Animals

Almost All Horses Today Are Descendants of Arabian and Central Asian Stallions

New genetic analysis reveals the heavy role that human intervention has played in the development of modern horse breeds.

A Lipizzan horse. The Y chromosome sequence that was needed as a template to detect Y variants in any horse was sourced from a stallion of this breed. | Bob Haarmans
A Lipizzan horse. The Y chromosome sequence that was needed as a template to detect Y variants in any horse was sourced from a stallion of this breed. | Bob Haarmans

Horse lovers admire a wide variety of breeds, each with apparently distinctive characteristics and traits. But it may come as a surprise that nearly all horses alive today descend from stallions that were brought into Europe from the Arabian Peninsula and Central Asia over the past 700 years, according to new genetic research.

The study, published in the journal Current Biology, focused on Y chromosomes, which are passed down from fathers to their male offspring. The findings show how heavily human-controlled breeding has shaped the modern horse.

Lead author Barbara Wallner, an animal scientist at the University of Veterinary Medicine in Vienna who specializes in evolutionary biology, explained that all such breeding is done to achieve specific goals. She said that some of these aims have been to produce horses that “run faster and with more endurance, perform better, and are healthy and beautiful. As breeds were formed, these goals were achieved faster by the introgression of foreign breeding studs.”

Wallner and her team could see the hybridization via their Y chromosome analysis of numerous horse breeds as well as related animals. They included a Connemara pony, South German draft horse, English thoroughbred, Warmblood Trakehner, Arabian, Icelandic horse, Lipizzan, Norwegian fjord horse, Shetland pony, Sorraia horse, Warmblood Oldenburg, Warmblood Swiss, Morgan horse, Standardbred, American Quarter Horse, Warmblood Baden Wurttemberg, Warmblood Holsteiner, Warmblood Hanoverian, Warmblood Bavarian, Warmblood Westphalian, French Montagne, Przewalski’s horse, and a donkey.

The thoroughbred American Pharoah won the Belmont Stakes and the first Triple Crown since 1978 at Belmont Park in 2015. | Mike Lizzi

Wallner explained that mutations to the Y chromosome accumulate over time, such that males originating from a common patrilineal ancestor will share a particular collection of Y chromosome mutations forming what is called a haplogroup. These can be difficult to identify, which has hampered past efforts to reconstruct the history of stallions.

For the new study, the scientists overcame prior challenges by using deep, next-generation DNA sequencing. This allowed them to identify even the smallest changes to the 52 Y chromosomes included in the research.

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Combining this chromosome data with written records, the scientists determined that, apart from a few Northern European haplotypes, all modern horse breeds included in the study clustered into a 700-year-old haplogroup. It mostly originated from the Original Arabian lineage of horses from the Arabian Peninsula and the Turkoman horse lineage from the steppes, or grasslands, of Central Asia.

“The purest descendant of the Turkoman horse today is the Akhal-Teke,” Wallner noted.

An Akhal-Teke stallion. | Artur Baboev

The Akhal-Teke’s coat has a distinctive metallic sheen, so the horse appears to literally shimmer in the sun. This breed also has a reputation for high intelligence, speed, and endurance. The breed remains a national emblem in Turkmenistan, whose early tribes prided themselves on their horse breeding skills.

Horses are valued to this day, but because of their central roles in the societies of earlier times, they were prized more than almost anything else.

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“By riding horses, humans were able to travel faster,” Wallner explained. “They could connect huge territories, and the domestication of the horse revolutionized warfare.”

Horse domestication goes back more than 5000 years, so the fact that most horses today descend from lineages dating to just 700 years ago shows how intense breeding from that time onward has greatly affected these majestic mammals.

A similar phenomenon has affected cats and dogs. Like horses, just a few key lineages are at the root of most breeding efforts. These animals, however, bred with local native species, creating the variety of types seen today.

Even mustangs, free-roaming horses of the American West, descended from horses brought to the Americas by the Spanish. Given the new research, it is possible that mustangs too have ancestry going back to a Middle Eastern or Central Asian lineage. Future research could help to solve that mystery, and could identify the history of other horse breeds worldwide.

Additional whole genome studies could also help to determine if the relatively small founding stock of most horses has led to problems due to low genetic diversity or inherited health issues. It may also be that some local, native horses went extinct as a result of human domestication of these mammals.

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