirring things up, raise more questions than they answer.

The scientists collected DNA samples from 141 breeds of horse ancient and contemporary, from Hokkaidos in Japan to Kirgiz in Kyrgyzstan to Warmbloods in Sweden and Timor Ponies of Indonesia.

The study showed that the mutation was spread all over the world, showing up in just under half (68) of all the samples.

"It is still unclear where the mutation arose," the study concludes. "A large-scale analysis of the whole haplotype should she more light on this intriguing question."

One suggested scenario has the Vikings trading their horses at ports of call along the Caspian Sea and Middle East and buyers, prizing the advantages of the smooth gait, breeding them with their herds to bring out the trait.

"This study is a good example of how horse and human history are inexplicably intertwined," Samatha Brooks, a professor of horse physiology at the University of Florida told The New York Times.

The Viking story is considered the most plausible interpretation of the data, but the study's lead author himself says not so fast.

Lief Andersson, professor of animal genetics at Uppsala University in Sweden, said it's possible that the mutation arose in East Asia and spread westward from there.

"We had access to Mongolian and local Japanese horses," Andersson wrote in an email to China Daily. "We tried to get access to samples from local Chinese breeds but there were no Chinese colleagues that were able to send us any."

Andersson did note that a group of Chinese scientists had recently found the mutation was in some Chinese horses.

"Furthermore there is a very famous bronze sculpture of a pacing horse that was found in a tomb from 200 AD," he said. "Of course this does not prove that the mutation was present in China already 2000 years ago, but I think it is quite likely."

Contact the writer at chrisdavis@chinadailyusa.com.