The horse in history, a thundering success

If you were asked to name the most important domesticated animal, which would you choose? Perhaps, to play for time to consider it a bit, you might not immediately answer but ask “most important by what criterion?” That would be a good move. The different domesticated animals have played very different roles in human life and it is hard, if not impossible, to decide which was the most important in a general way. Hence, let us narrow the question and ask specifically, which domesticated animal was the most important in influencing human history?

Let’s see: it would probably not be the house cat. Many millions of cats have been deeply loved by their owners and have been important in that way. Yet, while there are stories of famous people and their cats, I do not know of examples of cat-human relationships that had any influence on specific historical events. (Any readers who know of such, please tell me in the Comments.) What about dogs? In addition to their role as humans’ best friend, dogs have been employed as helpers in far more ways than cats. (Think of the different kinds of dogs used in hunting, such as foxhounds versus retrievers, or the different breeds used in shepherding or guarding animals.) Again, however, it would be difficult to argue that human history would have been dramatically different if wolves had not evolved into dogs 20 to 30,000 years ago to become our most faithful animal companion. (See Animal Domestication: A relatively recent but transforming event in human history.)

Other popular domesticated animals, such as pet mice or rats or rabbits similarly fail the history-changing criterion. Of course, to take quite different animals, there have been those that have supplied major staples in the human diet, in particular cattle (both meat and milk) and chickens (for meat and eggs). Thus, in supporting the growth of human societies, they have been very important but in a raher diffuse, long-term manner rather than in influencing specific events.

For me, the answer to the question of the most important animal historically is “the horse”. Indeed, I would say it wins hands down or should I say “hooves down”. The reason is that the whole history of Asia and of Europe in the last three thousand years involved the massive movements of men on horseback as warriors and raiders. The horse was integral to those events. There could not have been equivalent movements of men on foot. Hence, human history in the greatest landmass on Earth, Eurasia, would have been radically different had the horse not been drafted into human service. Later, the horse would play a big role, if not on the scale of the earlier story in Asia, in the unfolding of history in North and South America.

This saga of the horse as warhorse initially seems like just a matter of history. However, it is also a story of biology, specifically of what changes in horse biology made it possible for horses to assume their role in warfare. It involved several crucial genetic changes in the horse, which have recently been coming to light. We discuss them shortly.

The details of the fascinating historical story of the horse as a major player in the history of Eurasia are recounted in a recently published history titled “Raiders, Rulers, and Traders” (RRT)¹ Of course, most people know of the Mongolia ruler, Genghis Khan (original name: Temüjin), who built up his horse-mounted warrior army in the early 13^th century CE (Current Era) to be the largest marauding force in history. At times it amounted to more than a million men and more than a million horses, who swept across Asia and much of central Europe, toppling many rulers, over a 20 year period to create the largest empire ever.

Yet, as RRT discusses and explores, the story of the horse in war began about 17 centuries earlier, with the ancient Persians, who used horses to drive chariots, especially in war. This began long before there were mounted cavalry troops. Chariot-driving lasted into the early days of the Roman Empire. By then, however, people had long been mounting horses and riding them.

During the roughly 1200 years between the start of the Roman Empire and the rise of Genghis Khan, however, there was a huge development of armies of men riding on horseback. This required, in turn, tremendous development of horse breeding and horse training. This took place initially and for centuries afterwards in central Asia on the steppes, the huge grass covered flatlands, covering 3.1 million square miles or about 7% of the surface of the land on Earth. The horse had evolved to eat grass and needed lots of it.² The steppes were the perfect environment for the horse. It is no coincidence that the great use that Native Americans put the horse to in later centuries was especially apparent on the American equivalent of the Asian steppes, namely the Great Plains.

At first, the raids and the conquests in Eurasia took place relatively close to home of the raiders but as the multiple skill sets required (for looking after the animals and for riding and fighting from horseback) developed and spread, the campaigns across the steppes went over longer and longer distances. These military campaigns reached China and India and of course all the places in-between where there was adequate grassy steppe land for the horses. An interesting aspect of this whole phenomenon was that horses made all this possible but, at the same time, the requirements for feeding horses demanded control of immense amounts of grass, which meant that the armies had to stay on the move, to allow the grasses to grow out again after intense grazing by the horses. The horse thus allowed the building of these empires but its needs en masse necessitated maintenance of control of large swathes of grassland.³

In fact, every story of animal domestication is a two way street, involving a long series of reciprocal interactions. First, humans start by domesticating the animals. However, fulfilling the basic needs of the animal starts shaping the lives of the people tending the animals. The greater the number of animals, the greater is their impact on the people keeping them. The story of the horse is a particularly dramatic example of this process because of the way the horse shaped the political landscape over a vast area for about two thousand years.

And over time, centuries to millennia, genetic changes take place in both the animals and the people. Those appearing in the animal are usually more obvious, often resulting in changes of the body or coloration, while those that take place in the people are more hidden, being physiological and (hypothetically) behavioral. The physiological changes in the humans often involve diet – digesting the meat or the milk of the animal – while the behavioral ones are still largely conjectural, probably involving changes predisposing toward better handling of the animals.⁴

It is beginning to be possible to say something about the genetic changes that took place during the domestication of the horse. A starting point for any such discussion is that there is general agreement now that horse domestication first began in Central Asia, somewhere between 5500 and 4000 years ago. The region believed to be the initial site of horse domestication is Northern Kazahkstan and the people who first carried it out are the local people termed the Botai. However, another possible first site is the region of the Pontic Steppe, north of the Caspian and Black Seas.

The first direct riding of horses probably occurred in either of those sites but there are no written records and there is relatively little in the archeological record. The main evidence for early horseback riding is from horse skeletons from that time, some of which show osteological injuries consistent with the animals having had riders.

The reasons for the domestication of the horse are obscure. They may have been used for herding cattle and sheep, whose domestication had long preceded that of the horse. In addition, horses were almost certainly a source of meat and both wild and domesticated horses were undoubtedly used this way. Cattle and sheep were already good sources of meat but given the reliance of horses on grass as their main food staple, they may have been easier to keep alive than cattle and sheep, whose food requirements were more demanding. Possibly in these early times, but certainly later in history for many peoples of the steppes, horses were also a source of the very nutritious milk that mares produce.⁵

Genomic research is now adding considerable understanding to our picture of the evolution of the horse under domestication. This has involved, in particular, the analysis of DNA from bone specimens thousands of years old, so called ancient DNA analysis. If the bone samples can be dated accurately, and they usually can be, using carbon dating, one can determine from the DNA extracted from it whether a genetic change had occurred by that time. Furthermore, if there are multiple samples from different animals, one can determine approximately how wide spread the change had been. Furthermore, if the biological function of the DNA sequence is understood, one can reconstruct at least a plausible explanation of what the consequences of the change had been. The DNA analysis can also provide strong evidence as to whether the sequence change had been positively selected from what is called a “signature of selection”.

A recent study of ancient horse DNA has brought to light two genetic changes of note that illuminate the process of horse domestication. The analysis focused on the horse lineage termed DOM2, which originated in the steppe Don-Volga region and is believed to be the one that gave rise to all the domesticated horses we have today.

Of the two genes highlighted in the study, one is a gene called ZFPMI. The variant that increased strongly did so in early domesticated horse populations starting from about 4000-5000 years ago. From mouse studies, loss-of-function (l-o-f) variants of this gene (for explanation, see Should genes be seen as controllers or nudgers of biological development?) are known to be associated with increased anxiety and fears associated with certain situations. The interpretation is that an early step of domestication involved selection for the variant identified in the bone samples which would have decreased anxiety and fear. This would have made it easier for horses to be near humans with less fear, facilitating their domestication. There, of course, might have been other genetic variants involved as well but this is highly likely to be one source of an increased threshold for the fight-or-flight response, which would facilitate domestication.

The other gene identified in this study is designated GSDMC. Other work had already implicated this gene in horses as playing a role in body conformation, particularly the spine. L-o-f mutations in mice show that such variants of this gene can effect not only the spine but forelimb strength and locomotor abilities. From the analysis, it seems that the allele that characterizes modern horses began to rise from about 4200 years ago. This corresponds to the approximate time that people may have started riding horses. The inference is that this allele helped give horses extra back strength, to allow them to bear the weight of a human body, and quite possibly other traits that improved their speed or other aspects of their locomotion. If so, this change would have allowed the horse to be adapted more than a thousand years later as an animal able to participate in war.⁶

These findings are undoubtedly only the beginning of our understanding of the genetic characteristics of the horse that allowed it to become the special domesticated animal it is but they are a strong start. In a future article, I will return to the horse to describe its unusual psychological and social features that make it the special animal that it is.

1. See David Chaffetz (2024) Raiders, Rulers and Traders: The horse and the rise of Empires London: W.W. Norton and Co. For those who do not have time to read the book, I recommend a delightful review: Doniger, W. (2025). The rise and fall of warhorses. The New York Review of Books, 10 April, 2025, pp. 17-19.

2. The remote ancestors of the horse were not grazers, living on grass. The progenitor of the horse family, Eohippus, was a fox-size animal that lived in the forest and was a browser, eating leaves; it lived about 55 million years ago. It gave rise to descendants that over time, and with many changes in climate, were larger, had fewer toes, and were becoming grazers, with higher-crowned teeth. By about 20 million years ago, there were members of the horse family that were undeniably horse-like in shape. Horse evolution was once thought to be a kind of straight line, with one more “advanced” form replacing the previous one. Now we know from a much fuller fossil record that it was an evolutionary “ bush”, with many branches (different forms existing at the same time), just as we now see human evolution. The genus Equus, the sole surviving horse genus, evolved about 4 to 4.5 million years ago. It contains the horse, zebras and asses.

3. For particularly good discussion of this point, see chapters 2, 3, and 8 in RRT.

4. It is just an inference that long contact by humans over generations with an animal that brings us benefits, caring for its needs, might select for certain behavioral traits in the people doing the tending, but that fits with everything we know about evolution and the power of selection. We humans, for instance, have almost certainly become more domesticated ourselves in our interactions with one another since our species first arose. At some point, when we know more about the human genome, and which genetic variants of which genes are associated with which traits, we will be able to investigate this possibility, using comparisons with ancient human DNA samples from humans who lived before there was animal domestication.

5. For this aspect of horse history, see Chapter 1 of RRT and for a good overview of domesticated horse history, see chapter 11 of R.C. Francis (2015). Domesticated: Evolution in a man-made world. London: W.W. Norton and Co.

6. For the research article that describes this work in a lot more detail, see X. Liu et al. (2025). Selection at the GSDMC locus and its implications for human mobility. Science 28 August, 2025, pp. 925-930.