Horses could be considered man's best friend.
Horses were able to transport people and their goods. They revolutionized warfare by drawing chariots and carrying the cavalry. They have inspired artists from Stone Age cave painters, to the creators of "My Little Pony," and although their role in industry has diminished, they continue to be a part of our sport, leisure, and collective hearts. Since at least 2000 B.C.E., horses have been closely linked to human culture. Associated with some human groups even earlier.
Ludovic Orlando, molecular archaeologist at University of Toulouse III-Paul Sabatier (France), says that horses are "the animal that changed history."
Horse breeds today number in the hundreds. They range from the Lipizzan horses of Austria, to the Clydesdale draft horses used in Budweiser ads, to the thoroughbreds of Kentucky Derby. These animals, despite their differences, are Equus caballus. They are joined in the modern Equus family by donkeys (pronounced shuhVAL-skees), zebras, and wild Przewalski’s horses (pronounced “shuh-VALskees”) of Central Asia. Taxonomists prefer Equus ferus for wild horses. Przewalski’s horses classifications can differ.
The evolution that led to Equus is a classic example of evolution. It's a well-documented history that graces museum exhibits and textbooks. The path to domestication of horses by humans has been obscured until recently. E. caballus' bones look almost identical, wild or domestic. This makes it difficult to answer the long-standing question: When and where did humans first domesticate horses?
The study of DNA from ancient and modern animals is undergoing a revolution that provides answers. Scientists have discovered much about Equus caballus' history using the same method used in the landmark 2010 study on Neanderthal DNA. They discovered the fascinating history of Przewalski’s horse by studying how wild horses used the Bering Strait to share genes with humans in North America and Asia. They also examined more recent samples and discovered that modern management has resulted in a lot of horse genetic diversity being lost, as well as a variety of breed-specific characteristics.
However, there has not been enough ancient DNA to answer this question -- that is until the late 2021 when scientists published their analysis of over 250 ancient horse genomes.
Jessica Petersen (an animal geneticist at University of Nebraska-Lincoln) says that it's great to have the big puzzle of where horses came from solved. She adds that the process of domestication was complex and will take time to unravel.
Paleontologists have been able to trace the ancestry and evolution of horses through fossil bones and teeth. They found evidence that the horse genus Equus was formed between 4 and 4.5 millions years ago on the continent that would become North America. This was well before the Homo lineage which would not appear on the scene for at most a million years.
Now, it's the Pleistocene (11,700-129,000 years ago), when horses were trotting back and forth on the Bering Land Bridge between Asia and Americas. Between 35,000 and 50.000 years ago, the line that led to domestic horses and wild Przewalski horses split.
The Bering Land Bridge was submerged for its last time around 11,000 years ago. This is when the North American horses disappeared along with other large species like mammoths or giant beavers. Although it is difficult to determine the cause, Alisa Vershinina, who was a researcher at University of California, Santa Cruz, investigated the Bering crossings and suggested that climate, hunting, or a combination of both could have played a role.
Horses were a common sight among early humans. They are also the most prominent animal depicted in cave art from Western Europe and Stone Age. There is a huge difference between watching horses for artistic inspiration and using them to power, transport, and sport. What happened to the relationship between man and beast?
The barnyard was only recently expanded with the addition of horses. Dogs were domesticated 15,000 year ago. Sheep, pigs, and cattle were domesticated between 8,000 and 11,000 years ago. However, there is no evidence that horse domestication was ever documented in the archaeological records until around 5,500 years ago.
Scientists have several options for the first domestication event, as they had many horse remains from Eurasia. One example is the 2018 discovery of a frozen and mummified horse in Siberia. It was found to be approximately 4,600 years old. Could it have been one the first workhorses to emerge?
Iberia, the peninsula that includes modern-day Spain or Portugal, looked promising, as horses have inhabited the area for over 50,000 years and were therefore likely to be available for domestication.
Archaeologists found horse remains in Eastern Europe, near the Caspian Sea. Some human burials containing maces with horse heads were found around 6,000 years ago. This could indicate a change in human-horse relationships. The area was also well-known for its long-standing horse presence.
The 3500 B.C.E. archaeological site was what captured the attention of many horse-domestication experts. Botai is located approximately 1,000 miles north of the Caspian. It's now part of Kazakhstan.
According to Alan Outram, a University of Exeter zooarchaeologist, Botai's diet was "entirely concentrated on horses." Other than a few bones from dogs, the majority of the non-human remains found on the site are horses'. Evidence is found of fenced yards which might have been used to house herds. Some skulls suggest that horses were killed with an ax-like tool. Horse teeth show "bit wear" as if they had been bridled. Outram believes that pottery shards may contain chemical traces mare's milk. This could have been used as butter, yogurt, or cheese.
However, it is still highly debated about the importance of this site. It is not possible to prove that Botai residents had ever domesticated horses. Outram believes that Botai peoples treated horses in a similar way to modern reindeer herders. They might have kept horses close at hand to provide meat or milk and may have even ridden some horses to help others. They probably didn't manage breeding the animals or use them extensively as pack or transportation animals.
Without enough ancient DNA, it was impossible to know if these horses were human-managed animals.
Orlando, Outram, and their colleagues then analysed a wide range of horse genomes. They covered a period from 42,800 years ago to the present day, including 18 modern breeds. The findings were published in Science in 2018. The results: Today's draft horses, ponies and other animals have very little in common with Botai horse bones. Outram says, "They are not the genetic origin of modern domestic horses."
However, the Botai lineage continues to exist. The researchers were able, unexpectedly, to draw a line between the 5,500-year old bones and the modern Przewalski horses. These large, stocky animals have short, bristly hair and live in Mongolia's steppes. They are considered a national symbol because of their unique appearance.
Przewalski's horses may no longer be considered wild, despite being once thought to be the last remnants of an ever-wild population. They are likely to be the wild descendants of horses Botai may have managed to some degree but lost control over. This would be similar to other feral populations, such as the Australian brumbies and mustangs from the American West.
Przewalski's horses don't make good riders, according to Arne Ludwig (German evolutionary geneticist, Leibniz Institute for Zoo and Wildlife Research). He speculates that this could be why they have fallen out of favor.
No matter what happened, Przewalski's horses were a tough bunch. The last wild animal disappeared in 1969, and they almost went extinct. The current population is made up of descendants of only a few animals that survived in captivity. There are currently around 2,000 individuals either in natural reserves or captivity. A few domestic horses are also included in the family tree.
These advances aside, Orlando, who documented genomic studies of horse breeding for the Annual Review of Genetics 2020, was forced to conclude that "The geographical origin of modern domestic horses" is not known.
The clues were growing. Scientists had already rejected the Siberia and Iberia candidates. Researchers looked at ancient DNA to discover that these horse populations were declining, which was a significant contribution to modern domestic lineage.
Orlando, the lead author of this paper says that it was a numbers game to find the true site for domestication. "We constructed the answer by narrowing the evidence, little-by-little." More than 150 scientists, including Outram, Ludwig and others, continued adding horse genomes from Eurasia, spanning approximately 50,000 to 200 B.C.E.
With 264 ancient horse genomes at hand, the answer was obvious: The home of modern domestic horses was the region of Western Eurasia north of the Black sea and the Caspian Seas. This area is also known as the Lower Volga Don region. In October 2021, the team published their findings in Nature.
Although the data points to a clear answer there is still much room for interpretation and speculation. It's possible that horses were bred in a spot near the Caspian, but it doesn't necessarily mean that this was the only time. Evidence from other candidate areas suggests that horses were domesticated at Botai multiple times without leading to widespread horsemanship.
Beth Shapiro, an evolutionary biologist from the University of California Santa Cruz and coauthor of the Nature study, said, "It shows just how important horses were for people. That so many people independently domesticated them."
The analysis of 2021 suggests that domestication in Volga-Don was "the only one," and the only one to spread like wildfire horse-drawn. What was the reason horses were one of the last domesticated animals? And why specifically these horses?
Although it is impossible to know for sure, ancient genomes offer intriguing hypotheses. GSDMC was a gene that changed the lineage of modern domestic horses. People often have back problems when their genes are altered. It is possible that domestic horses gave animals stronger backs which made them suitable for long-distance riding.
A ZFPM1 gene is also present in the domestic horse line. This gene is essential for mood regulation. Maybe ZFPM1 was domesticated and made the animals more docile and easier to handle. These changes may have been key to long-term horse breeding, but it's speculation.
Orlando says it is impossible to pinpoint the origins of domestication. It is possible that several people from the region experimented with horses around 4,200 years ago. Although domestic horses did spread from then on, it wasn't until 2000 B.C.E that things really took off.
Scientists tentatively attribute the explosive growth in horse-based transportation and technology to the warlike Sintashta cultural, which lived on the north Eurasian steppes from 2100 to 1800 B.C.E. Outram claims that the Sintashta traveled between Asia and Europe and, presumably, picked up horses during one of these trips. Later they rode or used the horse-drawn carriages that were found in their graves.
This was in the Bronze Age. It is believed that horses were used to transport people from the steppes, as well as cultural accessories such advanced metalworking, lightweight spoked wheel and Indo-European language. In a book titled "The Horse, the Wheel, and Language", David W. Anthony, an American Anthropologist, suggested that steppe dwellers created the spoked wheel to make their horses more useful in transporting cargo and for chariot-based warfare. These elements of steppe culture and the Proto-Indo-European language would have been helped to spread by the prestige of horses and metal goods.
This resulted in horsepower and spoked-wheels becoming commonplace over the centuries. Languages such as Welsh, Polish, and Punjabi can all be traced back at the same root.
The domestication of horses was only the beginning of a relationship between humans and them, and between humans and their DNA. Over millennia, human management can make a remarkable impact on the animal genomes.
All modern domestic horses have almost identical Y chromosomes, even though they are only passed through the male line. Ludwig, Orlando, and their colleagues examined the Y chromosomes from 96 Eurasian stallions over the past 5,000 year to see how it happened. Although Y chromosomes were initially quite diverse, they began to become more similar over time. The first big changes occurred around 1,500 years ago. Orlando says this is when some bloodlines like the Oriental horses became popular for breeding.
Even this level of breeding is still quite mild in comparison to what has happened over the past 200 years. Even though specific breeds have acquired the genes that give them their distinctive characteristics, the diversity of horse genetics has declined further.
Petersen of the University of Nebraska-Lincoln has been studying modern breeds to find regions of their genome that are associated with color, speed and gait. In racing breeds like thoroughbreds, for example, it is known that there are changes in the gene for muscle protein myostatin. Petersen also considered "gaited breeds", which have unusual locomotion styles, or in her words "horses who move funny", and are more comfortable to ride. These breeds often have DNA changes in one spot that act as a "master switch" for their gait. This spot is home to a gene called DMRT3 and a shortened version thereof has been linked with horse gait. Mice lacking this gene have issues with their spinal nerve function.
Orlando, who began riding lessons in 2019 despite his differences, believes there is something special about the horse-human relationship.
He says, "You get the feeling that the animal understands you when you ride it." You also feel empowered when you master this large animal.
How could humans resist this opportunity to make horses their best friend in war and peace, as well as for work and pleasure? It was a match made in heaven.
