The wide origins of domesticated horses offers insight on how our love affair with the animal has transformed humankind.
Horses may have been domesticated independently in at least 18 different places.
The ancestor of all modern horses lived about 140,000 years ago.
The domestication of horses transformed human history.
The domestication of wild horses had a profound effect on human history -- offering nutrition, transportation and a leg up in warfare, among other advantages. But there are still many unanswered questions about when and where our species began its long love affair with horses.
A new genetic study offers some clues. Through the first complete analysis of equestrian mitochondrial DNA -- a kind of genetic material that is passed directly from mother to offspring -- an international group of scientists was able to trace all modern horses to an ancestor that lived about 140,000 years ago.
After horse domestication began about 10,000 years ago, the study also discovered, horses diverged into at least 18 distinct genetic lines. Those findings suggest that, unlike cows and other animals, horses may have been tamed independently in many different places around Europe and Asia.
The new research could help scientists decode the genetic secrets of modern horse breeds and top racehorses.
"Horse domestication had major cultural, socioeconomic, and even genetic implications for the numerous prehistoric and historic human populations that at different times adopted horse breeding," said Alessandro Achilli, a geneticist at the University of Perugia in Italy. "Thus, our results will have a major impact in many areas of biological science, ranging from the field of animal and conservation genetics to zoology, veterinary science, paleontology, human genetics and anthropology."
Cows, sheep, and goats had simple beginnings as livestock, with evidence suggesting that a small number of animals of each species were domesticated in just a few places between about 8,000 and 10,000 years ago. Today, genetic diversity among these creatures remains low.
Horse DNA tells a different story, according to a new paper published today in the Proceedings of the National Academy of Sciences. After analyzing mitochondrial DNA from a wide range of horse breeds across Asia, Europe, the Middle East and the Americas, and then using the known mutation rate of this kind of DNA as a sort of clock, Achilli and colleagues were able to connect all modern horses to a common ancestor that lived between 130,000 and 160,000 years ago. By comparison, modern humans first evolved about 200,000 years ago.
Previous research focused only on limited regions of mitochondrial DNA in horses. But by looking at the entire mitochondrial genome, the new study was able to categorize horses into at least 18 different groups that evolved independently.
One possible explanation for those findings is that many different groups of people independently discovered the dramatic benefits of taming wild horses thousands of years ago.
"The very fact that many wild mares have been independently domesticated in different places testifies to how significant horses have been to humankind," Achilli said. "It means that the ability of taming these animals was badly needed by different groups of people in different regions of Eurasia, from the Asian steppes to Western Europe, since they could generate the food surplus necessary to support the growth of human populations and the capability to expand and adapt into new environments or facilitate transportation."
Results also showed that horses managed to survive in modern-day Spain and Portugal during a glacial period more than 13,000 years ago, when horses, humans and other mammals disappeared north of the Pyrenees. The area has shown to be an important refuge during that time for people, who later went on to repopulate Europe when conditions improved. The new study suggests that horses may have followed a similar pattern.
The new findings offer another potential explanation for the origins of domesticated horses, said Alan Outram, an archaeologist at the University of Exeter in the United Kingdom. Horses may have been originally domesticated in one area, he said, such as the central Asian steppe. Then, people could have transported tamed stallions to other cultures in other places, where they were bred with local, wild mares. That scenario would also create multiple distinct female genetic lines.
Either way, the new study adds important context to the puzzle of how horses infused themselves into people's lives.
"One thing that is clear is that the domestic horse revolutionized human life, making us much more mobile, changing our trade patterns and modes of warfare," Outram said. "Such changes affected the whole way in which societies were organized and interacted with each other."