As with so many details of history, we'll probably never know; human and horse history entwine at a point too far back from us for us to point it out with any accuracy. Breeding may begin as far back as 4500 BCE; evidence from around that period suggests the beginning of horse domestication in the Eurasian steppes of 4000 BCE.

In that rough, cold, open environment (centered on what is now Ukraine), archaeologists find evidence of the use of bits in the 6000-year-old remains of horse teeth. (Other evidence from this era and area includes the appearance of horse bones in human graves - apparently cowboys weren't the first to insist on being buried with their loyal steeds.)

But we don't find much direct evidence of horse breeding (as opposed to possible domestication) until much later, with the rise of the Bedouin culture of the Middle East. Before they began issuing written documentations of horse pedigree, around 1330 CE, they transmitted such information via oral tradition - for how long we don't know, but possibly for thousands of years. Farther east we have the Akhal-Teke of West-Central Asia, who bred horses for war and racing, as did Mongolian nomads from time immemorial.

Cultures bred - and breed - horses for a variety of purposes, and breed them, accordingly, for a variety of qualities: speed (for messaging or racing), size (for mining), heft (for plowing and wagon-pulling), smoothness of stride (for riding). In medieval-era Muslim countries, war horses were bred for speed and agility, which allowed for a more flexible army; Europeans, who'd bred their steeds by contrast for the greatest possible size (so they could carry armor long distances, and so they could power devastating lance thrusts). When the two cultures clashed - for example, during the Crusades - the lumbering brutes of the European armies found themselves outflanked and outmaneuvered, like Hummers beset by armored motorcycles.

The Europeans, learning from their mistakes, bred a new kind of horse - a sampler-platter of both species' strengths, bred from captured Arabian horses to combine nimbleness with strength. (One of the horse strains resulting from this early genetic experimentation was the Courser, a predecessor to the Thoroughbred.)

Leave it to the nobility to make a fashion out of what was a matter of life or death to others: European elites of the Renaissance period bred special horses designed to do warhorse's military maneuvers with a maximum of picturesque grace. The development of gunpowder also changed the way horses were bred during this period, increasing the need for quicker, more Arabian-style war horses to enable the brave cavalry of lionhearted England to shoot, run, and hide.

The reintroduction of horse racing to England - banned by Cromwell after the Puritan rebellion of the 1640s, and restored, along with the monarchy, in 1660 - led to the development of the Thoroughbred horse, descended from three strains of Arabian stallion, around 1700.

In the new century, an important one for the history of horse racing and race horse breeding, an English nobleman named James Burnett (Lord Monboddo) worked out one of the first treatises on the theory of horse breeding, an enquiry which led him to consider the evolution of species more broadly. The development of this field of science gave European biology a shot in the arm - and, alas, encouraged also the development of specious racial and hereditarian theories, which did nothing to advance science but quite a bit to give racists and snobs an excuse for their prejudices. (Think of the population theorist and Darwin influence T.R. Malthus, with his desire that "inferior" poor people starve so that they might be prevented from breeding.) People, unlike racehorses, can't be bred for perfection, as such modern boondoggles as the Nobel Prize Sperm Bank have made clear. (Even with racehorses, it's never been an exact science.)

Over the next two centuries, a need for carriage horses drove the breeding of warm blood horses - adaptable, smooth-riding horses who continue to dominate today's show-jumping arenas.