DNA from 2,000-year-old stallions is helping rewrite the story of horse domestication.
Ancient domesticated horses had much more genetic diversity than their present-day descendants do, researchers report in the April 28 Science. In particular, these ancient horses had many more varieties of Y chromosomes and fewer harmful mutations than horses do now.
Previous studies based on the genetics of modern horses concluded that domestication must have squeezed out much of the diversity seen in wild horses before the Ice Age. But the new findings suggest that the lack of diversity is a more recent development.
“Today, Y chromosomes of all horses are pretty much the same,” says evolutionary geneticist Ludovic Orlando of the Natural History Museum of Denmark in Copenhagen. As a result, scientists thought that ancient people started domesticating horses by breeding only a few stallions to many different mares.
“But when we look in the past — wow! — this is a whole new planet,” Orlando says.
Horses are thought to have been domesticated by about 5,500 years ago. Orlando’s group examined DNA from the bones of 15 Iron Age stallions from the ancient Scythian civilization: Two stallions were from a 2,700-year-old grave site in Russia and 13 were sacrificed in a burial ritual about 2,300 years ago in Kazakhstan. The team also looked at a 4,100-year-old Bronze Age mare from the Sintashta culture in Russia. Nearly all of the stallions had a different type of Y chromosome, Orlando says.
That finding challenges the idea that only a few stallions participated in the early stages of domestication. Loss of Y chromosome diversity among horses must have happened within the last 2,300 years, Orlando says, and maybe as recently as 200 to 300 years ago, when people started creating specific horse breeds. Read more at ScienceNews.org »
People like this woman in Kazakhstan (seen milking a horse) still drink horse milk, a practice that started more than 5,000 years ago. Genetic data from ancient Scythian horses indicates that more than 2,000 years of domestication caused changes in horse genes related to mammary gland development and milk production.
Present-day horse breeds have less genetic diversity than domesticated horses did around 2,000 years ago. Free image.