A TEDx conference in Washington last month brought together a diverse selection of scientists who argued that ‘de-extinction’ (bringing a species back to life) is becoming a feasible reality. In our lifetime, we could see species previously confined to the history books roaming the Earth once more, thanks to astonishing advances in synthetic biology in the last decade.
But if it were possible, how would we decide which species to resurrect? Revive & Restore, the organisation championing de-extinction, has drawn up a list of candidate species. There is already talk about introducing a new category to the IUCN Red List of such candidates. But this list is limited by biological factors which determine whether bringing a species back to life is likely to be successful. Species with short life histories and a rapid gestation period have much more potential than other animals, because once restored they could establish large populations more readily. Similarly, we can currently only resurrect species who’s DNA we have a good supply of. This limits candidates to those species which have gone extinct in the last 10,000 years because over longer periods DNA becomes too degraded. Species known to survive despite limited genetic diversity would also make good candidates because they are unlikely to be adversely affected by the inbreeding which is likely to occur at the initial stages of de-extinction.
Other important factors include whether the force that originally drove the species to extinction has been removed. For example, the dodo went extinct firstly because its fearlessness of humans made it an easy target for hunting, and secondly as a result of predation by invasive species on its island habitat. Hunting could be prevented if the species were revived now, and invasive species can also be more easily controlled. Other island birds previously on the verge of extinction, such as the Hawaiian nene or New Zealand hihi, have been successfully conserved from similar threats in recent decades.
Not to be forgotten is the important factor of which species would be most valuable to humans or to ecosystems. The woolly mammoth was an ecosystem engineer in its day. It was partly responsible for the existence of the grassland steppe plains in Eurasia and North America. Since it went extinct, this biome has reverted to tundra and forest, and with the loss of the grassland they maintained, biodiversity in this biome has declined.
Species driven to extinction by the loss of their habitat are less likely to be good candidates for de-extinction. Habitat loss continues to worsen as a result of development, and protected areas are limited by funds and space. Similarly, species that went extinct at the end of the last ice age are unlikely to be successful today, as the climate today continues to warm at an unprecedented rate. Many extinct species lived in habitats that no longer exist at all. We would also need to consider the risk of a reintroduced species potentially becoming invasive pests and potentially dominating over native species established in that area, creating their own conservation problem.
For those that think de-extinction is still a hypothetical concept, you are wrong. Back in 2003, French and Spanish scientists resurrected a wild Pyrenees’ goat species called the bucardo. Originally driven to extinction by hunting, scientists were able to preserve the DNA of the last surviving individual and implant it into embryos of living hybrid goats. Unfortunately the one cloned individual that went to term survived only for a few minutes, as a result of ruinous birth defects. But In the ten years since this event, technology has advanced in leaps and bounds, and scientists are beginning to talk less speculatively and more pragmatically about how to move forward with de-extinction.
There are several potential methods of de-extinction. The bucardo attempt is an example of cloning, whereby DNA was extracted from the species whilst it still lived, copied and reinserted into a related species. The story above highlights its inefficiency and low success rate however. Selective breeding is another technique that involves using a related species to back-breed until its phylogeny or genome carries the characteristics of the extinct one. This is currently being attempted with the extinct European auroch. The third involves genetic engineering, and is likely to be the most favoured method given that most species we want to revive can’t be cloned as they died out before their DNA could be stored. This requires data of the genetic diversity of an extinct animal collected from museum specimens or in well preserved fossils, to put together a picture of its genome. This information can be used to modify a closely related living species’ genome until it mimics that of the extinct one using synthetic techniques.
There is already enormous work being done to bring back the Passenger pigeon using genetic engineering. Once the most populous bird in the world, they flocked in their thousands across North America. Despite their abundance, they were hunted to extinction by 1914. Revive & Restore is currently sequencing the genome of the passenger pigeon’s closest relative, the band-tailed pigeon, whilst also gathering DNA from more than a thousand museum specimens of passenger pigeons. The vast number of preserved specimens is invaluable for allowing scientists to recreate the genetic diversity of the species.
One of the problems with reviving species like the passenger pigeon is that it will be difficult to replicate the social structures they once relied on, because cloning is currently a slow and failure-filled process. It will take time to develop a flock of healthy breeding passenger pigeons in the wild. In addition, since the passenger pigeon went extinct, its original habitat has changed considerably. Its main food was the American chestnut tree, which since 1914 was decimated by blight introduced from imported Japanese chestnut trees. To bring back the passenger pigeon into the world when its staple Autumn food source no longer exists would be futile. However, a scientist named William Powell has been working on a programme to revive and restore the American chestnut species. If this was successful, the outlook for de-extinction of the passenger pigeon would be much more hopeful.
It is not clear how social and cultural behaviours could be revived in de-extinct species. By reviving, you can only ever bring back the physical being. As an example, chimpanzee populations across Africa have devised unique cultural ways of fishing for termites from their mounds. In some areas, chimpanzees use one end of a stick to fish, whereas others use both ends. Similarly, some chimpanzee populations use their hands to remove termites from the stick, whereas others use their mouth. Hypothetically, if you were bringing back chimpanzees from the dead using genetic techniques, you could not also resurrect these cultural behaviours because they have been socially learned through several generations.
De-extinction is worrying for some conservation biologists, because they argue it will divert attention and dilute resources away from currently endangered species. Depending on how it is handled, de-extinction could remove human’s moral responsibility to save animals if there is a belief that extinction is no longer forever, and there will always be a possibility to bring a species back to life.
There needs to be awareness that there are very few species we can actually resurrect. Dinosaurs will never be a possibility because they have been extinct for so long that DNA from fossil specimens is too degraded for synthetic biologists to use. Likewise, some more recently extinct species we know so little about, that even if the technology was able to resurrect them, we can’t predict how they would survive today because we don’t know what they ate or what habitat they lived in. Other extinct species were completely evolutionarily distinct; they have no closely related living species that we could use in order to splice DNA into their genome or to act as surrogate mothers (a woolly mammoth embryo can’t be implanted in a lion for example). Such distinct species have to be dis-counted as candidates for de-extinction and are lost forever. This also heightens the need to conserve currently threatened EDGE list (evolutionarily distinct and globally endangered) species. If these species go extinct, we will never be able to bring them back because they have no living relatives. The conservation of such species should always be prioritised over de-extinction.
Some critics have argued that we shouldn’t be using de-extinction to ‘play God’, by effectively (re)creating species. However, the majority of extinctions in the last 200 years have been caused at least partly by humans ‘playing God’ in altering habitats, climate and by hunting species to extinction. So should it not be our duty to replace them? One thought that concerns me is that all life since the beginning of time has been subject to evolution, with better adapted species surviving selection pressures at the expense of less fit individuals. De-extinction effectively alters the principles of evolution. Species that have died out were often not well adapted to their environment, whether humans put the last nail in their coffin or not. To revive them, possibly using only a small sample of the genetic diversity that originally existed in the species’ genome, turns the whole concept of evolution on its head.
The strongest argument against de-extinction I believe concerns the welfare ethics. As Lori Marino wrote on her recent article over at Kimmela, Dolly the sheep became the only surviving lamb from 30 cloned embryos. Even Dolly was not left unscathed; she suffered from chronic lung disease and severe arthritis as a result of genetic defects, meaning she had to be put down at only 6 years old. The potential for genetic defects is high with de-extinction, particularly where species are being revived using DNA from a limited diversity of extinct individuals. There is a danger that we would create genetic bottlenecks and a high likelihood of inbreeding when first establishing a population of de-extinct species.
Another example currently being talked about is de-extinction of the woolly mammoth. But for this species to be revived, genetically modified embryos would have to be implanted in female elephants. The gestation period would be long, and any complications would not only cause the mammoth individual suffering, but potentially the surrogate elephant mother too. Deaths of elephants for the sake of reviving the woolly mammoth is not an option, when both the African and Asian elephant species are so vulnerable to decline.
These issues highlight the need for there to be ethical guidelines for the humane treatment of cloned species. Jacob Sherkow from Stanford University pointed out that if we were to revive an extinct hominid species such as the Neanderthal, would we treat it as a human? Or an animal? Similarly, if we are reviving a species knowing that it would never be able to be released back into the wild, and would have to spend its life in captivity… is this really something we should do just for the shock and awe factor of having that species in a zoo? Or if we were only able to revive a single individual of a species, is it fair to expect that animal to live on its own in a zoo without a mate, if that species is known to have been a social animal? There are currently no clear guidelines in place for these kinds of scenarios.
So why should we go ahead with de-extinction? Many scientists have pointed out that there is nothing wrong with creating the shock and awe factor that would go with resurrecting a dodo or a woolly mammoth. This kind of ‘cool’ would go a long way for engaging an apathetic public with conservation issues, people would travel far and wide and pay a lot of money to see such species in a zoo. As an aside, they would no doubt also be educated in issues of conservation and extinction whilst viewing a dodo in an enclosure.
There is an argument that ecosystems have been detrimentally affected by the loss of these de-extinction candidates. Stewart Brand from Revive & Restore believes that the passenger pigeon was responsible for modifying their habitat and recycling nutrients. Moving around in their vasts flocks led them to settle in forests, the weight of their numbers breaking branches and encouraging tree recycling andregrowth. Similarly, their numbers helped to release colossal amounts of nutrients into the soil via their collective excretion. Reviving previously ‘keystone species’ could set in motion a rejuvenating trophic cascade that rebalances the diversity of species in an ecosystem, restoring it to its natural glory.
Comparisons have been made with previous restorations of species to their original habitats, such as wolves in Yellowstone. Wolves hunted the elk that had grown in number since its decline destroying the native aspen forests. The sudden reduction in elk after the restoration of wolves allowed these trees to regrow and provide material for beavers to build dams, in turn creating biodiversity hotspots in the river ponds that resulted.
Conservationists are understandably worried that de-extinction will take some of the already limited funding for conservation away. But in reality, de-extinction programmes will be so costly that the whole process is likely to introduce new sources of income and avenues of funding for conservation, because it is mainly being financed by enormous sums of money pumped into the field of genetics.
Professor Kate Jones from UCL and ZSL has argued that conservation biologists should not continue to argue over whether de-extinction is a good idea or not, and rather should accept that it is happening regardless. By doing so, de-extinction creates an opportunity for the conservation and synthetic biology communities to engage with each other, enhancing the potential success of de-extinction by allowing conservationists to advise on how best go about resurrecting species.
The advance of de-extinction technology could create exciting prospects for conservation of species currently on the brink. The genetic techniques being used to revive extinct species can also be applied to living species threatened with imminent extinction. Splicing modified DNA into a genome could be used in the future to make frogs immune to the chytrid fungus decimating their populations worldwide. Similarly these techniques could be used to help bat species currently threatened by white nose syndrome. Synthetic biology has enormous potential to stop the degradation of habitats causing widespread extinction across the globe. For example, if one day we were able to create synthetic biofuels or palm oil, we could prevent habitat loss that that threatens endangered orang-utan populations in Indonesia.
A technicality to consider is that if we manage to one day revive some of the aforementioned species, at what point can we truly say they are de-extinct? Is it the point at which we make the first living clone, even if this individual is the only one of its kind, and unable to breed? If a species can only survive in captivity for the duration of its life, would we still call this de-extinct? To revive all these species we will have to transplant their DNA into living related species. But if we insert auroch DNA into a cow and create a living individual, is this a de-extinct auroch, or just a cow with auroch genes? What really is a species in a world of de-extinction?
De-extinction raises many more questions than it currently answers, and it is clear there is a long way to go before we have a viable breeding population of a revived species in the wild. However, it fills me with excitement that being ‘extinct’ may have a completely different meaning ten years from now. Having seen the advances being made by scientists at the TEDx conference, there is no doubt in my mind that de-extinction will happen in the near future, and I believe it would be a wonderful thing for conservation. However, it needs to be handled with care, to ensure we don’t create new invasive pests, or cause individual animal suffering. Its aim should primarily be to repair the damage caused by humans, and in doing so educate people about the current extinction crisis to inspire them to care and take responsibility for any future species losses.
I welcome your thoughts in the comments below, as de-extinction is an understandably controversial subject! And please vote for the species you’d most like to resurrect in the poll below.
- Scientists clone extinct frog – Jurassic Park here we come? (guardian.co.uk)
- Reviving the Woolly Mammoth: Will De-Extinction Become Reality? (livescience.com)
- Pictures: Extinct Species That Could Be Brought Back (news.nationalgeographic.com)
- Should we bring back extinct species? (futurity.org)
- Reverse extinction: Should we redo the dodo? (phys.org)
- De-Extinction Could Bring Back 24 Different Species: Resurrecting the Woolly Mammoth (scienceworldreport.com)
- Resurrecting Extinct Species Is Conservation’s Next Frontier (blogs.smithsonianmag.com)