A Single Mutation Made It Easier to Ride Horses

By Nathaniel Scharping | August 9, 2016 3:25 pm
gaited-horses

This 19th-century image shows a horse pacing. Note that the legs on each side move at the same time. (Credit: USC Digital Library/Wikimedia Commons)

Horses normally move about in one of three ways: they walk, trot or gallop. The middle gait, the trot, is a horse’s Goldilocks stride — not so fast that it gets tired, but not so slow that it gets left in the dust.

Unfortunately for the humans that like to ride on horses’ backs, the trot is a pretty uncomfortable gait. During a trot, a horse will lift two legs at a time in diagonal pairs, alternating sets as it goes. This is a very economical motion for the horse, as it requires little extraneous compensation to stay balanced. If you happen to be sitting astride that horse, however, it feels more like riding in a truck with no shocks over a backcountry road — bouncy only begins to describe it.

Smoothing the Ride

To compensate, most riders develop a kind of rolling motion that smoothes the ride out, but a full day on horseback results in burning legs and an aching back. For this reason, horses that have developed a special kind of gait in place of the trot are highly prized. Called the amble, and only seen in some breeds, this four-beat stride involves moving both legs on the same side at one time, as opposed to diagonally. Horses that amble, called gaited horses, can move at the same speeds as other horses, but do so without the ceaseless up-and-down of their trotting counterparts.

Back in 2012, researchers from Sweden tied the amble to a very specific region of the genome, a single nucleotide to be exact. They found that a mutation of the DMRT3 gene altered the way that a horse trots, shifting its gait from the diagonal-pair trot to the same-side amble. After studying the mutation in mice, they think that the gene controls the development of the spinal cord in a region responsible for limb locomotion. Mice with the mutation exhibited a longer stride length, something that in horses could serve to change the pattern of their footfalls.

Mutation Spread Quickly

Now, a team of researchers from the Leibniz Institute for Zoo and Wildlife Research, some of whom contributed to the 2012 study, says it’s found where this mutation came from. The researchers analyzed DNA from 90 ancient horses dating to over 5,000 years ago, and found the first instance of the mutation occurred in two horses from the York Archaeological Collection, dated to between 850 and 900 A.D.

The horses originated in medieval England, they say, and were likely taken to Iceland by the Vikings, where they were interbred to produce a population of the gaited variety. From there, these superior comfortable horses spread across Europe, resulting in the wide distribution and diversity of gaits evident today. They published their findings Monday in the journal Current Biology.

The researchers think that the explosion of horses with this particular mutation so soon after it appeared is good evidence of our own species meddling in the horses evolution. Today, horse breeds ranging from the North American Saddlebred to the Indian Kathiawari possess the ability to amble. Gaited horses possessed a new and valuable trait, leading us to preferably breed them and artificially select for a particular mutation. It is not clear if the new type of stride offers any natural evolutionary advantage to the horses, besides making them better suited for our own needs.

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  • http://www.RNA-mediated.com jvkohl

    See: Codon identity regulates mRNA stability and translation efficiency
    during the maternal-to-zygotic transition

    All serious scientists know that selection for energy-dependent codon usage must occur in the context of fixation of RNA-mediated amino acid substitutions via the physiology of reproduction in all living genera. Claims that artificial selection by humans link a mutation in horses that makes them easier for us to ride are based on the pseudoscientific nonsense touted by neo-Darwinian theorists.

    • Lorenzo Montana

      Could you please tell us where it’s said that artificial selection leads to the mutation? Actually nowhere, it leads to the spread of the mutation, your comment is just off topic

      • http://www.RNA-mediated.com jvkohl

        You obviously do not understand the complexity of the topic or anything about systems biology in the context of cause and effect.

        See also: “Animals actively use at least half of the genome” at bioRxiv

        What motivates you, and others like you, to try and separate the origin of the mutation from its spread through a population? Did you learn that virus-driven energy theft is the cause of the mutations, which are linked to all pathology? Are you waiting for someone to save neo-Darwinian theory from more attacks by those who are biologically informed?

        • Lorenzo Montana

          “Claims that artificial selection by humans link a mutation in horses that makes them easier for us to ride…”. As far as I know it’s a random mutation that appeared, it’s a common phenomena. As this variation was preferred by men, horses possessing it were in advantage for the reproduction.

    • Lorie Franceschi

      Question then: If humans did not use breeding in horses to get the gaiting trot then how did we get some many different breeds of dogs? There are genealogical trees of dogs and how they were bred to get a type of dog breed we have today. So humans can’t do that and it is nonsense touted by neo-Darwinian theorists. Nice.

  • http://www.smokershistory.com/ CarolAST

    Why would this require a mutation anyhow? It’s just a different way of using the same physical equipment.

  • JoanHendricks

    There is something substantial missing in this blog. And, I say this as a lifetime horse owner and rider, not a scientist. The pace is not smoother than the trot. Pacing is used for sulky horse racing as the horses can run faster on the track when pacing than when trotting. Gaited riding horses have a different gait – more like a running walk where the gait is the same as the walk but faster. I’m not doubting some mutations brought about the ability of some horses to do a comfortable riding riding gait (some breeds are: Tennessee Walking horses, Paso Finos and Peruvian Pasos, Kentucky and Rocky Mountain horses) but those gaits are not the pace.

  • S_herbert

    Dear Author, you do not mean to keep using the word pacing. You mean gaited or racking. The scientific study you reference calls it ambling. It is true, some saddlebreds (my experience) amble and are notably easier to train to slow gait and rack. Horses that pace are seriously uncomfortable, while gaited horses are smooth.

  • LeslieFish

    If this mutation was so valuable to humans, why do most horses in the world today trot instead of pace? After all these thousands of years that humans have been riding horses, why are pacers still so rare?

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