Domestication

Competing theories exist as to the time and place of initial domestication. The earliest evidence for the domestication of the horse comes from sites in Ukraine and Kazakhstan, dating to approximately 3,500–4,000 BCE.^[123] It is thought that the horse was completely domesticated by 3000 BCE, and by 2000 BCE there was a sharp increase in the number of horse bones found in human settlements in northwestern Europe, indicating the spread of domesticated horses throughout the continent.^[124]

The "Four Foundations" theory

Przewalski's Horse, the last surviving wild horse species

Modern DNA evidence suggests that domesticated horses evolved from multiple wild populations.^[125] Classification based on body types and conformation, absent the availability of DNA for research, suggest that there were roughly four basic wild prototypes, thought to have developed with adaptations to their environment prior to domestication. There are competing theories, some argue that the four prototypes were separate species or subspecies, while others suggest that the prototypes were physically different manifestations of the same species.^[126] These animals probably were able to crossbreed with each other, thus were not completely separate species. Other theories hold that there was only one wild species and all different body types were entirely a result of selective breeding after domestication.^[127]

Whether wild or developed during early domestication, under the four foundations theory, all types and breeds of horses are thought to have developed from the following base prototypes:

• The "Warmblood subspecies" or "Forest Horse" (once proposed as Equus ferus silvaticus, also called the Diluvial Horse), which evolved into a later variety sometimes called Equus ferus germanicus. This prototype may have contributed to the development of the warmblood horses of northern Europe, as well as older "heavy horses" such as the Ardennais.
• The "Draft" subspecies, a small, sturdy, heavyset animal with a heavy hair coat, arising in northern Europe, adapted to cold, damp climates, somewhat resembling today's Fjord horse and even the Shetland pony.
• The "Oriental" subspecies, (once proposed as Equus agilis) a taller, slim, refined and agile animal arising in western Asia, adapted to hot, dry climates, thought to be the progenitor of the modern Arabian horse and Akhal-Teke.
• The "Tarpan" subspecies: dun-colored, sturdy animal, the size of a large pony, adapted to the cold, dry climates of northern Asia, the predecessor to the Tarpan and Przewalski's Horse as well as the domesticated Mongolian horse.^[126]

Feral populations

Main article: Feral horse

Feral horses are born and live in the wild, but are descended from domesticated animals.^[110] Many populations of feral horses exist throughout the world.^[128][129] Studies of feral herds have provided useful insights into the behavior of prehistoric horses,^[130] as well as greater understanding of the instincts and behaviors that drive horses that live in domesticated conditions.^[131]

Breeds

Main articles: List of horse breeds, Horse breeding, and Selective breeding

Horse breeds are groups of horses with distinctive characteristics that are transmitted consistently to their offspring, such as conformation, color, performance ability, or disposition. These inherited traits are usually the result of a combination of natural crosses and artificial selection methods aimed at producing horses for specific tasks. Certain breeds are known for certain talents. For example, Standardbreds are known for their speed in harness racing. Some breeds have been developed through centuries of crossings with other breeds, while others, such as Tennessee Walking Horses and Morgans, developed from a single sire from which all current breed members descend. There are more than 300 horse breeds in the world today.^[132]

Origin of breeds

See also: Domestication of the horse

Modern horse breeds developed in response to a need for "form to function", the necessity to develop certain physical characteristics in order to perform a certain type of work.^[133] Thus, powerful but refined breeds such as the Andalusian or the Lusitano developed in the Iberian peninsula as riding horses that also had a great aptitude for dressage,^[133] while heavy draft horses such as the Clydesdale and the Shire developed out of a need to perform demanding farm work and pull heavy wagons.^[134] Ponies of all breeds originally developed mainly from the need for a working animal that could fulfill specific local draft and transportation needs while surviving in harsh environments. However, by the 20th century, many pony breeds had Arabian and other blood added to make a more refined pony suitable for riding.^[135] Other horse breeds developed specifically for light agricultural work, heavy and light carriage and road work, various equestrian disciplines, or simply as pets.^[136]

Purebreds and registries

Main articles: Breed registry and Purebred

Horses have been selectively bred since their domestication. Today, there are over 300 breeds of horses in the world. However, the concept of purebred bloodstock and a controlled, written breed registry only became of significant importance in modern times. Today, the standards for defining and registration of different breeds vary. Sometimes purebred horses are called Thoroughbreds, which is incorrect; "Thoroughbred" is a specific breed of horse, while a "purebred" is a horse (or any other animal) with a defined pedigree recognized by a breed registry.^[137]

An early example of people who practiced selective horse breeding were the Bedouin, who had a reputation for careful breeding practices, keeping extensive pedigrees of their Arabian horses and placing great value upon pure bloodlines.^[138] Though these pedigrees were originally transmitted via an oral tradition, written pedigrees of Arabian horses can be found that date to the 14th century.^[139] In the same period of the early Renaissance, the Carthusian monks of southern Spain bred horses and kept meticulous pedigrees of the best bloodstock; the lineage survives to this day in the Andalusian horse.^[140] One of the earliest formal registries was General Stud Book for Thoroughbreds, which began in 1791 and traced back to the Arabian stallions imported to England from the Middle East that became the foundation stallions for the breed.^[141]

Some breed registries have a closed stud book, where registration is based on pedigree, and no outside animals can gain admittance. For example, a registered Thoroughbred or Arabian must have two registered parents of the same breed.^[142][143] Other breeds have a partially closed stud book but still allow certain infusions from other breeds. For example, the modern Appaloosa must have at least one Appaloosa parent, but may also have a Quarter Horse, Thoroughbred, or Arabian parent so long as the offspring exhibits appropriate color characteristics.^[144] The Quarter Horse normally requires both parents to be registered Quarter Horses, but allows "Appendix" registration of horses with one Thoroughbred parent, and the horse may earn its way to full registration by completing certain performance requirements.^[145]

Others, such as most of the warmblood breeds used in sport horse disciplines, have open stud books to varying degrees. While pedigree is considered, outside bloodlines are admitted to the registry if the horses meet the set standard for the registry. These registries usually require a studbook selection process involving judging of an individual animal's quality, performance, and conformation before registration is finalized.^[146] A few "registries", particularly some color breed registries, are very open and will allow membership of all horses that meet limited criteria, such as coat color and species, regardless of pedigree or conformation.

Breed registries also differ as to their acceptance or rejection of breeding technology. For example, all Jockey Club Thoroughbred registries require that a registered Thoroughbred be a product of a natural mating, so called "live cover". A foal born of two Thoroughbred parents, but by means of artificial insemination or embryo transfer, cannot be registered in the Thoroughbred studbook.^[142] On the other hand, since the advent of DNA testing to verify parentage, most breed registries now allow artificial insemination (AI), embryo transfer (ET), or both. The high value of stallions has helped with the acceptance of these techniques because they allow a stallion to breed more mares with each "collection", and greatly reduce the risk of injury during mating.^[149] Cloning of horses is highly controversial, and at the present time most mainstream breed registries will not accept cloned horses, though several cloned horses and mules have been produced.