The Botai of central Asia milked mares more than 5,000 years ago: hunter-gatherers left signs of domesticated horses.

Central Asia's vast grasslands hosted a prehistoric revolution in transportation, communication and warfare, thanks to the humble horse. Remains from Kazakhstan's more than 5,000-year-old Botai culture have yielded the earliest direct evidence for domestication of this versatile beast, scientists report.

Botai people were hunter-gatherers who lived in large settlements for months or years. Their culture lasted from 5,600 to 5,100 years ago. Researchers have long suspected that the Botai rode domesticated horses while hunting for wild horses to eat but did not domesticate other animals or cultivate crops.

Horse remains found at four Botai sites include two telltale signs of domestication: slender lower-leg bones like those of later domesticated horses and cheek teeth worn down by bits that attached to bridles or similar restraints, reports a team led by Alan Outram of the University of Exeter in England.

Chemical analyses of animal fat residue on the inside surfaces of Botal pottery fragments suggest that the vessels once held mare's milk, probably gathered in summer months, the researchers report in the March 6 Science. Modern Kazakh horse herders milk mares in the summer to produce a fermented, alcoholic drink called koumiss.

Milking of horses and other animals arose in areas such as northern Kazakhstan that lacked agricultural practices often regarded as precursors of milking, Outram and his colleagues propose.

The new report presents the first evidence for horse milk in Botai pots and for Botai horses having domesticated-looking leg bones, remark David Anthony and Dorcas Brown, archaeologists who teach at Hartwick College in Oneonta, N.Y.

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"If you're milking horses, they are not wild," Anthony says.

But the evidence for bit use described by Outram's team is preliminary, according to Anthony and Brown.

The Botai people didn't invent horse domestication and milking, Anthony and Brown contend. These practices were probably borrowed from inhabitants of the nearby Russian steppes who may have included domesticated horses in sacrificial rituals with domesticated sheep and cattle by 6,500 years ago. Those Botai neighbors probably domesticated horses after learning about cattle and sheep domestication from farming groups, in Anthony and Brown's view.