Horses and Man: Digging Up the Truth about Domestication

There are a number of theories regarding the timing and location of the first domesticated horses. The clearest archeological evidence of domestication is from chariot horse burials circa 2000 BC; however, there is evidence that horses were domesticated in the Eurasian steppes much earlier.

Assyrian war chariot.

Discoveries in Kazakhstan may suggest that the earliest use of horses ‒ beyond those being hunted for meat ‒ was occurring around 3500 BC. But even this may not be the final word.

Defining Domestication

Of course, determining the start date of domestication depends somewhat on the definition of ‘domestication’ itself. It may be as basic as human control over breeding, which can be seen in skeletal remains showing changes in size and variability of ancient horse populations. Some zoologists look at broader human-related evidence including skeletal and dental evidence of working activity (such as bit wear on the teeth) and weapons, art and other artifacts. There are certainly theories that horses were kept as meat animals, rather than relying solely on hunting, before being used for work or warfare.

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The recent attempts to date equine domestication by genetic analysis of physical remains rests on the assumption that there was a separation of genotypes between domestic and wild populations. While this is believed to have occurred, these dates are unlikely to be specific as it was likely there was a flow of genetic material between the wild and human-kept populations due to escapes from captivity or the capture of breeding stock from wild herds. In fact, mitochondrial DNA (containing genes inherited solely from the mother) suggests horses were domesticated many times, in different places. It is likely that wild mares were used to re-stock domestic herds, perhaps because they did not breed easily in captivity, or because domestic mares were too useful for other purposes (such as milk).

Cave painting in Lorstan, Iran, 8th millennium BC.

Mixed Messages from Botai

Considerable data uncovered in the late 2000s seemed to point towards a compelling case for the first domestication occurring on a site called Botai in northern Kazakhstan, dating back about 5,500 years ago. Nearly all the animal bones found were from horses. The animals were butchered and eaten and their bones were used to make tools. In a startling discovery in 2009, a new technique that analyzes fat residues suggested that the ceramic vessels at Botai had contained horse milk. This biomolecular evidence suggested that they raised and cared for the horses as livestock. It was assumed by many that continent-wide dispersal of Indo-European peoples began here, assisted by the horse.

Most recently, however, new information has triggered serious doubts about the Botai/Indo-European model of domestication. In a 2018 study, a French research team revealed that the horses of Botai were in fact not the domestic horse (Equus caballus) at all, but instead Equus przewalskii – the wild Przewalski’s horse, with no documented evidence of management by human societies.

Another project using ancient DNA analysis of human remains from Botai showed no genetic links between the area’s ancient residents and Indo-European groups, undermining the idea that horse domestication at Botai stimulated a continental migration on horseback. Some, including the equine DNA researchers who published the new discoveries, now suggest that Botai represents a separate, failed domestication event of the Przewalski’s horse.

The ‘domestic horses’ of Botai were in fact the wild Przewalski’s horse. (Olaf Janssen/Pixabay)

Back to Square One?

So we are back to the most reliable evidence being the chariot horse burials of Russia and Central Asia, placing Equus Caballus as arising about 2000 BC. Yet researchers continue to study ancient peoples and use DNA to track evidence of domestication. DNA and biomolecular data must be matched with archeological findings, such as skeletal clues, to determine when – and how – horses were cared for and used. Species identifications must be made using DNA rather than assumed, as at Botai, that domestication was a linear, one-time event.

In the future, the story of how humans and horses first connected will be an interesting one to follow as new evidence comes to light.