The idea of bringing long lost animals back from the dead might sound like a far off dream, but advances in genetic engineering are bringing de-extinction closer to reality.
At the TEDxDeExtinction event in 2013, the non-profit organisation Revive & Restore partnered with the National Geographic Society to highlight the progress being made in this cutting-edge field. In a series of talks and articles, they revealed the real science behind the fantasy.
Researchers across the globe are examining different methods of de-extinction, and some teams are making real progress towards the ultimate goal of bringing extinct animals back to life. In fact, in 2003, the impossible was achieved – albeit briefly. A Pyrenean ibex was cloned using a frozen skin sample, and it survived for a few minutes after birth, becoming the first animal ever to have defied extinction. This incredible feat has not yet been replicated, and whether it will be able to produce healthy animals is still unknown, but it marked a huge leap forward for de-extinction science. Cloning is fraught with challenges – even clones of living species struggle with a pattern of birth defects and health problems – but fortunately, it is not the only way to revive lost species. Genome sequencing technology and genetic engineering techniques mean that researchers are now in a position to start editing animal genetics, potentially allowing them to rebuild the genomes of extinct animals. At least eight extinct species, including the woolly mammoth, have now had their genomes fully or partially sequenced, and using the genomes from living animals as a map, scientists can pinpoint the locations of different genes.
It is already possible to put genes from one animal into another – this is done routinely in medical research – so researchers are working to see whether they can bring genetic traits out of extinction by inserting them into the genomes of close, living relatives. Researchers are even investigating more traditional methods to bring animals out of extinction. By using selective breeding (choosing to cross-breed animals with specific traits), some teams are hoping to create new animals that look, and behave, like ones that are long-dead.
The idea of de-extinction has been met with a mix of excitement, scepticism, and suspicion. The science fiction version didn’t end well, and the reality of de-extinction research is an ethical and technical minefield. For a start, there are some big scientific challenges that still need to be overcome. Cloning and creating hybrid DNA are both possible, but using these techniques to produce living, breathing animals presents a whole set of biological hurdles. Several teams have had problems convincing the embryos to grow, and perfecting the art of raising a de-extinct animal is going to take time.
Many people are worried that this process will be costly, or even dangerous. There are concerns that de-extinct animals could harm ecosystems, or even bring back long-lost pathogens. The ethics of meddling in genetics and evolution is also a subject of much debate, and whether species would thrive, or even survive, in the long-term is a huge unknown.
Advocates of de-extinction research suggest that the advancements in genetics and evolution will be worth the risks and costs. Bringing an extinct species back to life is one of the ultimate scientific challenges, and success would be a game-changing achievement. The technical and biological knowledge gained in the process could have benefits that reach far beyond the field of de-extinction. Whatever your opinion on de-extinction, there is no need to fear a real-life Jurassic Park. Beth Shapiro, an expert on ancient DNA from the University of California, Santa Cruz, and one of the key scientists involved in the de-extinction work, told Smithsonian magazine that resurrecting the dinosaurs is “not possible”, as we simply don’t have enough of their DNA. So, while de-extinction is inching closer to reality, there is a clear limit on what it will be able to achieve.
DNA is fragile, and the longer an animal has been dead, the harder it is to find well-preserved genetic information. Without access to the full genome, a species really is lost forever. Genetic editing using the genome of a similar species as a guide could produce hybrid animals that closely resemble the original, but it will not truly bring a species back from the dead. A more realistic future for de-extinction research is the restoration and revival of endangered or recently extinct species. Even with access to modern genetic sequencing techniques, the technology behind de-extinction is still a major challenge to be solved before we can truly bring the dead back to life.
On the waiting list
Meet the animals with the best chance of making a comeback
For de-extinction to be even a remote possibility, scientists first need access to well-preserved genetic information. This rules out the dinosaurs and other long-extinct species, but a number of promising projects are underway to revive, restore, or reproduce animals that were lost more recently.
Using a combination of cloning, genome editing, and selective breeding, teams of scientists across the world are getting to work on bringing extinct animals, or at least some of their genes, back to life. These are just six of the projects that are currently underway.
The last of the woolly mammoths died around 4,000 years ago, but thanks to their icy habitat, there are some extremely well-preserved specimens. Dr George Church and his team at Harvard University are trying to revive the species by putting mammoth genes into the DNA of Asian elephant cells.
These modified cells will be reprogrammed to produce stem cells, which will then be used to produce blood cells, hair cells and fat cells. This will allow the effects of the mammoth genes to be studied on a small scale, paving the way to produce a living mammoth/Asian elephant hybrid.
There were once billions of passenger pigeons in North America, accounting for up to 40 per cent of the total bird population, but by the start of the 20th century they were all gone. Professional hunters tore through the population until just one bird was left in captivity in the Cincinnati Zoological Garden. She died in 1914. In 2002, Dr Beth Shapiro and her team sequenced passenger pigeon DNA, and by 2012 they had obtained samples from over 50 different taxidermy birds. Using the genome of a related bird (the band-tailed pigeon) as a map, they are attempting to rebuild the passenger pigeon.
Thylacines, also known as Tasmanian tigers, were hunted to extinction on the orders of the Tasmanian government, and the last individual died from neglect in Hobart Zoo in 1936. Professor Michael Archer and his team at the University of New South Wales are working to restore thylacines to their native home using DNA from a thylacine pup preserved in alcohol in 1866. The soft tissues of the pup are heavily contaminated, but the hard tissues, like teeth, contain untouched thylacine genes. The team are working on ways to insert this genetic information into the genome of the Tasmanian devil.
Professor Michael Archer and his team are also working on a project to revive an unusual species of frog. The gastric-brooding frog incubates its eggs in its stomach; it halts digestion, allowing the tadpoles to develop in safety until they are ready to emerge as froglets. This bizarre Australian species has not been seen in the wild since the early 1980s, but researchers at the University of Newcastle, the University of Melbourne and the University of New South Wales are working together to bring them back. In 2013, they created living embryos by injecting the nucleus of cells from frozen samples into eggs from a related species, the great barred frog. The next step is getting the embryos to grow.
Before cattle were domesticated, wild aurochs were found across the European continent, but by 1627 they had been hunted to extinction. The Tauros Programme, spearheaded by Rewilding Europe, is attempting to recreate this ancient species by cross-breeding primitive domestic cattle. Specialists in Holland, Spain and Portugal are working with cattle breeds from across Europe to find animals with traits resembling ancient aurochs. By cross-breeding different breeds, they hope to be able to recreate entire herds of these large, hardy cattle.
The heath hen was another victim of human appetite. The birds were once found across North America, but by the late 1800s there were only a few left alive. Their last refuge was the tiny island of Martha’s Vineyard in Massachusetts, and despite attempts to save the species, the last individual died in 1932. In 2015, fragments of the heath hen genome taken from museum samples were compared to the genetic code of a close living relative, the prairie hen. Revive & Restore are now leading a project to investigate whether it will be possible to create hybrid heath hen/prairie hen DNA, and later, to repopulate the island with de-extinct birds.
How to bring animals back from the dead
Different methods of de-extinction have different end results. If there are well-preserved cell samples from the extinct animal, cloning could be an option and this would genuinely bring the species back from the dead. However, if the genetic information is fragmented, it might be better to use genome editing. By inserting selected genes from the extinct animal into the DNA of a close living relative it could be possible to create a hybrid animal, bringing extinct traits back to life. Alternatively, if there is a closely related species still living, selective breeding could be an option. By choosing to cross individuals with the right traits, animals could be bred to resemble their extinct relatives.
Engineering the passenger pigeon
Why did you choose the passenger pigeon?
The passenger pigeon was the flagship project of Revive & Restore and I was brought on for my knowledge of the species and my motivation to make this happen. The passenger pigeon afforded a lot of advantages as a starting candidate – we know a lot about its history and habitat needs, there are hundreds of specimens to work with, and a close living relative to engineer. Humans have 8,000 years of experience working with domesticating pigeons, and the eastern United States’ forests have been growing back for 75 years, regenerating their habitat.
What stage are you at in the project?
We are nearing the end of what I’ve deemed Phase One – our genomic research. We’ve laid down foundation work for starting Phase Two, when we will work on actually engineering a passenger pigeon. And we now have committed, pledged, future team members for Phase Three – breeding and introducing birds to the wild.
The project has now gained enough information from genomic research, and the field of avian biotech has advanced enough that we can really flesh out the entire project. The one thing our work hinges on is developing the conditions to grow band-tailed pigeon primordial germ cells in the lab. These are the only cells that will produce breeding lines of birds when engineered and to do this we need to be able to breed band-tailed pigeons efficiently in captivity. We need special breeding facilities for this phase. Breeding and germ cell culturing are the two parts of Phase Two that we are seeking funds for currently.
If science were no object and you could choose any species to resurrect, which would it be and why?
Putting my project species aside and disregarding all of the many considerations that bear down on such endeavours, at the top of my list would be the Choiseul Crested Pigeon. It’s one of the most spectacular bird species to ever live, and also one of the least known and understood, having been observed only once by Anglican explorers. I’d also like to bring back the Dodo bird; it’s the icon of human-caused extinction and another amazing pigeon! Do you see a trend yet? Ultimately, my goal is a future with more life in this world of all kinds, rather than less.
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