Modern Horses Faster Than Their Ancestors

This graphical abstract summarizes horse genetic history over the last 5,000 years. Courtesy of Fages et al./Cell

(CN) – The fall of the Persian Empire in the 7th century and modern breeding practices both played a part in how horses have changed over the last 5,000 years and a snapshot of that timeline is presented in a new study published Thursday.

Long before the Kentucky Derby became known as one of the most esteemed thoroughbred horse races in the world, there were horses that roamed the Iberian Peninsula and Siberia 4,000 – 4,500 years ago that are now extinct.

According to a study published in the scientific journal Cell, those two recently discovered horse lineages were not necessarily fast animals. It was only in the last 1,500 years that ambling and trotting over short distances became more common and sought after in horses.

Two groups make up the known lineages for modern horses, including the domestic horse and the Przewalski horse, also known as the Mongolian wild horse.

The two extinct groups would be considered the horse equivalent of what Neanderthals are to modern humans, according to molecular archaeology professor Ludovic Orlando from the University of Copenhagen.

The recently discovered horses have no modern-day ancestors.

Researchers included a team of geneticists, archaeologists and evolutionary biologists from 85 institutions around the world who examined the genome-scale data of horses from over the last 42,000 years. That included 278 samples taken from across Europe and Asia.

While horses have played a significant role in the way human history has been shaped, major world events also played a part in how the modern horse was molded.

Sometime around the 7th and 9th centuries, a significant shakeup shifted the genetic makeup of horses in Europe and Central Asia. Researchers say this likely corresponds to Islamic expansions because horses commonly found in Europe at a previous time are now only found in Iceland.

Meanwhile, other horses from after that time period were much more like horses found in Persia during the Sassanian Empire, the last pre-Islamic Persian empire that fell in 651 AD.

“It was a moment in history that reshaped the landscape of horses in Europe. If you look at what we today call Arabian horses, you know that they have a different shape–and we know how popular this anatomy has been throughout history, including in racing horses. Based on the genomic evidence, we propose that this horse was so successful and influential because it brought a new anatomy and perhaps other favorable traits,” Orlando said.

When the team performed a scan to identify genes that had been selected for breeding in these Persian horses, they found evidence of selection in genes associated with body shape.

“Such a large collection of data means that we can build a much more precise understanding of horse domestication and management through space and time,” Orlando says. “But it was truly an interdisciplinary effort because of course it takes a lot more than just DNA to understand such a story. We had to integrate all these social, historical, and geographical aspects.”

There was also a steep decline in overall genetic diversity of the domestic horse in the last 200 to 300 years. Researchers believe this decline corresponds with new breeding practices that were introduced with the rise of the concept of “pure” breeds.

The timeline presented in the study still leaves open some gaps in horse history, but the biggest question researchers were unable to answer was how the modern horse became domesticated.

“Whenever I’m asked about what finding I’m most excited about, I always say, the next one,” Orlando said, “because this research opens the door for so many possibilities to be studied now.”

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