A radical idea to support the recovery of damaged ecosystems has been gathering steam: resurrect species that have gone extinct and reintroduce them to the wild. Proponents of “de-extinction” argue that by returning species that played an important ecological role to their old habitats, entire regions could benefit.
The lab-created animals would not be the exact species that went extinct, but hybrids of those species with their DNA filled in by living relatives. The most well-known de-extinction project is an effort to bring back a version of the woolly mammoth by splicing its genome with Asian elephant DNA. The work has been a longtime project of Harvard geneticist George Church, who recently co-founded the bioscience company Colossal, with $75 million in private funding, to accelerate the research.
Today Colossal announced that it has partnered with a group of researchers at the University of Melbourne to work on the de-extinction of another animal: the thylacine, also known as the Tasmanian tiger. This Australian marsupial predator went extinct less than a century ago.
“We’ve been working on [thylacine de-extinction] for about 10 years in my lab, but by partnering with Colossal, they have this incredible wealth of knowledge, this incredible amount of technology that they can bring to the table with the work that we’ve been doing,” says Andrew Pask, head of the thylacine restoration lab at the University of Melbourne.
The scientists behind the project believe that bringing the creature back would restore ecological balance to the island of Tasmania by re-introducing a top predator that kept other animals in check. The work could also help develop technology, such as genetic engineering tools and artificial wombs, that could support other conservation work.
But skeptics argue that the genetic engineering challenges that have thwarted previous attempts to bring back the thylacine still present significant barriers, and that de-extinction work could distract from other conservation efforts to help the animals facing extinction now. The ethics of bringing back an extinct creature are also hotly debated.
“I don’t see any difficulty in slotting the thylacine back into modern ecosystems. There’s a space still waiting for the thylacine,” says Chris Johnson, an ecologist at the University of Tasmania who studies extinction. “But we’ve been through this before. Thylacine de-extinction has been a topic in Australia for at least 20 years, and it’s gone nowhere.”
A lost Australian predator
The thylacine (Thylacinus cynocephalus) was a marsupial, carrying its young in a pouch just like a kangaroo—Thylacinus comes from the Greek word thulakos meaning pouch—but it looked more like a slim dog with a stiff, thick tail. The animal was nicknamed the Tasmanian tiger for its characteristic striped lower back. It roamed the Earth for millions of years, likely since the early Pleistocene epoch, ranging across much of Australia and New Guinea.
Semi-nocturnal and mostly solitary, thylacine was likely an ambush predator, hunting small- to medium-size prey at night. Sometime in the last few thousand years, however, the animal disappeared from New Guinea and the Australian mainland, likely due to human hunting and competition with the dingo, which was brought to Australia from Asia some 4,000 years ago. For hundreds of years, the animal clung to the island of Tasmania as its final refuge.
The last known of its kind, a thylacine named Benjamin, died in September 1936 at the Beaumaris Zoo in Hobart, Tasmania, just two months after its species was granted protected status. Several people have since claimed thylacine sightings, and some researchers have argued the animal could have survived longer than thought. No confirmed sightings have occurred since 1936, however, and the species was declared extinct by the International Union for Conservation of Nature in 1982.
Today Tasmania’s ecosystems are threatened due to the disappearance of its “tiger.” The loss of an apex predator has left an over-abundance of small macropods, a family of marsupials such as red-necked wallabies and Tasmanian pademelons. These animals have damaged local vegetation through over-grazing, creating ecological instability and threatening other herbivores.
Bringing the thylacine back could, in theory, help keep these smaller animals in check. Apex predators also help curb the spread of disease among their prey, such as devil facial tumor disease, a transmissible cancer currently spreading among Tasmanian devils. But resurrecting a species from extinction presents major scientific challenges.
Genetically engineering an extinct creature
Any de-extinction project needs to start with the closest living relative to the animal in question, Pask says. The thylacine’s closest living relative is the numbat, a small insectivorous marsupial native to Western Australia whose genomic sequence was decoded earlier this year.
Numbats and thylacines shared an ancestor some 40 million to 35 million years ago, and the two species share up to 95 percent of their DNA. The numbat’s genome could therefore serve as a template that, using gene editing technology like CRISPR, could be tweaked to resemble the genome of the extinct thylacine, which was first sequenced in 2017 using museum samples.
“We’re very good at synthesizing large fragments of DNA, so we genetically engineer that living [numbat] cell now to turn it into a thylacine genome,” Pask says. “Then you just have to turn that cell back into a living animal.”
The available thylacine genome is fragmentary, however, and filling in some of the gaps remains a challenge. It could be more complex to genetically engineer a proxy thylacine than a proxy woolly mammoth, for example, because the latter is more closely related to its living mold, the Asian elephant, than the thylacine is related to the numbat.
Efforts to bring back the thylacine do have an advantage though, Pask says, which is that the animal’s extinction was relatively recent. Scientists have a comprehensive biobank of information on the species as well as museum and laboratory samples, including skulls, skeletons, scat, and even preserved embryonic young originally found in their mothers' pouches.
Tom Gilbert, a geneticist at the University of Copenhagen who is not involved in the thylacine effort, believes de-extinction is an intriguing idea and can benefit research, but he is skeptical about the practicality of the work. Earlier this year, Gilbert’s team published a study about its attempt to recover the genome of the Christmas Island rat, which went extinct in the early 20th century, by using the genome of the closely related Norway brown rat as a template.
Even with biological samples of the Christmas Island rat and a high-quality genome from a similar species, nearly five percent of the extinct rat’s DNA was impossible to fully recover. That much missing genetic information would make de-extinction efforts difficult, Gilbert says, and any resurrected animals could differ significantly from the original species.
“The numbat is no way near like a thylacine,” Gilbert says. “They’re changing the numbat to make it more thylacine-like.” And filling out missing genetic information, he says, would involve making decisions about how to modify the animal. “Ultimately you are forced to be extremely biased in what you choose to change.”
One of the risks, Gilbert says, is that those changes could make the animal poorly equipped to survive in the wild.
Born in a lab
Even if these genetic engineering challenges can be overcome, successfully bringing an animal back through de-extinction would require growing a baby animal from a viable cell. The technology to do this for the thylacine doesn’t exist yet, but it could prove easier than with the woolly mammoth, which has a gestation period of 22 months. A thylacine is far less daunting by comparison, developing after a month in the womb and another 12 to 16 weeks in the pouch.
For over a year now, Colossal has been working on two different devices for the gestation of the thylacine: an artificial womb to bring the embryo to a fetus, and an artificial pouch to go from a joey to an independent cub. “Neither one of them are complete, but you know, we’re just making steady progress on them right now,” says Ben Lamm, co-founder and CEO of Colossal. Surrogacy, or having another animal host the embryo, is also a possible solution.
If everything works as intended, it would still take years for proxy thylacines to come out of the lab. Lamm doesn’t have an available timeline, but he thinks the project might be speedier than the woolly mammoth effort, which will require at least six years.
Once developed, Lamm says, this technology may have several applications. Developing artificial gestation and maturation devices could help in the conservation of other endangered marsupials, like repopulating the koalas killed by forest fires in recent years.
Michael Archer, a paleontologist specializing in Australian vertebrates at the University of New South Wales, led an effort to de-extinct the thylacine back in 1999, but the project was cut short because the sample DNA was too degraded. Although he is not involved in Colossal’s new effort, Archer is enthusiastic about the project.
“I am delighted, of course, to see that another person shares my same conviction, and we should be able to do this when technology catches up with imagination,” Archer says.
Will Tasmania want the thylacine back?
When a top predator like the thylacine disappears, its ecosystem can plunge into “cascading trophic downgrading effects.” The extinct animal’s prey becomes overpopulated, wreaking ecological havoc and resulting in a vicious cycle of destabilization and decline.
Projects such as the reintroduction of wolves to Yellowstone and the Tasmanian devil to Australia have proven successful ways to stabilize ecosystems. Proponents of bringing back the thylacine say it can do the same for the Tasmanian bush.
“It’s a glove that’s missing a hand, and if the thylacine could be put back into that situation, it would slip back into that glove as if it had never been missing,” Archer says.
But some researchers are not convinced that de-extinction is a practical way to promote conservation and ecosystem health.
Chris Johnson, the ecologist at the University of Tasmania, says that if there were a thylacine to reintroduce into the Tasmanian wild right now, it would indeed benefit the ecosystem by controlling the over-abundant populations of small and medium-size marsupials. However, he sees the project as “very, very, very difficult” and says that there are other, more realistic ways to promote ecosystem recovery across the entire country.
Reintroducing the thylacine to the Australian mainland probably wouldn’t improve ecological balance, Johnson says, because environments there are being harmed by invasive species such as foxes and deer that are likely too fast for the thylacine’s ambush tactics.
“If we want to restore the ecological function of a top predator to mainland Australia, the approach that is simplest and, on the evidence most effective, is to look after the top predator that we currently have, which is the dingo,” Johnson says.
While de-extinction efforts could advance bioengineering technologies, it remains unclear how much they will contribute to conservation—and whether bringing a version of an extinct animal back can be done in an ethical way.
Reintegrating the thylacine into its habitat would be an effort carried out in unison with local conservation groups and Aboriginal communities, Lamm says. “The thoughtful reintroduction of species will probably take longer than the actual creation of the animals, just because we want to ensure that it’s done the right way,” he adds.
But this technology is an example of a colonial mindset, says Emma Lee, a professor at the Swinburne University of Technology in Melbourne who specializes in Indigenous affairs and environmental management. An Aboriginal trawlwulwuy woman from Tasmania, Lee sees de-extinction as the “wrong approach” and one that “obscenely steals from Tasmanian Aboriginal people the right to speak for country,” particularly considering overhunting by European settlers is considered the primary reason the thylacine was eradicated from Tasmania.
“Our culture and animals are not their scientific playground,” Lee says.
Pask says that “all future rewilding efforts would engage current Indigenous landowners,” and to him, bringing the thylacine back after humans drove it to extinction is an obligation. “I would like to think that if we have the tools to correct these actions, which we now do,” he says, “we owe to these species to try to restore them back to those ecosystems.”