DNA From A 700,000-Year-Old Horse Fossil Reveals Modern Horses Evolved 4 Million Years Ago

The genome found in a fossilized bone of a prehistoric horse that roamed Canada’s Yukon Territory some 700,000 years ago, has led scientists to determine that modern horses evolved millions of years earlier than was previously estimated.

Scientists at the University of Copenhagen extracted the genome sequence from the bone of a horse's foot and matched it against other DNA sequences such as that of a 43,000-year-old horse, five modern domestic horse breeds, a wild Przewalski’s horse, and a donkey.

After analyzing the results, the researchers estimated that the ancient ancestors of modern horses, as well as donkeys and zebras, dated back to about 4 million years -- twice as old as what scientists had earlier determined.

According to the scientists, the DNA discovered from the horse fossil is nearly 10 times older than any other animal genome mapped so far. The previous oldest DNA sequenced belonged to a polar bear that existed between 110,000 and 130,000 years ago, said the study, published in the Wednesday issue of the journal Nature.

“We have beaten the time barrier,” Ludovic Orlando, of the University of Copenhagen, said in a statement. “All of a sudden, you have access to many more extinct species than you could have ever dreamed of sequencing before.”

Scientists said that they were successful in sequencing such an old DNA mainly because of two factors: the cold ground temperatures that prevented faster DNA decay and improved techniques to extract genome while preserving its quality for sequencing.

Scientists believe that they will be able to apply these perfected techniques to other genus, such as ancient human species, which existed more than one million years ago.

As part of their discovery, the scientists also examined the genome of the endangered Przewalski's horse found in Mongolia and China, and confirmed that it is truly the last remaining wild horse when compared genetically with domesticated horses.

Przewalski’s horse, named after a Russian colonel who discovered the species in 1881 while on an expedition in Mongolia, was brought back from near-extinction in the region by captive-breeding programs in the 1990s.

According to Orlando and his colleague Eske Willerslev, the ancient horse could theoretically be brought back to life by implanting a modern horse egg with the ancient DNA. However, they don’t have any plans to do so as they are now looking to further improve on their DNA-extraction techniques.

Scientists believe that the study will have a significant impact on evolutionary biology in days to come as “ancient genomics will change a lot of the ways we look at evolution to date.”

“This kind of study is giving us novel views that show us the nuts and bolts of how evolution is working,” Alan Cooper, director of the University of Adelaide's Australian Center for Ancient DNA, said.