Horses Evolved 4 Million Years Ago

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Przewalski horses in Khomyntal, Western Mongolia, were imported in 2004 from Le Villaret, France.
Claudia Feh, Association pour le cheval de Przewalski: TAKH, Le Villaret, F 48125 Meyrueis Tak

The ancestor of all living horses, donkeys and zebras lived about four million years ago, suggests a new study, pushing back the confirmed age of the horse’s progenitor by two million years.

The discovery comes from the genetic analysis of a 700,000-year old horse fossil trapped in the Canadian permafrost. That’s hundreds of thousands of years older than any genome ever sequenced before.

Among other insights, the sequence supports the often-debated view that the Przewalski’s horse, native to the Mongolian steppes, is the last living population of truly wild horses in the world.

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And while the new study offers an intriguing look into the history of horses and how they have changed over millenia, the research also opens up the possibility of getting a much longer view into the evolution of all sorts of species, including people.

“This really shows that you can go much further back in time and do genomics than people previously thought,” said Eske Willerslev, an evolutionary geneticist at the University of Copenhagen. “Suddenly, that means that we can potentially go back and do the genome for precursors to Neanderthals. Maybe there’s potential for getting the genome of Homo erectus. From a scientific standpoint, this is really great.”

In 2003, Willerslev and colleagues retrieved a horse fossil from a site in Canada’s Yukon Territory, which contains some of the oldest permafrost on Earth. Based on volcanic ash preserved in the soil, the researchers estimated that the fossil was at least 700,000 years old.

When they scanned the bone for biomolecules, they were surprised to find both collagen and proteins, giving them hope that the bone might also still contain DNA, even though the oldest surviving DNA ever recovered from a fossil to date was only about 130,000 years old.

The team started with classic techniques to amplify DNA and build a genetic library, Willerslev said, but they ran into too much contamination. Most of the DNA they extracted belonged to microbes.