Danish geneticists have mapped the DNA of a 700,000-year-old horse bone, yielding the world's oldest full genome. National Geographic reports that Ludovic Orlando, an evolutionary geneticist with the Natural History Museum of Denmark, and his team identified key patterns in Equus evolution — the group of animals that include horses, donkeys, and zebras — tracing the genus' ancestry back two million years earlier than it was originally believed to have emerged.

The 5-inch fossil bone fragment was found in the permafrost of a Yukon gold mine. The previous oldest animal fossil to be genetically mapped belonged to a Paleolithic relative of Neanderthals known as Denisovans dating back about 75,000 years. Although the horse bone had degraded over time, geneticists were able to isolate different proteins and used new techniques to extract DNA molecules. Orlando noted that for every 200 molecules his team sequenced only one actually belonged to the horse — the rest were from bacteria that colonized it after the horse had died.

The analysis also presented evidence that the endangered Przewalski's horse — originating in Mongolia and China — is the last surviving wild horse. Orlando believes the study could help map the genomes of organisms that are more than a million years old, helping trace the evolution of animals and mammals that existed in even colder climates.