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The Oldest DNA: Mapped from a 700,000-year-old Horse

The humble horse has provided the oldest full genome sequence of any species; from a specimen over half-a-million years old, found frozen in the permafrost of the Canadian Arctic.  The finding, published in Nature today, pushes back the known origins of the equine lineage by about 2 million years, and yields a variety of evolutionary insights and possibilities.

The Przewalski’s horse, recently brought back from the brink of extinction in Mongolia, is truly the last remaining wild horse, suggests the new study.

The sequence was extracted from a foot bone of a horse that lived between 780,000 and 560,000 years ago.  By sequencing the animal’s genome, along with those of a 43,000-year-old horse, five modern domestic horse breeds, a wild Przewalski’s horse and a donkey, researchers were able to trace the evolutionary history of the horse family in unprecedented detail.  They estimate that the ancient ancestor of the modern Equus genus, which includes horses, donkeys and zebras, branched off from other animal lineages about 4 million years ago, twice as long ago as scientists had previously thought.

Two pieces of a 700,000-year-old horse metapodial bone are shown, just before being extracted for ancient DNA.

“We have beaten the time barrier,” says evolutionary biologist Ludovic Orlando of the University of Copenhagen.  Noting that the oldest DNA sequenced before this came from a polar bear between 110,000 and 130,000 years old, Orlando says: “All of a sudden, you have access to many more extinct species than you could have ever dreamed of sequencing before.”

The team was able to sequence such old DNA partly because of the freezing ground temperatures in the area where the bone was found, which would have slowed the rate of DNA decay.


Other researchers go further. Given that ancient human species at times lived in cold climes, the ancient horse gene map raises the possibility of recovering even more ancient human DNA, suggests biologist Craig Millar of New Zealand’s University of Auckland and David Lambert of Australia’s Griffith University, in a commentary on the discovery. The results, they write, raise “the tantalizing proposition that complete genomes several millions of years old may be recoverable.”


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