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Domesticated horses are about three centuries younger than the Pyramids of Giza, researchers have found, as they uncover the origin of all modern domestic horses.
Scientists found that modern horses come from central Asia, and rapidly replaced all of their relatives around 4000 years ago.
The origin of domestic horses has been unpicked by scientists, revealing how the animals we know today came into being.
Scientists found that the ancestors of modern horses were domesticated in the northern Caucasus region in what is now southern Russia. They were bred for their stress tolerance and back strength, allowing humans to use them for transport, farming and warfare.
Around 4000 years ago, these horses rapidly spread and replaced all other groups across Europe and Asia, becoming an integral part of human culture across the continents.
Dr Pablo Librado, the lead author of the study, says, 'Horses living in Anatolia, Europe, Central Asia and Siberia used to be genetically quite distinct. Then, around 2200-2000BCE, genetic data points to an explosive demography at the time, with no equivalent in the last 100,000 years.
'This is when we took control over the reproduction of the animal and produced them in astronomic numbers.'
The international team of scientists, led by French researchers, published their findings in Nature.
The earliest recognised ancestor of horses is Eohippus angustidens, known as the dawn horse. It was a small North American animal around the size of a fox which lived in forests and ate fruits, shoots and leaves around 55 million years ago.
Over the following tens of millions of years, horse ancestors such as Mesohippus grew in size. As grasslands expanded around 20 million years ago, species like Parahippus became more adapted to eating grass.
Its descendants also became better at running, with the bones of the leg fusing together and the number of toes reducing to allow it to evade predators on the open plains. Some horses also spread across a land bridge into Asia and Europe, a process that continued periodically over millions of years.
The genus Equus, which includes modern horses, zebras and donkeys, first appeared around five million years ago and subsequently spread across the world. While sharing many of the major adaptations of modern horses, such as 'spring feet' which cushion their legs while running, these horses were still quite different from those that are known today.
With horses going extinct in North America around 10,000 years ago, the animals were confined to just Asia and Europe. While their history is well-known until this point, the picture soon becomes much less clear.
For instance, the oldest known domesticated horses are from Botai, an ancient civilisation which lived in what is now Kazakhstan. Archaeological evidence suggests the animals were being ridden, as well as milked for food, but they are not closely related to modern domesticated horses. But to confuse things further, there is also evidence which suggests that horses were domesticated multiple times right across their range.
In 2016 a project known as Pegasus was launched to try and solve the issue once and for all. Now, researchers are confident that they have finally pieced together where the domesticated horse comes from.
Researchers gathered together horse remains from all the areas of Europe and Asia where horses are believed to have been domesticated, including what is now modern-day Spain, Turkey and the steppes of Asia.
They found that there were around four different lineages of horse before domestication, centred in Siberia, France, Spain and the northern Caucasus. But by around 4200 years ago, the Caucasus horses began to spread out across both continents.
This group of horses had significant modifications in the gene associated with chronic back pain in humans, as well as another involved in anxiety and fear in mice. This suggests that humans in the northern Caucasus were selecting for horses that were more docile and stress resistant, as well as being able to carry heavier loads.
This parallels archaeological finds in the area, which suggest that the first recognisable chariots were developed shortly after this period. Stronger horses from the Caucasus would have been in demand in war, which may have helped them spread more quickly and lead to technological developments.
Another factor that may have helped these horses spread is that a population fall in Europe at the time, attributed to a famine, may have allowed people from Caucasus to expand westwards.
By around the start of the Iron Age in 1000BCE, modern horses had replaced all others across Europe and Asia. Their descendants would later be reintroduced to the Americas in the sixteenth century AD, bringing horses back to their ancestral homelands.
Scientists hope that uncovering the origins of the modern horse not only allows us to understand more about the animals themselves, but also their impact on early humans and their cultures.