In two weeks’ time, Australia will stop for a few minutes to watch the winner of the Melbourne Cup gallop into history.
- The origin of where and when modern horses were first domesticated is a longstanding mystery
- An international team of scientists has analysed DNA and dated bones from all the groups of horses known to have lived in Eurasia, where horses evolved
- The findings reveal all horses today are linked to a group that lived in the Western Steppes of Russia 4,200 years ago
But the story of the horses in this race begins long before the powerful steeds spring out of the barriers.
The genes of these sleek thoroughbreds can be traced back 4,200 years to the grasslands between the Volga and Don Rivers in Russia.
This is where and when the ancestors of all modern horses, from flighty thoroughbreds to stocky workhorses, were first domesticated, according to a new study that claims to finally settle a longstanding mystery.
Within just a few centuries, these horses had spread right across Asia and Europe, said the study’s lead author Ludovic Orlando, director of the Centre for Anthrobiology and Genomics of Toulouse.
“This is one of those historical turning points that we identify,” Professor Orlando said.
The study, which was published in the journal Nature, suggests genes that made these animals more docile and robust gave them the leg-up in the evolutionary race.
Paired with later innovations such as spoked-wheel chariots, they helped shape human civilisation.
The ‘overnight’ rise of domesticated horses
Professor Orlando has spent the past decade trying to pinpoint just where and when horses were first domesticated.
It was once thought that today’s horses rose from a group that was domesticated for their meat and milk by Botai herders further to the east in Kazakhstan, around 5,500 years ago.
But a previous study by Professor Orlando and colleagues established these horses, even though they were likely to be domesticated, were not related to modern horses.
Instead, they were genetically similar to Przewalski’s horse, a different species or subspecies of horse that has been reintroduced into Mongolia, where it runs wild.
“The Botai horses did not give rise to the present-day genetic variation present in horses today,” Professor Orlando said.
“It was clear we needed something else to start looking at this old archaeological debate.”
So the 160-strong team decided to map the genomes and date fossils from all of the different groups of horses known to have existed in Eurasia between 50,000 BC and 200 BC.
They gathered remains from 273 ancient horses from locations including Siberia, Iberia, Anatolia and the steppes of Western Eurasia and Central Asia, and compared these with the modern horse genome.
They identified four separate groups of horses.
The earliest ancestors of the modern horse came from Siberia, but the closest genetic match to horses we know today came from the lower Don-Volga region, north of the Black and Caspian Seas.
“The region we nail down is pretty narrow, about 500 kilometres [in area],” Professor Orlando said.
Within a few centuries, the genetic imprint had started to appear in Anatolia and Kazakhstan, and by 3,500 years ago they were everywhere.
“It goes really fast, it almost takes place overnight.”
But this is more than a story about the movement of horse genes.
Complex history of humans and their horses
Around 5,000 years ago, there was a mass migration of nomadic herders known as the Yamnaya from the Western Steppes west into Europe.
The archaeological and DNA record shows these big-boned people brought with them new languages and contributed up to 30 per cent of the genetic heritage of people in Europe today, said study co-author Morten Allentoft of Curtin University.
“One of the main speculations was that horse domestication facilitated the movements of these humans,” Professor Allentoft said.
Although the Yamnaya took horses with them, possibly as meat and milk, genetic mapping in the study reveals they were not the ancestors of domesticated horses today.
“This is not the lineage we know today because it wasn’t optimised for carrying people,” Professor Allentoft said.
Instead, the spread of the horse as we know it appears to be aligned with the later movement east into Asia by another civilisation known as the Sintashta.
“This is a warrior culture that has a very advanced weapon industry,” Professor Allentoft said.
The genetic evidence shows the Sintashta bred huge numbers of horses that were suitable for riding over long distances and going into battle.
Sweeps of the genomes reveal changes in two regions that are still present in modern-day horses.
One is the mutation of a gene called GSDMC, which is associated with narrowing of nerve canals in the spinal vertebrae, back pain, and difficulty walking in humans.
The other is the mutation of a gene called ZFPMI, which is associated with anxiety in other animals such as mice.
A few centuries after the Sintashta tamed their horses, they developed a new weapon: the spoked-wheel chariot.
These vehicles were much lighter and faster than solid wheel carts used by other civilisations such as the Yamnaya.
With superior horses and chariots, the Sintashta conquered Central Asia, resulting in an almost complete turnover of human and horse genetics in this region.
Valued for their chestnut-coloured coats, endurance and temperament, the lineage of horses first bred on the Western Steppes also became a commodity and status symbol in Europe and in the Levant.
“They reached all parts of Europe, even the northernmost parts, then replaced the local breeds because they were much better adapted,” Professor Allentoft said.
By the late Bronze Age around 1500 BC to 1000 BC, the horses had replaced all the local populations, the study found.
A true tale of evolution
Claire Wade, an animal geneticist at the University of Sydney, said the series of dates revealed by the genetics presented in the paper was very convincing.
“The overwhelming evidence in this paper suggested that domesticated horses came from the Western Steppes area,” she said.
Professor Wade, who led a team that sequenced the modern horse genome in 2009, said piecing the history of evolution together using genetics provided a clearer picture than using archaeological records alone.
“A lot of presumed theory has been based on archaeological findings but the thing with genetics is that [genes] kind of don’t lie,” she said.
“99.9 per cent of the time [DNA] is highly accurate and when you work in genomics, you really see how evolution works every day.”
Through a process known as genetic drift, new mutations come along, and processes such as selective breeding can make mutations disappear.
“Now they know who the ancestor was they’ve been able to step back in time in that ancestral lineage and compare [the four groups] and identify the genes that have changed most along that gradient.”
The question is whether or not the two genes identified were really instrumental in the taming of the horse, and if they are now fixed in modern horses.
“In my experience, things rarely get absolutely or utterly fixed,” Professor Wade said.
“There are still those wild genes or those old genes that float around in the population at low frequencies.
“So it might be interesting to see if those genes drift away in brumbies, to see if the reverse can happen.”