Changes in the horse brought about by domestication
It is difficult to know which changes in an animal species are due to domestication, per se, and which are simply due to natural selection or genetic drift. In the following, I do my best to contrast today’s horses with pre-domestication horses, horses from about 500 years ago, and horses from about 50 years ago. Early horses were bay or dun in color and between 12 and 14 hands tall (48 and 56 inches at the withers) (Clutton-Brock, 1992). This size is similar to that of the Przewalski’s horse and the zebra. In contrast, today’s domestic horse is widespread geographically and exhibits broad phenotypic variation. The tallest horses may be 20hh (80 inches at the withers) and the smallest may be just 6hh (30 inches). There are at least 395 horse breeds, which fall generally into three types. Draft horses are large, heavy-boned animals, developed in Northern Europe for work like pulling and plowing. Light horses are finer-boned animals used for riding and harness work. They can generally trace back to the Arabian horse. Ponies are shorter animals which were developed in harsh conditions in which a larger animal would not be viable (Splan, 2005). Overall, over the last few thousand years, horses have become much more varied both phenotypically and genotypically. Different individuals can complete a wide variety of tasks, including pulling heavy loads, sprinting up to 40 miles/hour, and kindly tolerating small children.
Although there is evidence that horse shoes and stirrups were accepted as long ago as over 1000 years in western Europe (Clutton-Brock, 1992), it was over the last 500 years that specific types of horses and specific styles of riding emerged. Dressage-style riding originated as a style of riding used by cavalry soldiers to train their warhorses. At the end of the 16th century, Antione de Pluvinel founded a riding academy originally intended to train soldiers. However, much of the riding was done in time to music and involved the very careful and precise movements associated with dressage today (van Orden, 2005). In the United Kingdom, huntseat style riding appeared in the 18th century, a very different style than the European Dressage style that had been prevalent. Huntseat style allowed riders to sit more forward, with shorter stirrups, and allow their horses more freedom of movement and speed (Raber and Tucker, 2005).
Of particular note is the fact that during this time, horses were re-introduced to the Americas, this time as domesticates instead of a wild predecessor of the horse. Some tribes of native people in both North and South America developed cultures around horses (as discussed elsewhere in this project, particularly with regard to the appaloosa). They had to re-invent the wheel, more or less, in terms of riding, but were able to do so, very successfully. Western (cowboy) style riding also appeared in the Americas and became prevalent (Clutton-Brock, 1992).
Varying types of horses emerged as well. The appearance of the larger, heavier horse in England is attributed, in part, to King Henry VIII, who required in 1535 that “all substantial land owners must keep at least two mares over 13hh” (52 inches at the withers or shoulder) (Clutton Brock, 1992). Later, in 1541, he outlawed the “grazing of stallions under 15hh (60 inches at the withers or shoulder) on common land” in some parts of England. Following this initial effort, until the 1800s, the heavy draft-type horse was very popular and was used for riding and for pulling carriages. Only in the 17th century did today’s light horse appear—looking more like what we now call the hunter-type horse (Clutton Brock, 1992).
Over the last 50 years, horses have become much more specialized and have become something of a commodity or companion-type animal. They are no longer working animals in most situations; rather they are pets or top-of-the line performers and athletes. There are horses bred specifically for one task: some are jumpers, others are children’s mounts, still others perform in fancy shows. Horses no longer work for a living—they are not required by anyone for transport or labor. Rather, they, like dogs and cats, are something that people keep purely for entertainment, while machines now do the hard work that horses used to do (transportation, farm work, etc). This, interestingly, is similar to the use of horses by ancient Egyptians, for whom horses were a sign of great wealth owned only by the upper class (Clutton-Brock, 2012); donkeys were used for hard work.
In part as a result of horses becoming a companion and commodity-type animal, in the United States, horses have increasingly been divided into specific breeds, based on appearance, attributes, or color, with breed associations that register horses and hold competitions open only to those registered with the association. Breeds in the United States are generally closed to individuals outside the breed (that is, only the offspring of two registered Quarter Horses can be registered with the American Quarter Horse Association). Horses are selectively bred to have certain traits that will make them competitive in the show ring. These traits are sometimes related to athletic ability, but other times are arbitrary, stylized, and very exaggerated (Borneman, 1988). John Borneman gives the example of the Quarter Horse hindquarters—initially having strong, well-muscled hindquarters was a useful trait, as it made Quarter Horses faster. However, this trait was desired in the conformation classes in horse shows and thus was selected for by breeders. An exaggerated, overly muscled hip appeared and was not desirous for riders—it makes the horse a rougher ride. This means, basically, that some Quarter Horses were actually being bred in such a way that they were worse riding horses than their predecessors (1988). Similarly, in Quarter Horse western pleasure classes, classes in which the horse’s gaits and manners are judged while the horse is ridden at the walk, trot, and canter in western-style tack, horses with a very slow and quiet way of going were rewarded by judges. Then, horse trainers began asking their horses to slow down more and breeders began selecting for the horses that moved slowly (referring to this trait as being “slow-legged”). Now, in western pleasure classes, horses move in highly stylized and almost unnaturally slow gaits. While these gaits win in western pleasure classes, they do not have any functional purpose.
This is a picture of a Quarter Horse that is heavily muscled with a large, well-muscled hindquarter.
This is a picture of a very slow-going western Quarter Horse.
Rodeo—an event in which cowboys (or girls) and horses compete in a variety of events—emerged in the last 100 years or so. While it originated as a way for cowboys and their horses to show off their skills working cattle—which had a practical use—it is now simply another competition, because mounted cowboys rarely actually work cattle (Anonymous, 1996). Over the last 50 years, horses have lost their functional purpose and shifted to entertainment and commodity purposes.
Interesting related note (about Norwegian Fjord horses)
The Norwegian Fjord horse still possesses many primitive characteristics today, in terms of its physical phenotype. It is roughly the same size and color as the early horses and is very cold-hardy, as they were. However, its temperament is very docile and tractable, to the point of almost being insensitive, in some cases. The Norwegian Fjord Horse Registry claims that Norwegian Fjords were domesticated separately from other breeds of horses, in Norway, about 4000 years ago (http://www.nfhr.com/). A recent study of genetic similarity of various horse breeds also supports this—it found that the Przewalski’s Horse (the last remaining wild horse, presumably fairly genetically similar to the wild predecessor of the domestic horse) is genetically much more similar to the Norwegian Fjord than most horse breeds are (McCue et al., 2012) (linked figure from McCue paper shows graphically genetic relatedness).
This evidence is not conclusive enough to definitively state that Norwegian fjords were indeed domesticated separately from other breeds of horses. However, it indicates that they are indeed more primitive and more similar to true wild horses than most breeds are.
This is a picture of four Norwegian Fjords (with whom I’m personally acquainted), with the typical primitive characteristics—stripes on legs, dorsal stripe, dun color, relatively small size, etc.