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Cloned cow embryos are moved with a pipette.

A pipette that's being used to manipulate cloned cow embryos.

  Photograph by Mauro Fermariello, Science Source  

Brian Switek

for National Geographic News

Published March 10, 2013

Will we ever see a woolly mammoth again? What about the striped Tasmanian tiger, once-prolific passenger pigeon, or the imposing wild cattle called aurochs?

Our species has played a role in the extinction of these and many other species. But now some scientists are proposing a radical turn of the tables: Bringing lost species back from the dead.

Video: Recipe for Resurrection

Three main methods for "de-extinction" have been proposed. Cloning gets the most attention, thanks in part to the science fiction of Jurassic Park. We probably won't ever see a Tyrannosaurus—despite the discovery of degraded soft-tissue remnants in fossilized dinosaur bone, no one has ever found non-avian dinosaur DNA—but cloning is plausible for less ancient creatures whose genomes can be reconstructed.

And while mammoths tend to hog the spotlight when such proposals are discussed, researchers are also considering resurrecting other species that might not be as famous, but are equally charismatic. (See "Pictures: Extinct Species That Could Be Brought Back.")

 

mammoth picture

 

The thylacine, also known as the Tasmanian tiger, is one such lost species. These striped carnivores appear superficially doglike but are actually marsupials that once roamed Australia, Tasmania, and New Guinea. A combination of causes—most prominently hunting and trapping by humans—totally wiped them out by 1936.

But as paleontologist Michael Archer has realized, the relatively recent extinction of thylacines means that museum specimens can still yield viable genetic material. When he was the director of the Australian Museum in the early 2000s, he and his colleagues extracted DNA samples from the teeth, skins, and dried tissues of thylacines in the museum's collection.

Obtaining those genetic sequences was just the first step, though. The DNA is in fragments, and the next major task will be assembling all those snippets into the whole genome of the thylacine.

Although Archer discontinued the project when he left the museum for a position at the University of New South Wales, he's optimistic that researchers can someday pick up where he and his team left off: "As technology improves, and sequencers get better and better, it would be a brave person to declare that the whole nuclear genome won't ever be able to be reconstituted."

If the thylacine genome is completed, the next hurdle would be using it to create a viable pup. Archer suggests two possible routes. One way would be to combine the nucleus of a lab-created thylacine cell with an egg of a Tasmanian devil, another carnivorous marsupial, that had its nucleus removed. The resulting embryo could be implanted into the uterus of a Tasmanian devil, potentially resulting in the birth of a thylacine.

Alternatively, Archer said, scientists could try a less direct approach. "A cell line of living Tasmanian devil cells could be used to progressively splice in thylacine sequences to replace the corresponding regions of the devil chromosomes." Repeated over and over again, such a method could eventually produce a thylacine. A 2008 study in which thylacine DNA was successfully spliced into a mouse hints that such a method might be successful.

"I wouldn't want to make light of the challenges involved in any of this," Archer said. Yet he believes such a project may become feasible in the future. "It can't be done now—but that was true 20 years ago for many things that can be done today." Indeed, he said the biggest hurdle for cloning "could be the widespread conviction that it's a waste of time to try." (Related: "Species Revival: Should We Bring Back Extinct Animals?")

Video: Should We Resurrect Extinct Species?

Return of the Passenger Pigeon

Cloning might not be the easiest, or best, route to de-extinction in some cases. If a close relative of a lost species is still alive, researchers can tinker with that genome to "reverse engineer" the extinct species. That's how some ornithologists and geneticists envision bringing back the passenger pigeon.

The passenger pigeon used to thrive in great numbers in North American forests, so abundantly that few people would have imagined the birds' extinction was possible. Their flocks were said to take days to pass by. Sport shooters could easily get scores of them in a single outing. Yet hunting and habitat loss took a severe toll, and the species' population had plummeted by the early 20th century. In 1914, the very last known passenger pigeon died in the Cincinnati Zoo.

Researchers now see an opportunity to resurrect the passenger pigeon from the inside out, using its closest living relative: the band-tailed pigeon.

At the "Bringing Back the Passenger Pigeon" meeting held at Harvard Medical School last year, geneticist George Church proposed sequencing the genomes of both the living and extinct birds and studying the differences. With that information, researchers could tweak the genome of the band-tailed pigeon to create a bird genetically and physically identical to the passenger pigeon.

Perhaps the biggest challenge, as Church noted, would be combining all the desired traits—including behavior—in one bird. Reviving the passenger pigeon, or any other extinct species, would require a comprehensive knowledge of how an organism's genome is translated into anatomy and behavior.

Breeding Cattle Backwards

There may be an even simpler way to revive some lost species, such as aurochs, the ancestors of domestic cows. Aurochs survived alongside their domesticated descendants until the early 17th century, when the species ultimately succumbed to disease, habitat loss, and human mismanagement.

Now, scientists including Henri Kerkdijk-Otten of the Megafauna Foundation hope to re-create the aurochs through a process called "breeding back." Starting with domestic cattle, the process uses strategic mating to incrementally restore the anatomy and the genome of an extinct animal.

The advantage of such an approach, Kerkdijk-Otten says, is that it would utilize cattle already adapted to the world's present ecology, rather than trying to re-create an animal from a different time and climate. "If we start with regional primitive cattle breeds with a lot of aurochs characteristics, we will ensure a cattle breed that is maximally adapted to local circumstances," he said.

A scientifically guided mating program could eventually combine aurochs-like traits from living cattle into one lineage. Some human assistance—such as artificial insemination and embryo transplantation—might be necessary along the way. The goal, Kerkdijk-Otten says, is to get "cattle herds that live wild and independently and consist of individuals with the highest amount of aurochs characteristics possible."

How would researchers know when they had actually recreated an aurochs? By combining information from cattle genetics, zooarchaeology, isotope studies of diet, and even prehistoric cave paintings and rock carvings to "devise a blueprint" of the critical characteristics that make an aurochs an aurochs, said Kerkdijk-Otten.

Ultimately, researchers could also compare the DNA of the new creatures with the original aurochs genome, which is currently being reconstructed.

The Dream of De-extinction

If de-extinction succeeds, a big question looms over any of the methods proposed: What will become of the animals created? Even if lost species can be brought back to life, it doesn't mean they can be successfully returned to the wild.

Kerkdijk-Otten is working with groups such as Rewilding Europe and the European Wildlife Organization to find a place for his project's wild cattle to roam. Likewise, Archer would like to see the thylacine returned to its former range. He views it as a kind of penance: "In the 1800s, we deliberately set out to slaughter as many thylacines as possible. Hence I would argue we have a moral imperative to try to undo colossal disasters of this kind for which we are responsible."

Restoring lost species is controversial, especially when there are so many endangered living species and imperiled ecosystems worthy of scientific attention. Yet there may be points where the two causes intersect. De-extinction techniques might also be used to clone rare species or to introduce genetic variability into species that are at risk of inbreeding because of small population sizes.

"The struggle to bring de-extinction into reality requires far more effort and resources than would be needed to conserve endangered living species," Archer said, "so why not focus on stopping species from going extinct in the first place?"

And in terms of tangible ecological benefits, Archer believes thylacines could kickstart interactions that would benefit other species. Tasmanian devils, the small and carnivorous marsupial cousins of thylacines, suffer from a devastating disease called devil facial tumor syndrome that is transmitted when they bite each other. Archer hopes that reintroduced thylacines would break up Tasmanian devil populations in a helpful way.

"If the thylacine could be put back, it would compete with the Tasmanian devil for food, as it once did," Archer said, therefore "keeping smaller devil populations under control and hence less capable of spreading [the facial tumor] disease across the whole of Tasmania."

For the moment, de-extinction remains a dream. But it's not an implausible one. By combining clues from the past with new techniques, researchers are exploring pathways to re-create species that we never thought we'd see again. The future might contain vestiges of the past.

Editor's note: National Geographic will host scientists and conservationists at the TEDxDeExtinction conference on March 15 at its Washington headquarters, spearheaded by Stewart Brand and Ryan Phelan of the group Revive and Restore. The event will be streamed live on NationalGeographic.com. National Geographic will be reporting on the conference and related debate in coming weeks, including in a cover story in our April issue.

20 comments
Kyle F.
Kyle F.

The whole cloning idea has amazed me for a very long time. At a young age I am just now seeing the goals that can be achieved through cloning. I believe that people are not cloning the endangered species because they can repopulate naturally, however with the species that have been killed off obviously cannot reproduce. This is basically the Tasmanian Tigers, The Mammoths, The Passenger Pigeons, and many other extinct species hope for survival. This their last chance for survival, this is our chance to make things right.

Mitra R. Ramkissoon
Mitra R. Ramkissoon

Well said @Pierrick Buri. Its entirely plausible that mankind would adopt a nonchalant attitude towards conservation if the de-extinction techniques pan out. In the end, I can only hope that nature is the winner.

Pierrick Buri
Pierrick Buri

Dear all, I was wondering if, beyond the technical challenge for cell biologists, we are not sending a wrong message about conservation of endangered species. If it appears to be possible to "de-extinct" a single species, then the argument will come that there is no need any more to protect threatened species and ecosystems, because we could re-create them when we will or need it. This will be an argument to speed up processes such as deforestation, changes in land use and overfishing and then have an tremendous impact on numerous species, already threatened or not, like in a vicious circle !

Jrmy Cmpbll
Jrmy Cmpbll

...this is stupid. true story. why not save the polar bear? why not save the whales? 

...why not fast forward 20 years after we have "revived" mammoths...and they are being "farmed" in china, and then slaughtered in mass for the "healing properties" associated with there eyeballs, and salivary glands??

great story...that gets "intellectuals" who have no grasp on the modern technology at hand, talking about the moral conundrum posed by arrogance, and stupidity.

Dominique Courbin
Dominique Courbin

There are a lot of valid points made here, but I think none of them are sufficient discourage the technological advancements. A million what-ifs as to what could happen when reintroducing species that are extinct, and the impact they could have are logical fallacies. The argument that they could unbalance the stable ecology assumes that the present ecology is natural. In fact, these animals were present first, and any present ecology is secondary to their presence in the first place. Eventually, the field will progress to the point where you will decide if you want your horse to have wings, or your dog to be capable of speech, and have a cat with octopus skin and even legs, but we're not to the point where we can just copy paste genomic expressions. Yet. But, let us assume that we create a new species that ultimately obliterates an entire ecosystem. We will have already demonstrated the two behaviors that are necessary to rectify the issue, 

1) predation to extinction

2) the ability to recreate extinct life, (some of which have been dead for thousands of years.)

So, who cares? If I exterminate all palm trees on the entire planet, but can also recreate them within a year, what does it matter? No matter what we create, it will not be anywhere close to events that we view as natural, ie the asteroid and subsequent ice age. But the knowledge we gain from developing those technologies will be our savior from events that could lead to our own extinction.

Now, give the technology to robots, encase the materials in spores, (through splicing) and then send the biocompilers to far off planets. Why limit our experimentation to our own world?

Stabby L
Stabby L

I am curious how any viable population would result in these cases. Even if they are successful with extracting enough DNA for a few individuals, is there really enough genetic variation to make it worthwhile? We have are having enough trouble with cheetahs and the DNA bottlenecking issues they face, let alone trying to Adam and Eve an extinct species back to life. 


And as much as I think aurochs were amazing creatures, I fear they would somehow end up food, given the human proclivity toward meat eating and relishing anything rare/exotic. 

Pravin Pitchaiappan
Pravin Pitchaiappan

First save the animals around you. Why do you want to wake up innocent species and put them back to grave?

Philip Fortman
Philip Fortman

What about paleontologist Jack Horner's project to retro-evolve chicken embryos by triggering their latent gene for teeth? Can Tyrannus leghorn poultry be in the future?

Emilio Corengia
Emilio Corengia

We are responsible for their extinction in a first place, so sounds like a good idea. For those that we are not, such the Mammoth, sounds like a bad idea.

jonjon jenky
jonjon jenky

this just derails attention and energy away from the true issue that all the other soon-to-be extinct species are facing, such as habitat destruction due to development, over pop of humans, over consumption etc...

 lets forget the technofix and save the f'ng planet ..

Jacqueline Corry
Jacqueline Corry

This sounds like a horrible idea. Think of what happens when we introduce a species into an ecosystem in which it has not adapted. It throws the entire ecosystem off. This sounds to me that it could be as potentially disastrous!

Booster Blake
Booster Blake

We must bring back the mammoth and miniturize it to about 70lbs.  The wild steppes of our living rooms will become it's new habitat. 

Marcos Toledo
Marcos Toledo

Thanks Toth and Kirkland  for thoughs I wonder the attemped reintrduction of the California Condor is going haven't anything of late about that project.

Willie Green
Willie Green

Well if they're going to resurrect any lost species, they should coordinate their efforts to make the expression "as dead as a dodo" become extinct.  Then they can pursue the other critters mentioned in this article.

Andrei Bilderburger
Andrei Bilderburger

I can understand reporters not knowing anything, but why do scientists think that putting a species DNA into another species mitocohondria recreates the first species?  Mitochondria mutate and thus volve much faster than nuclear DNA - they need to also reconstruct the mitochondrial DNA.


Then as Mr. Toth points out, resurrecting the DNA does not resurrect the culture.  Things we've liked to presume are instinctive, like birds migrating and cats grooming, are actually learned.  We don't know what to teach a thylacine, mammoth, or passenger pigeon nor how to teach it.

Alexander Toth
Alexander Toth

James, that's a great point. I'm recalling behavioral components involved with artificial parental care, and that some behavioral macro's need to be "relearned". Does anyone carry the Rosetta Stone for thylacine? I'm sure we'd be able to postulate behaviors... I don't recall much video footage, except for an individual in captivity. 

I don't think one would find many behaviors, besides coping behaviors from confinement. Do we want to show that video to the first viable organism? (This is a silly aside, but sad)

In Oregon, the Columbia Basin Pygmy Rabbit was originally bred for reintroduction in an facility with a hard floor. Upon reintroduction into the wild, they were easy prey (they never "dug" to escape from avian predation). On the second try, they had behavioral modification in a soft floor environment, and were trained to watch out for predators in flight. They did better with reintroduction the second time.


Can we be sure that the Tasmanian Tiger is a good thing to reintroduce at this point? Hasn't the Dingo partly filled it's niche? Species reintroductions can be very tricky. It's difficult to implement the intentions of a project across a whole continent. 

Two instances that need review in regards to AU

1. Cane Toad

2. Feral Camel


---

Would the reintroduction of the Tasmanian Tiger eliminate the phrase "A Dingo ate my baby"?

All it takes is someone to have a "reserve" with a loose gate. Would the long Dingo fence need an upgrade, or an adjustment? 

I would love to read any opinions people have, it seems like many points of contentions could be had from different views. 



James Kirkland
James Kirkland

   Though, as a scientist, I would love to see the giant mammalian fauna of the "Frozen Steppe" resurrected; ethically I have to wonder how these animals will learn the behaviors needed to survive in these environments. Sure, we can raise them in zoos, but much mammalian behavier is not genetically programmed, it is learned; mammals have "culture." 

    In the same way I have little faith in the frozen ark. WE need to keep species alive to teach survival behaviors to the next generation.

Lulu Robinson
Lulu Robinson

@Jrmy Cmpbll I agree with you on mammoths, and we should certainly concentrate on animals that are endangered now, but... I have to admit, even if it's not likely to happen any time soon, if at all, the idea of cloning a thylacine or passenger pigeon is wonderful to me. 

It's our fault that they're gone, after all. Even if we could never conceivably reintroduce them, I think keeping the species alive in some way if we found the capability to do so is something we would owe them.

George Bingham Davis
George Bingham Davis

@Philip Fortman If someone tells you they can resurrect T-Rex, run for your life. Like Ian Malcolm in Jurassic Park said: "Dinosaurs had their shot, and Nature selected them for extinction."

George Bingham Davis
George Bingham Davis

@Jacqueline Corry That would imply that they would just be throwing them at your doorstep. They would be placed in an environment that either they were once in, or one that suited them.

De-Extinction in the News



On Friday, March 15, at our Washington, D.C., headquarters, National Geographic hosted TEDxDeExtinction, a daylong conference on species-revival science and ethics convened by Revive & Restore. The talks are over, but the coverage and conversation continue, in our new cover story on de-extinction, at National Geographic News, on TV—and on Twitter:




More in National Geographic


See exclusive photos and in-depth reporting on de-extinction in April's National Geographic—available as a digital edition March 15 and on print newsstands later this month.

 

National Geographic Channel