The discovery has led scientists to believe that DNA reconstruction for animals up to one million years old is possible. The ancient genome, which is from a horse, is more than 700,000 years old. If it is accepted as a specimen, it would extend the reach of paleogenomics, or the study of genomes reconstructed from fossil bones, tenfold.
Before this discovery, the oldest recovered DNA belonged to a Denisovan human that lived 70,000 years ago.
The genome increases the understanding of evolution as well. Scientists compared the genome to modern horses, zebras and donkeys -- all part of genus Equus -- and found that the genus arose about 4 million years ago, twice as long ago as had been thought.
Horses have long been used as a classic illustration of one of Darwin's theories: Ancient equine species, which were five-toed animals the side of dogs, evolved over time into the hooved horses we know today. But as older genomes have been found, scientists have discovered the evolution is not that clean-cut.
The DNA came from a frozen, fossilized bone from an extinct prehistoric horse in the Yukon. Technology developed for genome projects enabled scientists to use the bone, which was covered in microbes -- each with its own set of DNA -- to determine which of the DNA belonged to the horse.
Having such technology available has opened the door to using genomes that were previously thought to be too damaged to use, and to fill in the gaps in existing research. Danish scientists used the horse's genome to predict the horse's gradual change in size over time, and the potential for research on how the climate has affected them and other animals over time.