Horse DNA reconstructs the history of their domestication

Horse DNA reconstructs the history of their domestication

Horses weren't always bred for participate in races or be displayed for their beauty. In fact, humans have been employing the equine race for these activities for less than previously thought.

What's more, speed over short distances is a trait that started to be interesting only 1,500 years ago.

This has been one of the main findings from an international team of scientists led by Ludovic Orlando, an expert from the National Center for Scientific Research (CNRS) and the University of Toulouse (France). The work is published this week in the Cell magazine.

His study reconstructs the history of the domestic horse during the last 5,000 years thanks to the largest collection of genomes ever studied (apart from human). Genetic analysis of 278 horses from across Eurasia has revealed two new lineages of now-extinct horses, hitherto unknown.

The results of Orlando and his team also show a sharp decline in horse genetic diversity over the past 200 to 300 years. Experts believe that this decline is due to breeding practices that were introduced with the emergence of the concept of 'purebreds'.

"What we imagine as a horse today and what we imagine as a horse a thousand or two thousand years ago is probably very different," says Orlando.

Pablo Librado, a Spanish researcher from the Orlando group and co-author of the study, says that "horses have experienced a reduction of approximately 14-16% in their genetic diversity." This loss of diversity has had indirect consequences, for example, because of consanguinity.

“Using a few stallions as breeders has meant that a foal is more likely to have problems in development and reproductive capacity. The number of deleterious mutations - which do not cause death, but rather a decrease in the individual's ability to survive or reproduce - has increased by approximately 4% in modern horses, compared to older horses, ”says Librado.

According to the authors, some of the traits we are most familiar with in horses they are just a modern invention since the genome has actually been modified more in the last 200 years than in the previous 4,000 years of domestication.

“Such a large collection of data has allowed us to accurately understand horse handling,” explains Orlando. “However, it takes a lot more than DNA to understand such a story. We had to integrate all the social, historical and geographical contextual aspects ”, explains the expert.

"In the historical record, from the Bronze Age onwards, horses have always been part of the equation until recently, connecting civilizations and impacting transportation, warfare and agriculture," he adds.

The conquest of Europe on horseback

The authors have tried to understand how human beings and their activities transformed the horse throughout history to adapt it to their purposes and, in the same way, how these changes also influenced the history of mankind.

“Many human civilizations have expanded thanks to their horses in the last millennia. Each time they conquered a new area, humans displaced entire populations of indigenous horses. One of the most recent was the Islamic expansion, ”says Librado.

The researchers observed a major change in the genetic makeup of horses in Europe and Central Asia in the 7th to 9th centuries. "This change probably corresponds to Islamic expansions since, before that time, horses common in Europe were only found in regions like Iceland," the authors note.

The team performed a scan to identify genes related to Persian horses. After analysis, they observed that European horses were much more similar to the horses found in Persia during the Sassanid empire, after these expansions.

“It was a moment in history that remodeled the landscape of horses in Europe. If we look at what we now call Arabian horses, we know that they have a different shape, and we know how popular this anatomy has been throughout history, ”says Orlando.

"Based on genomic evidence, we consider this horse to be so successful and influential because it brought a new anatomy and perhaps other favorable traits," he adds.

Two new horse lineages

Librado already demonstrated in one of his previous works the existence of two different horse lineages after analyzing the fossil remains found in Botai (the first archaeological site with evidence of domestication, located in Kazakhstan).

These were not compatible with the DNA of modern horse ancestors and they evidenced the existence of a new equine. “It was surprising to discover that Botai's domestic horses are the ancestors of what was believed to be the last wild horses, Przewalski's horses,” says the expert.

However, thanks to the work of Orlando and his team, to these current lineages are now added two additional lineages of horses, one from the Iberian Peninsula and the other from Siberia, which existed 4,000-4,500 years ago.

“We find these new lineages in the extremes of Eurasia that are not related to what we now call the domestic horse, nor to the Przewalski horse. They are a kind of horse equivalent to what Neanderthals are to modern humans, ”says Orlando.

“One of these wild horses corresponds to Equus lenensis, whose habitat was believed to be restricted only to the more Holoartic region of Siberia. In addition to Siberia, our data show that it was also present in the Republic of Tuva, on the border of present-day Mongolia, ”says Librado. DNA analysis shows that E. lenensis survived until at least 5,100 years ago.

On the other hand, "the DNA extracted from four horses that lived 4,800-4,000 years is totally different and, therefore, belongs to a probably Iberian lineage that until now was unknown," adds the researcher. This Iberian lineage survived a few more generations, given that scientists found its genetic influence in another horse that lived 2,700 years ago.

"But nevertheless, we rule out that this Iberian lineage may be the ancestor of modern domestic horses. In fact, it exchanged little genetic material with current domestic horses, making a very poor contribution to the domestication process ”, concludes the author.

Bibliographic reference:

Fages et al: "Tracking five millennia of horse management with extensive ancient genome timeseries”, May 2019, Cell, DOI: https://www.cell.com/cell/fulltext/S0092-8674(19)30384-8.


Video: A Story Of The Przewalski Horse, The Last Truly Wild Horse u0026 Its Comeback