The horse, its four slender legs accomplishing astonishing feats of strength and endurance, has provided humans with far more than transportation from point A to point B.
It has allowed us to travel long distances for trade, carry heavy loads, move our societies around more freely and, inevitably, conduct more efficient warfare. Arguably the most important domesticated animal, the horse also has provided humans with meat and milk.
Now we have a better idea of when this complex and vital human-horse relationship began.
New evidence, including more slender leg bones, bit-pitted teeth and mares milk residue in pottery, indicate that the horse was domesticated on the steppes of Central Asia at least 5,500 years ago, more than 1,000 years earlier than previously believed and 2,000 years before it appeared in Europe.
"To me, the domestication of the horse was a seminal event in human history," said archaeologist Sandra L. Olsen of the Carnegie Museum of Natural History, a co-author of the paper appearing today in the journal Science. "All the major empire builders, like Alexander the Great and Genghis Khan, would have been nothing without horses."
It was believed that the oldest evidence of domestication was found at the village of Dereivka in Ukraine, dating to about 2000 BC. But Olsen and some other researchers argued that domestication occurred much earlier among members of the Botai culture on the steppes of what is now northern Kazakhstan.
She and her colleagues found a variety of evidence suggesting domestication, including a horse corral, the use of horse manure in roofing materials and the widespread use of rawhide tools such as lassos, which are generally associated with horse-dependent cultures.
That evidence has been controversial, with critics suggesting that it may only represent exploitation of feral horses.
But the new finds "make it fairly unambiguous that this early Botai site had domestication," said archaeologist Alan K. Outram of the University of Exeter in Britain, lead author of the paper. The fact that the Botai people were both milking and riding the horses, he said, indicates "a full pastoral economy, which suggests that there are even earlier domesticated horses to be found."
Archaeologist David W. Anthony of Hartwick College in Oneonta, N.Y., a leading expert on the domestication of horses, agreed in an e-mail message, calling the identification of mares milk residue in the pottery "a spectacular and brilliant advance. . . . If you are milking horses, they are not wild!"
Botai was a village on the banks of the Iman-Burluk River, a tributary of the Ishim, in Central Asia, west of China and south of Russia. The site was occupied from about 3700 BC to 3100 BC.
The country is flat and dry with vast steppes, or wide-open spaces. It also has extremely cold winters, much too cold for early people to have depended on conventional domestic animals, which must be sheltered and fed in winter.
Horses, in contrast, can survive in the cold and can forage even in snow.
The village of about 1,000 people had about 150 pit houses sunk into the ground to provide insulation, said Olsen, who has been working there since 1993.
In the village's middens, 90% to 99% of the bones are horse, indicating residents' extensive reliance on the animals. The Botai people could not have maintained such a large settlement if they were relying only on hunting wild horses on foot, Olsen said, because they would have quickly depleted the horse population around them.
The researchers had suspected that the Botai people had domesticated horses, she said, "but this clinches it."
Analyzing bones from the middens, the team discovered that the lower leg bones, or metapodials, of the horses from the site were more slender than those of wild horses and similar in size to those of later domesticated horses, a trait selected by breeders for speed.
Another part of the research, developed by Outram, was the analysis of pottery to reveal the presence of lipids (fats) characteristic of horses. Mares milk is still consumed in Kazakhstan and is usually fermented into a slightly alcoholic drink called koumiss. This study, Outram said, shows that the practice dates to the very earliest horse herders.
Using a new technique developed by co-author Robin Bendrey of the University of Winchester in Britain, the researchers also identified damage to the horses' teeth, which indicated the use of a bit -- meaning the animals were ridden.
This is the weakest part of the study, Anthony said, because the damage to teeth is "preliminary and somewhat speculative." He said that aspect of the research would need to be replicated before he and others would fully accept it.
"It is not so much the domestication of the horse that is historically important, but the invention of horseback riding. . . . When people began to ride, it revolutionized human transport," he said, and with that came other developments that changed the world forever.