Decoding the mammoths' DNA profile also takes the notion of bringing the massive beasts back to life — or de-extincting them — one step closer to reality, said Hendrik Poinar, director of the Ancient DNA Centre at McMaster University and the senior Canadian scientist on the international research project.
"This discovery means that recreating extinct species is a much more real possibility, one we could in theory realize within decades," said Poinar.
"With a complete genome and this kind of data, we can now begin to understand what made a mammoth a mammoth ... and some of the underlying causes of their extinction, which is an exceptionally difficult and complex puzzle to solve."
The research team — including scientists from Harvard, the Swedish Museum of Natural History and Stockholm University — analyzed the genomes of two male mammoths that had been preserved in permafrost.
One lived in northeastern Siberia an estimated 45,000 years ago. The other was found on Russia's Wrangel Island, in the Arctic Ocean, and is believed to be from one of the last surviving mammoth populations, which lived about 4,300 years ago.
"So Egyptians are building pyramids and you have woolly mammoths up on these small islands in northern Siberia," Poinar said.
The work was painstaking: scientists used sophisticated technology to retrieve highly fragmented bits of DNA from molars of the ancient specimens, which were then used to sequence the genomes — the genetic blueprint, or instruction manual, for making a particular species.
"They're interesting," Poinar said of the two recovered animals, "because they represent sort of two time points of extinction for the mammoth."
Through their analysis, the researchers determined mammoth populations had suffered a significant setback roughly 250,000 to 300,000 years ago — why isn't clear — but the species bounced back.
The specimen that lived 45,000 years ago was among a widespread population of the massive tusked creatures, whose range stretched across northern Siberia, Alaska, the Yukon and Northwest Territories, "all the way across to Nova Scotia," said Poinar.
"Basically all those of the large continental mammoths were extinct about 10,800 years ago," he said, noting that the end of the species coincided with major climate change and persistent hunting by humans.
However, genetic analysis of the Wrangel Island mammoth suggests the hairy behemoths were steadily shrinking in size over time, an evolutionary response to dwindling resources in their water-locked habitat.
Being cut off from the mainland also had another effect that contributed to the woolly mammoth's final doom, about 4,000 years ago.
"We found that the genome from one of the world's last mammoths displayed low genetic variation and a signature consistent with inbreeding, likely due to the small number of mammoths that managed to survive on Wrangel Island during the last 5,000 years of the species' existence," said co-author Love Dalen of the Swedish Museum of Natural History.
Inbreeding leads to an increase in abnormalities, a greater susceptibility to disease, and a diminished ability to adapt to a changing environment, explained Poinar.
"So we understand why these guys didn't stick around."
But when it comes to the "Jurassic Park" idea of de-extincting animals using ancient DNA, he said there are two questions: "Can we?" and "Should we?"
Many technological hurdles would have to be overcome before scientists could bring forth a mammoth-like animal, which would likely be gestated using a surrogate elephant mother, with the hope she could carry the relatively massive offspring to term.
As to whether it should be done, there are pros and cons. Discussions about the ethics of reviving a long-lost species will need to continue as the science moves forward, said Poinar, who comes down on neither side of the argument.
"I think it will happen in the near future," he said. "Whether that's 20 or 50 years, I can't really (predict)."
The research was published online Thursday in the journal Current Biology.
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