It had the head of a wolf, the stripes of a tiger and the stiff tail and pouch of a kangaroo. With its dark-rimmed eyes, formidable jaws and staggering 120° gape, the thylacine was once the world’s largest living carnivorous marsupial, until it was driven to extinction around 80 years ago.
If Colossal Biosciences have their way, however, it could be back in less than a decade. This week the US biotech company, which is already working to revive the woolly mammoth, announced plans to de-extinct the thylacine, and reintroduce it to its native Tasmania.
Tasmania was the thylacine’s final stronghold. It disappeared from Australia and New Guinea more than 3,000 years ago. In the early 19th century, European settlers to Tasmania declared the animal a sheep killer and put a bounty on its head. Thylacines were slaughtered in the thousands. The last individual, a male called Benjamin, died at Hobart’s Beaumaris Zoo on 7 September 1936.
Gone, but not forgotten. In the time that has passed, this much-maligned and missed marsupial has achieved iconic status. In its native patch, the Tasmanian tiger, as it is also known, is a familiar face on stamps, beer bottles, T-shirts and the like.
The prospect of ‘de-extincting’ it was first mooted over 20 years ago, after Australian scientists recovered fragments of thylacine DNA from a preserved museum specimen, but it’s taken until now for the requisite technology to approach fruition.
In 2017, Prof Andrew Pask from the University of Melbourne and colleagues successfully decoded the thylacine’s genome; an almost complete genetic sequence that will serve as the blueprint for making the new animal.
The plan is to compare it against the genome of one of the thylacine’s closest living relatives, a small marsupial mouse called the fat-tailed dunnart, and then edit the thylacine-specific sequences into a living dunnart cell. Assisted reproductive technologies, such as IVF and cloning, could then be used to produce an embryo.
So far, so good, but there are a number of issues here. Amongst them, is the fact that the new animal will never be an identical genetic copy of the original.
“There will always be some part of the dunnart genome we cannot replace, like the middle and ends of chromosomes,” says Pask, who is partnering with Colossal Biosciences in the multi-million-dollar project. Similarly, the small portion of DNA that lives outside of the cell’s nucleus, in tiny, energy-generating structures called mitochondria, will still be dunnart. The result then, will be something new; a hybrid animal that is part dunnart, part thylacine.
The prized embryo would then need to be nurtured through its gestation, and beyond. Prof George Church, Harvard geneticist and co-founder of Colossal, is pioneering the development of artificial wombs, but another route is to use the dunnart as a surrogate. Marsupials give birth to lentil-sized babies, so although the dunnart is small, this could be possible.
None of these steps are trivial, but perhaps the hardest part is yet to come, as the inaugural joey figures out how to be a thylacine. Writers who witnessed the wild animals, back in the 19th century, described thylacines as social creatures. Joeys, often born two at a time, stayed in their mother’s backward-facing pouch until they were almost fully grown, and then remained with their parents until the next generation of siblings appeared.
During this time, the family group lived and hunted co-operatively. Genetics will no doubt influence this behaviour, but without a living parent to teach them key skills, no one knows exactly how the first de-extincted thylacines will fare.
The goal is to raise multiple generations, with a healthy smattering of genetic diversity edited in as required, and eventually release them into the wilds of Tasmania, where, it is said, there is still plenty of space for them.
The hope is that that this will have a beneficial effect on the local ecosystem, but this too is uncertain. In its day, the thylacine was an apex predator. It dined on native species, such as wallabies and Tasmanian devils, and helped to keep their numbers in check. In its absence, things have changed. Invasive species, such as rabbits and ferrets, have infiltrated the ecosystem, and the Tasmanian devil has become the island’s largest marsupial carnivore. It’s an unnatural promotion for a scavenging animal, that would previously have stolen leftovers from the thylacines’ table.
Twenty-first century thylacines could help to bring order to this wayward ecosystem. Tasmanian devils are suffering from an infectious facial tumour disease. By removing the sick animals, thylacines could help to keep the disease at bay. By predating rabbits and ferrets, invasive species could be kept under control. The problem, however, is that European settlers were so busy shooting the thylacine, that no one ever properly studied its ecology. Until the new animals are released, no one can say for sure how the ecosystem will respond.
Advocates point out that when wolves were reintroduced to Yellowstone National Park back in 1995, the effects were overwhelmingly positive. Biodiversity rocketed and the ecosystem blossomed. Critics, however, counter that the wolves cause conflict when they steal nearby livestock.
There are some interesting parallels here. Wolves and thylacines are both apex predators. They evolved almost identical skull shapes in response to their shared carnivorous lifestyles. It’s a classic example of convergent evolution, but that’s not all they have in common. The author Ross Barnett, who writes about the reintroduction of large predators in his book, The Missing Lynx, points out that their folklore is convergent too. In Europe, wolves have been mythologised as bloodthirsty, grandma-slaying killers. Meanwhile, down under, thylacines were painted as sly, child-snatching, sheep gobblers.
This slander is misplaced. Wolves don’t kill grannies, and thylacines never preyed on children. It’s now accepted that the Tasmanian livestock industry erroneously blamed the thylacine for its dwindling flocks, rather than face up to its own management failings. There’s no evidence to suggest that thylacines took more than just the odd sheep, but mud sticks.
This is perhaps the biggest challenge to the thylacine de-extinction project. Plans to reintroduce large predators, such as wolves, to areas of their former range, have shown us just how nervy and trigger-happy people can be. In Poland alone, it’s estimated that up to 1,000 wolves are illegally shot every year. If the thylacine is brought back and released into Tasmania, history could repeat itself. The Tasmanian ecosystem may welcome the thylacine back, but only time will tell if people will too.
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