After dire wolves, which other extinct species could be resurrected?

A US biotech company's claim to have “de-extincted” dire wolves, made famous by TV's Game of Thrones, has sparked debate over the future of genetics and whether other extinct species could return.

Colossal Biosciences recently announced it had created three pure white canines that represented a revival of the dire wolf, which became extinct about 13,000 years ago. Romulus and Remus, both males, were born in October last year and are now adolescents, while Khaleesi, a female, arrived more recently and is still a pup.

The Dallas company extracted and sequenced DNA from dire wolf fossils, one of them 72,000 years old, and genetically engineered modern grey wolves to resemble the long-lost species.

After editing more than a dozen genes, the company created animals with long, thick, white fur, although some scientists have said the original dire wolves are unlikely to have been such a snowy colour.

Among the many scientific and ethical questions raised by the feat, one perhaps looms largest: what other creatures could be brought back to life through the process of “de-extinction”?

Resurrection plans

Just weeks before showcasing its striking white wolves, Colossal unveiled its “woolly mice”. These mice have been genetically engineered to have coats of long, thick fur.

Using a similar approach to genetically engineer Asian elephants to have long red fur, Colossal hopes to bring back the woolly mammoth. Its other previously announced projects include attempting to recreate the dodo and the Tasmanian tiger.

However, the Colossal Biosciences method – of genetically engineering living species to resemble their disappeared relatives – could ultimately be superseded, William Kunin, professor of ecology at the University of Leeds, told The National.

“There will come a time when you cannot just alter an existing species, but [also] reanimate a lost species,” Prof Kunin said. “What’s being talked about now is a more practical solution in the short term.”

Recreating lost species need not involve creatures from the distant past, as there is also the option to reanimate animals very recently driven to extinction.

Among the species that Brendan Godley, professor of conservation science at the University of Exeter, would like to see living again is the Chinese river dolphin.

It is considered to be the first dolphin species driven to extinction by human beings. For millions of years they lived in the Yangtze River, but none have been since a 2006 expedition to find if any remained proved fruitless.

Ethical challenges

The Chinese river dolphin highlights a key issue around recreating lost species: if they could be brought back, what sort of world would they be returning to?

Such is the scale of destruction of natural habitats that many extinct species would find today’s world no more amenable than the one that caused them to disappear in the first place. “Species go extinct for a reason,” Prof Godley said. “Unless you can correct some of the [causes] that drove them to extinction, there’s no place for them to come back to.”

So, if the Chinese river dolphin were recreated, it would mean dealing with the problems of the Yangtze River, including chemical pollution. Other factors include overfishing of the animals’ prey and heavy shipping activity. “You don’t want to create dolphins to live in captivity,” Prof Godley said.

Similar arguments have been applied to the dodo, because little of its former forest habitat on Mauritius remains.

“If we don't address the reasons and mechanisms species went extinct, we may not see long-term success in bringing back species,” said Dr Manisha Bhardwaj, a wildlife ecologist at the University of Freiburg in Germany. “There are reasons species went extinct, and in many cases the reasons are largely human-mediated.

“These issues challenge existing species and habitats, and may hinder the success of species brought back. We're in the midst of a mass extinction period, and we need to make changes in order for things to improve.”

Importance of diet

The passenger pigeon is another case. There were millions of these birds in North America – they were famed for their large flocks – but they suffered a precipitous decline in the late 19th century because of factors including hunting and habitat destruction. The last living specimen, a bird called Martha at Cincinnati Zoo, died in 1914.

“The passenger pigeon is an animal that was mega abundant, but driven to extinction because it was thought to be limitless,” Prof Godley said. If they were to return, it would be to a world without their primary food source.

“What passenger pigeons ate were chestnuts, and the chestnuts aren’t there,” Prof Kunin said. The passenger pigeon’s main source of food, American chestnut trees, “effectively went extinct because of introduced pests”.

Chestnut blight was introduced from Japan and killed an estimated 3.5 billion American chestnut trees in the first half of the 20th century. Today, the American chestnut is considered “functionally extinct” because saplings usually fall victim to chestnut blight and rarely reach maturity.

Prof Kunin said it “would be amazing” if resistant forms of the tree could be introduced so the species regained its former glory. Indeed, the American Chestnut Foundation is using multiple approaches, including traditional breeding, genetic engineering and blight control to try to help restore populations of the species.

So, in future, it may be a tree from the past, and not just animals such as the dire wolf, the dodo and the woolly mammoth, that graces the planet again.