Classic polar: the first domestic horses could have appeared outside Central Asia
The researchers who turned the history of horse domestication upside down by results published last week do not rule out the possibility that modern domestic animals originated outside of Central Asia.
The first credible evidence of the domestication of horses dates back to the Botai culture, which is said to have tamed horses in northern Kazakhstan around 3500 BC.
Until last week, models suggested that all modern domesticated horses descended from those first tamed by the Botai people.
But scientist Ludovic Orlando and his colleagues, writing in the journal Science, reversed that belief last week.
Their DNA tests revealed that Botai horses did not give birth to today’s domesticated horses, but were in fact the direct ancestors of Przewalski’s horses.
Surprisingly, Przewalski’s horse, commonly considered to be the last true wild horse in existence, is in fact the descendant of the first horses ever to be domesticated.
Przewalski’s horses (Equus ferus przewalskii) are a different species from the modern domestic horse (Equus caballus), with a different number of chromosomes.
Thus, the site of the first domestication of E. Caballus, which we all know, remains shrouded in mystery.
“With the genomic data we currently have, it is impossible to locate the source that gave birth to the modern horse,” says Orlando, professor of molecular archeology at the University of Copenhagen, Denmark, and research director at the ‘French National Institute. Scientific research center.
What is clear, however, is that none of the ancient Eurasian horses the team has analyzed so far over the past 4,100 years relate to Botai.
Models of mitochondrial DNA variation also indicate that the horse population expanded dramatically around 4,100 to 5,000 years ago.
So it appears that humans encountered and developed a new type of domesticated horse around this time, and this horse became extremely popular and perhaps even facilitated the expansion of human populations.
“We are looking at a series of candidate locations that are known sources of major human expansions in the third millennium BCE,” Orlando said.
Interestingly, the earliest currently sequenced fossils of this new type of horse come from Hungary, Romania, and the Pontic Caspian Steppe. The team therefore does not rule out a possible origin outside Central Asia.
Antoine Fages, a doctoral student in the Orlando team who carried out the experimental work for the study, said: “This work clearly illustrates the power of harnessing the sequencing of the old genome. This really allows us to uncover a series of key evolutionary processes that have left little signature in the genomes of living populations.
Orlando continues, “Ancient genomics has just rejected Botai as the ancestor of modern domestic animals. We are confident that ancient genomics will soon help identify the tempo and location of the domestication of horses. “
This is an important area of research, given that the domestication of the horse is one of the major transformative changes that have revolutionized human history.
Horseback riding has allowed us to travel well above our own speed, spreading our genes, diseases and culture over vast geographic areas.
The development of the cavalry was also essential on the battlefield until the mechanization of weaponry. Many conquerors are considered exceptional horse masters, notes Orlando.
Perhaps the most famous are Alexander the Great and Genghis Kahn. Some of their horses, like Bucephalus, are no less legendary.
“Horse breeders have transformed the horse dramatically throughout history, especially over the past few centuries with the development of intensive selective breeding,” says Orlando.
“It is therefore almost impossible to reconstruct the early stages of horse domestication by examining the genome of modern horses. “
In recent work, his team reconstructed the genomes of Scythian horses and clearly established that the animal’s genome has been altered significantly over the past 2,000 years.
By targeting the Botai horses, the team aimed for a deeper time journey, 5,500 years ago.
“Sequencing the genomes of the first domestic horses would make it possible to catch evolution in the act when we first tamed wild horses. This would reveal the biological changes underlying the process of domestication of animals in the beginning, ”says Orlando.
However, the results were a remarkable ball of curve. Rather than being the source of modern domestic animals, the Botai horses appeared to be the direct ancestors of another group of horses that lived in Kazakhstan around 5,000 years ago and the Przewalski horses, long considered to be the last truly wild.
“Our findings literally upset current original population patterns of horses: what we used to understand as the last wild horse on earth is actually the descendant of the first domestic horses, who simply escaped the pressure. human and have gone wild in recent years. millennia, ”says Orlando.
The study takes advantage of the large genomic dataset produced to identify the genomic changes underlying this process of feralization.
One of these changes affects a variant of the TRPM1 gene involved in leopard spots, which was once present in Botai horses but was removed from Przwewalski’s horse gene pool. As such a variant is also associated with color blindness, it is likely that it could only have been maintained artificially by human breeders, but was quickly lost by natural selection after the horse went wild.
PhD student Charleen Gaunitz, who also worked on the study with the Orlando team, said: “Ironically, we believed that the endangered population of Przewalski’s horses should be preserved as the last wild horses in the world. planet. We now find that they must be preserved as the closest offspring of the first domestic horses. “