Eleftheria Palkopoulou inspects a woolly mammoth tusk to identify potential sites for DNA sampling on Sept. 3, 2013, in the ancient DNA lab at the Swedish Museum of Natural History in Stockholm, Sweden. (Love Dalen via AP)

Four thousand years after the woolly mammoth vanished from the Earth, scientists have deciphered the genetic blueprint that may offer a key to bringing it back.

By comparing DNA recovered from two long-dead individuals, a team of researchers have sequenced the species’s entire genome — effectively providing a gene-by-gene instruction manual on how to build a mammoth.

Their study of the newly sequenced genome, which was published Thursday in the journal Current Biology, offers all kinds of interesting insights into the animal’s past: when it first appeared, when it suffered from population bottlenecks, how it was affected by climate change.

But for people who work in the small but ambitious field of “mammoth de-extinction,” the genome is just as interesting for the role it might play in the animal’s future.

“This basically gives you the changes that account for a mammoth being a mammoth — the changes that allowed them to have hair, tremendous amounts of fat, large tusks,” co-author Hendrik Poinar, who directs the Ancient DNA Center at McMaster University, told CBS News. “This then gives us this road map, so to speak, of what we would need to change in an Asian elephant chromosome to make them mammoth-like.”

As far as topics in evolutionary biology go, revitalizing the mammoth is a hot one, and there are several projects working to make it happen. The Long Now Foundation, a San Francisco nonprofit dedicated to “long-term thinking,” is working with Harvard researchers to study allele replacement in elephants that might make them more mammoth-like — the kind of effort Poinar was referring to.

George Church, the Harvard geneticist leading the project, announced just last month that his team had successfully spliced mammoth DNA into an Asian elephant genome. The research hasn’t been peer reviewed or published in a scientific journal, Church said, and there’s a lot more research to be done. But by altering modern elephant DNA to resemble that of their ancient relatives, Church and his fellow “revivalists” believe they can make the animals more mammoth-like.

When, and if, he succeeds, the resulting creature won’t be a perfect copy of the shaggy, prehistoric beasts. But it would be capable of repopulating the Siberian tundra, a scheme promoted by Russian scientist Sergey Zimov. At a remote wildlife refuge he calls “Pleistocene Park,” Zimov is trying to reconstitute a 10,000-year-old pasture ecosystem, complete with reindeer, bison, wolves and — of course — mammoths. He believes that returning mammoths, or at least something mammoth-ish, to the tundra would help revive an ancient grassland there. That in turn would prevent the melting of Siberia’s permafrost — an event that could hasten climate change by releasing carbon dioxide into the atmosphere.

“We cannot artificially stop this process. However, pasture ecosystems can,” he wrote in his 2014 “Wild Field” manifesto. “. . . All [that] is needed is to cross mental barriers . . . and return part of the territory which our ancestors took from them.”

It’s an ambitious — and many might say outlandish — proposal, but Zimov and the Long Now “revivalists” are hardly the only people to come up with such a plan. In 2013, mammoth researcher Semyon Grigoriev uncovered an incredibly well-preserved 10,000-year-old carcass, complete with fresh-looking tissue and blood samples.

“This find gives us a really good chance of finding live cells,” Grigoriev told reporters at the time, prompting of flurry of speculation that mammoth cloning was within scientists’ grasp. This March, he and his team extracted DNA from the long-frozen animal, which they named “Buttercup,” hoping to find a viable sample that could be inserted into an elephant embryo. The idea is that the embryo would gestate in a female elephant’s womb and be born a real woolly mammoth clone, not just a mammoth-elephant hybrid.

But scientists said that the likelihood of finding viable DNA is slim.

“In general, ancient DNA is highly fragmented and by no means ‘ready to go’ into the next mammoth embryo,” University of Michigan paleontologist Daniel Fisher wrote to Scientific American in 2013. “. . . Although there is much talk of ‘viability’ of this sort, I think it remains to be demonstrated that any DNA from a mammoth meets this criterion.”


The skeleton of a mammoth stands in the Paul and Irma Milstein Hall of the American Museum of Natural History in New York. (D. Finnin/American Museum of Natural History via AP)

There are ethical as well as logistical questions about reviving the woolly mammoth — even among the scientists who just sequenced the animals’ genome. Paleogeneticist Love Dalén, an associate professor at the Swedish Museum of Natural History and a co-author of the study, said it would be “a lot of fun” to see a living mammoth, but he ultimately hopes that his research isn’t used to this end.

“It seems to me that trying this out might lead to suffering for female elephants and that would not be ethically justifiable,” he told the BBC.

Evolutionary biologist Beth Shapiro, whose book “How to Clone a Mammoth” examines the ethics of de-extinction, added that bringing just one mammoth to life would be cruel to both the mammoth and its elephant mother, without offering much benefit. Mammoths were probably highly social creatures, she told the BBC, and a single living individual would never make it in the wild on its own. Instead the clone would be doomed to a lonely life in captivity.

Others, like Duke University conservation ecology professor Stuart Pimm, say that “de-extinction” is a seductive but dangerous distraction from real conservation efforts.

“Conservation is about finding alternative, sustainable futures for peoples, for forests, and for wetlands. Molecular gimmickry simply does not address these core problems,” Pimm wrote in a 2013 opinion piece for National Geographic. “At worst, it seduces granting agencies and university deans into thinking they are saving the world. It gives unscrupulous developers a veil to hide their rapaciousness, with promises to fix things later. It distracts us from guaranteeing our planet’s biodiversity for future generations.”

Poinar, one of the co-authors on the genome sequence study, has mixed feelings about mammoth resurrection.

“The kid in me wants to see it, of course,” he told CBS. But the ethical and logistical challenges are overwhelming, he said, and not necessarily worthwhile just to produce a single specimen for zoo-goers to gawk at.

Even if the genome sequence is never used for a de-extinction effort, the study still contains much of interest to mammoth lovers. By comparing DNA from a 45,000-year-old individual with one that was just a tenth of that age, the study paints the most complete picture to date of the arc of mammoth history: when they first appeared, how their population fluctuated under environmental pressures and hints at why the species eventually died out.

One of the biggest mysteries the genome sequencers uncovered was an unexplained decline in the population around 300,000 years ago.

“It seems like there was an ancient bottleneck,” Dalen told the BBC.

Modern humans were nowhere in the region, so the species couldn’t have been over-hunted. Instead, it’s possible that climate change caused the mammoths to die out in large numbers around that time. But the decline doesn’t correspond with a major glaciation event, Poinar told CBS, so it’s unclear what was happening to cause such a dramatic drop.

Eventually the mammoth population rebounded, and it persisted until about 4,000 years ago.

The second DNA sample studied by the genome researchers came from one of the last surviving woolly mammoths, which by then were confined to Wrangel Island off Siberia’s northern coast. These animals had much less genetic diversity than their ancestors — likely a result of inbreeding — and that may have led to their extinction, Dalen said.

Answers to those lingering questions, and to questions biologists haven’t even thought of yet, will probably be found in the newly sequenced genome, he added.

“Genomes are rich sources of information, and we have only tapped the surface.”