700,000-Year-Old Horse Found in Yukon Permafrost Yields Oldest DNA Ever Decoded

The frozen remains of a horse more than half a million years old have reluctantly given up their genetic secrets, providing scientists with the oldest DNA ever sequenced. The horse was discovered in 2003 in the ancient permafrost of Canada’s west-central Yukon Territory, not far from the Alaskan border. And although the animal was dated to between 560,000 and 780,000 years old, an international team of researchers was able to use a new combination of techniques to decipher its genetic code. Among the team’s findings is that the genus Equus — which includes all horses, donkeys, and zebras — dates back more than 4 million years, twice as long ago as scientists had previously believed. To get a better sense of what this new, ancient genome held, Orlando’s team compared it against that of a 43,000-year-old horse, plus modern domestic horse breeds, and finally the Przewalski’s horse, an equid that makes its home on the Asian steppes and holds the title as the last surviving population of wild horses. These full-genome comparisons allowed the scientists to construct “a molecular clock” that can reveal benchmarks in the horse’s evolutionary history, Orlando said. The comparisons also shed light on genetic variations, and therefore population size, over time, Orlando noted, revealing “bursts of expansion” during cooler periods as grasslands grew, and contractions in size during times of warming...more