Detecting an Intelligently Designed Mutation in Horses - Evolution News & Views

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Detecting an Intelligently Designed Mutation in Horses

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If early humans spread a mutation without knowing what a mutation is, is that a case of intelligent design? Here is a case involving horses.

Horses typically have three natural gaits (patterns of leg placement in motion): the walk, the trot, and the gallop. Horseback riders know that the natural trot is bouncy, and with some horses, a natural gallop is, too. Yet horses with extra gaits can be found worldwide that prance with a minimum of bounce or gallop smooth as an arrow. What happened?

An open-access paper in Animal Genetics explains that horses have been bred for smoother gaits for thousands of years. Humans have looked for specimens that could be trained to walk in "unnatural" gaits that were less bouncy, and by artificial selection, mated them to form new breeds. The popular breeds, being more useful to man, would be traded from place to place, increasing their numbers, till some spread around worldwide. The authors say,

For centuries, domestic horses have represented an important means of transport and served as working and companion animals. Although their role in transportation is less important today, many horse breeds are still subject to intense selection based on their pattern of locomotion. A striking example of such a selected trait is the ability of a horse to perform additional gaits other than the common walk, trot and gallop. Those could be four-beat ambling gaits, which are particularly smooth and comfortable for the rider, or pace, used mainly in racing. Gaited horse breeds occur around the globe, suggesting that gaitedness is an old trait, selected for in many breeds. (Emphasis added.)

Early breeders knew what they wanted, and understood how to achieve it on a macro level, but could not have understood the underlying cause. The genetic basis has recently come to light: it's a nonsense mutation in a gene named DMRT3.

A recent study discovered that a nonsense mutation in DMRT3 has a major impact on gaitedness in horses and is present at a high frequency in gaited breeds and in horses bred for harness racing. Here, we report a study of the worldwide distribution of this mutation. We genotyped 4396 horses representing 141 horse breeds for the DMRT3 stop mutation. More than half (2749) of these horses also were genotyped for a SNP situated 32 kb upstream of the DMRT3 nonsense mutation because these two SNPs are in very strong linkage disequilibrium. We show that the DMRT3 mutation is present in 68 of the 141 genotyped horse breeds at a frequency ranging from 1% to 100%. We also show that the mutation is not limited to a geographical area, but is found worldwide. The breeds with a high frequency of the stop mutation (>50%) are either classified as gaited or bred for harness racing.

The authors describe how some breeds can never learn new gaits, some learn it only through diligent training, and others learn them naturally. Those with neurons containing the mutation in DMRT3, which plays a pivotal role in coordinating limb movements, are able to perform the desired gaits. Wild horses, such as Przewalski's horse (pictured above), cannot.

Screening several horse breeds for the DMRT3 mutation revealed that the occurrence of this mutation is dichotomous with an allele frequency of nearly 100% in six tested gaited breeds and zero in seven tested non-gaited breeds and in the [wild, never-domesticated] Przewalski's horse. In addition to the strong association with ambling gaits, this mutation was shown to occur in breeds used for harness racing, pacers as well as trotters.

A news release from Wiley, publisher of the paper, mentions a striking case: the Paso Fino breed from Latin America has a gait so smooth "you can have a glass of wine in your hand without letting it spill." That breed has 100% frequency of the DMRT3 mutation.

So that's the data. A specific single point mutation appears to be associated with the ability to perform gaits that are beneficial to humans. If you were a geneticist unfamiliar with that association, would you know the mutation was spread by humans? Probably not.
 
Here is an interesting test for the Design Filter. The mutation could have been caused by chance. By all appearances in a genetics lab, it is a nonsense mutation -- an accident of little or no consequence. No natural law would have caused the mutation.

But then, say, the forensic scientist finds an association between the mutation and limb coordination. Is that by chance? It could be; perhaps natural selection favored the horses that could do extra dance steps to distract predators or attract mates. That appears improbable, however. For their survival needs, horses need to walk and run, not prance before kings or pull harness carts smoothly. If horses benefited from the mutation, it would be widespread in wild horse populations.

It's the worldwide distribution of this mutation and its strong association with traits desirable to humans that drops this mutation beyond chance and natural law and into the design category. The same forensic reasoning could be applied in other cases:

Few animals have been of such great value to humans as horses when it comes to means of transportation. All over the world, horses have been used for everyday transportation, in military settings, cattle herding and agricultural power, pulling carriages and carts, pleasure riding or racing. Over the centuries, horse populations and breeds have been shaped by humans based on the different purposes for which the animals were used.

What's interesting about this so-called "gait keeper" mutation is that the humans didn't have to know how it worked at the cellular level. They just had a purpose, and did whatever worked to achieve it. A design inference is warranted no less than if they had specifically targeted the DMRT3 gene to reach their goal.

This is not so different from any intelligent design case. Designers do not always exhaustively know the particulars. When early humans painted artwork on cave walls, they didn't need to know how the molecular structure of the paint caused it to adhere to rock. The discoverers of the Rosetta Stone did not have to be able to read hieroglyphs to infer that the markings contained a message. A software programmer can write in a high-level language without comprehending the machine language several levels down. Her boss who designs the system with its information flow may not even know how to program at all.

One little mutation in one little gene: it slipped through the Design Filter and became an inference to intelligent design.

Photo: Przewalski's horse at Khustain Nuruu National Park, Mongolia/Wikipedia.