Mys­tery of man and horse deep­ens with ge­netic map­ping

China Daily (USA) - - ACROSS AMERICA - Chris Davis Con­tact the writer at chris­davis@chi­nadai­lyusa. com.

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 smooth tolt gait is ideal for cov­er­ing long dis­tances in the sad­dle and, as can be imag­ined, shoot­ing bows and ar­rows or us­ing any other weaponry. Other breeds of horses can learn the tolt, with ex­ten­sive train­ing, but for some, it just comes nat­u­ral be­cause it’s in their blood, some­thing that was no­ticed and sug­gested by Wil­liam Bate­son, one of the fa­thers of ge­net­ics, in 1907.

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.”

PRO­VIDED TO CHINA DAILY

Han Dy­nasty bronze “Pac­ing Horse Poised on Swal­low with Wings Out­stretched” could hold se­crets.

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