We are living in the midst of a mass extinction event known as the Holocene extinction. In 2002, the prominent biologist E.O. Wilson estimated that half of all higher organisms could be gone by the year 2100. A 2014 study estimated that animals and plants are disappearing at 1000 times the normal rate. It is largely because of our technological progress that we have been able to alter the climate and exterminate hundreds of thousands of species. However, new tools are now being developed that can help us save species on the brink of extinction, or even bring back those we had thought lost forever.
Candidates for resurrection
Any species that went extinct in the past 100,000 years is a potential candidate for resurrection. This includes prehistoric animals such as the four ton giant ground sloth, the Irish elk with antlers measuring 3.65 metres across and the iconic woolly mammoth, as well as more recently vanished creatures such as the dodo bird and the passenger pigeon.
De-extinction can be achieved by three different methods: cloning, back-breeding, and genome reconstruction. Cloning was tried in 2003 when DNA from the last Pyrenean ibex was implanted into the egg cells of an ibex-goat hybrid surrogate parent. It took 60 attempts for one live birth and the resultant ibex died within minutes due to congenital lung defects. This failure did not come as a complete surprise as cloning by this method has a low success rate, even when conducted using intact DNA and with the same species as the surrogate – many embryos were lost in the making of Dolly the sheep.
Back-breeding refers to taking a domesticated organism and selectively breeding for the traits of its wild ancestor. This method is being used by the TaurOs project to bring back the extinct Aurochs (a type of large wild cattle). Back-breeding has the advantage of being cheap, however it is slow and only feasible when the genes of an organism have been diluted but not lost. This makes it suitable for all the ancestors of domesticated organisms and some species which interbred with other extant species before going extinct. As a result we could in theory use back-breeding to produce Neanderthals from human populations with Neanderthal ancestry, equally they could be brought back using the most state of the art method of de-extinction: genome reconstruction.
Genome reconstruction is currently being explored as a means to resurrect the woolly mammoth and the passenger pigeon. In the past decade there has been an explosion in our capacity to sequence (read) DNA at low cost, now we can even sequence the DNA of organisms that have been extinct for thousands of years. Of course, knowing the DNA sequence of an extinct organism does not give us an extant organism. In order to use this information for the purposes of resurrection biology one needs two things: a living species that is as closely related to the extinct species as possible; and the means to edit the genome of that species.
Many extinct organisms have left behind closely related cousins. The woolly mammoth and the Asian elephant are more closely related to one another than the Asian and African elephants, suggesting that they would be able to produce live offspring. Genome editing has been made possible by a technique known as the CRISPR/Cas system.
This system evolved in bacteria to grant them immunity from the dangers of viral DNA, but it has been adapted to allow the rapid deletion and insertion of DNA in target cells. The Harvard geneticist George Church has already inserted genes for longer hair growth, cold resistant blood and extra fat tissue into Asian elephant stem cells. An Asian elephant with these features could be born in this decade. Through selective breeding of such elephants and the continued addition of ancient DNA, the herd would become more mammoth than Asian elephant. This use of back-breeding with genome reconstruction is prudent as genome editing is in its infancy and there is a risk of incompatibility between cow and calf.
Genome reconstruction and cloning can also be applied to prevent extinction as opposed to reversing it. Critically endangered species such as the Gaur and Mouflon have been successfully cloned; however these animals have yet to produce offspring of their own. Genome reconstruction offers us the opportunity to introduce genetic diversity into a species that has lost much of its own. For endangered species this could mean the difference between complete recovery and population collapse as a result of inbreeding.
De-extinction has been the stuff of science fiction since Jurassic Park was written in 1990; it is now becoming a reality. The dinosaurs (excluding birds) are not viable candidates for de-extinction as their DNA has degraded over tens of millions of years. Instead, we are presented with the opportunity to resurrect species which were exterminated by us and our ancestors.
The question remains: is this a good idea? Have ecosystems moved on since these animals died out such that they could not be successfully reintroduced? Could these creatures be taught behaviours that were passed on for countless generations and then abruptly lost? Some conservationists consider de-extinction a frivolous expense that distracts us from preventing extinction in the first place. Others fear that invalidating the slogan ‘Extinction is forever’ will reduce the pressure on people and policymakers to protect endangered species.
When grey wolves were reintroduced to Yellowstone National Park after almost a century of absence, elk were forced to abandon valleys where they were vulnerable. As a result shrubs and willows were able to take root on riversides. Bears and beavers benefited from the new vegetation, which also had the effect of increasing silt deposits from the river, changing its shape over time as more bends were introduced.
There is now no doubt that these effects and others benefitted the park’s ecosystem. Resurrection biologists hope that bringing back extinct species would have similarly positive results. No doubt this would depend on the species being resurrected, which brings us back to the mammoth. Mammoths survived for millions of years through constantly changing climates. As is often the case for large animals, the fossil record shows that mammoths were less sensitive to subtle environmental changes than smaller specialist species. Today the Eurasian steppe ecosystem favoured by mammoths is far less densely populated than the habitat of the endangered Asian elephant.
It has even been suggested that mammoths could extend the steppe ecosystem further north by removing trees that compete with a variety of grasses, this would have the effect of suring up the Arctic permafrost which stores two to three times as much carbon as the world’s rain forests and is currently eroding at an alarming rate.
When it comes to the lost behaviours of the species, mammoths are again good candidates. The gradual transition from Asian elephant to mammoth will allow the developing species to gradually learn what extra skills it needs as it is guided north over the generations. It is hard to determine whether or not resurrection biology will serve as a distraction from conservation biology. Certainly we can expect the cost of bringing back an extinct organism to continue plummeting as the technologies needed are developed for research and medicine, but what of the threatened status of permanent extinction? My hope is that excitement and optimism generated by responsible de-extinction will outweigh any lethargy it could facilitate. Flagship species such as the Siberian tiger already drive conservation efforts as their survival necessitates the protection of their entire ecosystem. Surely resurrected species such as the woolly mammoth would serve as powerful flagships.
Finally, there is the less tangible objection that bringing back an extinct species equates to ‘playing God’. This is a vague complaint which is perhaps unsuited to dialogue in a secular society. Strangely environmental destruction and extinction are not considered playing God, perhaps because these acts are more familiar and less purposeful. Nonetheless these acts have permanently altered our planet and continue to do so. Regardless of one’s religious beliefs it is clear that we are not passive creatures on God’s earth whose only responsibility is to avoid interfering with his or her or their plan. We are the most powerful force of agency on this planet and not only must we stop destroying it, we have to decide what the reconstruction will look like. I for one think that every tool at our disposal should be used build the wild anew.
Illustration: Maria Kavanagh