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Scientists Decode Oldest Genome Ever, Prove Evolution of Horses Much Slower Than Believed

Jun 27, 2013 10:48 AM EDT
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Horses originated approximately 2 million years before originally believed, according to scientists who sequenced the genome of a 700,000-year-old relative of the modern-day horse preserved in the permafrost of Canada's Yukon Territory.

Not only did the results of the sequencing shed light on the evolution of horses, but as the oldest genome ever sequenced, the researchers have pushed the boundaries of the science to a new realm.

"We've beaten the time barrier," evolutionary biologist Ludovic Orlando of the University of Copenhagen and one of the overseers of the study told the journal Nature. "All of a sudden, you have access to many more extinct species than you could have ever dreamed of sequencing before."

Previous to this case, the oldest DNA sequence belonged to a polar bear that lived some 110,000 to 130,00 years ago.

One reason for the group's success, Nature reported, was due to the techniques they employed for extracting and preparing the DNA to preserve its quality.

Targeting tissue within the fossil where a high degree of DNA is found, they combined DNA sequencing methods to get maximum coverage. This included routine next-generation sequencing with single-molecule sequencing in which a machine reads the DNA directly without amplifying it.

The team then compared the ancient horse DNA to that of five domestic breeds, as well as a donkey and the Przewalski horse, according to New Scientist. As they did this, they found that the last common Equus ancestor lived between 4 and 4.5 million years ago, placing it before the last Ice Age and rendering it twice as old as previously believed.

What this means, Orlando told LiveScience, is that horses and their ancestors are evolving more slowly than expected.

"The whole horse history is driven by changes in climate," New Scientist reported Eske Willerslev of the University of Copenhagen as saying, explaining that they thrived when the ice sheets advanced and suffered when the temperatures rose.

Furthermore, the researchers were able to prove once and for all through their research that the Przewalski horse is indeed the last remaining wild horse.

Going forward, the team is sequencing a more recent species, which lived shortly before horses were domesticated in order to figure out how the process changed its genetic make up.

For other researchers, however, the major challenge from this point on is applying the techniques used to decipher the ancient colt's DNA to other species, including the Homo erectus.

"The real challenge right now in the field is combining these next-generation sequencing technologies with the possibility of analyzing non-permafrost samples," Carles Lalueza-Fox, a paleogeneticist at the Institute of Evolutionary Biology in Barcleona, Spain who was not involved in the study told Nature.

For those who master this challenge, the reward will be a more detailed look at the evolution of humanity than has ever existed.

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