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The Domestication of the Horse

1For most of human history, the horse was prey. Bone deposits at sites across the Eurasian steppe show that horses were hunted for meat for tens of thousands of years before anyone thought to ride one. The change, when it came, was among the most consequential in human history: a domesticated horse extended the distance a person could travel in a day roughly fivefold, and with it the reach of trade, of language and of war.

2Establishing when that change occurred has proved unexpectedly difficult. The bones of an early domestic horse look very like those of a wild one, because the physical changes that domestication brings — smaller size, more variable colouring — take many generations to appear and are easily confused with ordinary variation between regions. Archaeologists have therefore had to look for indirect evidence, and three lines of it have proved useful.

3The first is the age and sex of the animals found at a site. Hunters killing wild herds take whatever they encounter, producing a mixture of ages and both sexes. Herders managing a domestic population behave differently: they keep the females for breeding and slaughter surplus young males. A site whose horse bones are overwhelmingly from young males therefore suggests management rather than hunting. Several settlements of the Botai culture, in what is now northern Kazakhstan, show exactly this pattern in deposits dated to around 3500 BCE.

4The second line of evidence is damage to the teeth. A horse that is ridden or driven with a bit carries a hard object in its mouth, and over time the animal pushes at it with the second premolar, producing a characteristic wear facet that does not occur naturally. In the 1990s researchers examined Botai horse teeth and reported such wear, arguing that these animals had been bridled. The finding was influential, though some specialists have since questioned whether similar marks can be produced by other causes, and the debate has not been entirely settled.

5The third line is chemical. Pottery absorbs fats from whatever is cooked or stored in it, and those fats survive for thousands of years. Analysis of Botai pottery found residues whose composition matches mare's milk. Since it is extremely difficult to milk a wild mare, the residue is strong evidence that the animals were under human control. Together with the tooth wear and the pattern of ages, it made the Botai the accepted candidates for the first horse keepers.

6Then genetics complicated the picture. In 2018 a study of ancient horse DNA produced a surprise: the Botai horses were not the ancestors of modern domestic horses at all. They were most closely related to Przewalski's horse, the stocky wild horse of the Mongolian steppe, which had itself been assumed to be the last truly wild horse. The relationship, it now appeared, ran the other way — Przewalski's horse is probably descended from animals that the Botai had domesticated and that later escaped.

7If the Botai horses were a dead end, where did modern horses come from? A large study published in 2021 traced the ancestry of nearly every domestic horse alive today to a single population in the lower Volga-Don region of what is now southern Russia, around 2200 BCE — more than a thousand years after the Botai. From roughly 2000 BCE this lineage spread with remarkable speed across Eurasia, replacing local horse populations almost everywhere it went.

8What made it spread so successfully is still debated. The genetic work identified changes in two genes, one associated with a stronger back and one with a calmer disposition — precisely the qualities that make an animal easier to ride for long distances. Whether those changes were the cause of the expansion or merely accompanied it is not something DNA alone can settle.

9The revised story is less tidy than the old one, and that is its virtue. Domestication was not a single event but a process attempted more than once, in more than one place, with at least one attempt leaving no descendants at all. It is a useful reminder that in archaeology the first example found is rarely the first that occurred.

The Domestication of the Horse

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