Ancient horse DNA, a record-breaking 700,000 years old, may open the door to mapping the genes of many extinct creatures, including humanity's ancestors.
Gene experts said Wednesday they've been able to unravel the genetic blueprint of a prehistoric horse that lived in Canada some 700,000 years ago, the oldest DNA mapping effort ever attempted.
A dramatic extension of the limits of ancient DNA recovery, the advance re-creates a gene map, or genome, which is roughly 10 times older than the previous record-holder. The feat suggests that ancient DNA may be recoverable from frozen remains almost a million years old, raising the possibility of someday recovering even more ancient gene maps of humanity's primitive ancestors.
"Obviously (this) opens great perspective as to the level of details we could reconstruct of our own origins," says study lead author Ludovic Orlando of Denmark's University of Copenhagen. "And actually the evolutionary history of almost every species living in the world today."
A research team in 2003 discovered the horse bones encased in the oldest known permafrost, at the Thistle Creek site in Canada's Yukon. The bones initially yielded promising signs of blood and other tissues, which encouraged the team to try DNA mapping. For comparison, the team also genetically mapped a DNA sample from a 43,000-year-old-horse, similarly frozen, as well as five modern horses, a donkey and a modern-day Przewalski's horse.
Horses as a distinct species appear to have split from donkeys 4 million years ago. The results also confirm the Przewalski's horse, an endangered breed now found in zoos and sanctuaries in Mongolia, as the last wild survivor of all horses, splitting from domestic horses about 50,000 years ago. The genes indicate that horse populations went through a series of booms and busts tied to various Ice Ages that expanded grasslands over the last 2 million years. It also points to a genetic "bottleneck" that horses went through on their way to domestication, finding genes related to blood cells, fertility, color and muscle unique to modern horses and absent in their ancient counterparts.
The team assembled the 700,000-year-old gene map using "short" DNA sequences preserved in a leg bone, a capability that technology has only recently afforded to researchers. Had the DNA not been frozen for the entirety of the time since the horse died, team members expressed doubt that even that would have been possible. In theory, the ancient horse DNA could be reconstructed and used to clone a version of the now-extinct species, a kind of "de-extinction" now widely debated by genetics researchers.
"Somewhere in between a pointer to the future and a one-off," says evolutionary molecular biologist Tara Fulton of the University of California, Santa Cruz, who was not on the study team. "It is also a matter of finding these specimens in the permafrost or sometimes in consistently cool northern caves and even in ideal preservational conditions. The DNA is unlikely to survive too much past a million years."
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."