How Science Plans To Bring The Tasmanian Tiger Back From Extinction

There are many reasons why plants and animals go extinct, but in the case of Australia's thylacine, also known as the Tasmanian tiger, it was down to simple human intervention. The animal, which could reach 6 feet long, tail included, was not a tiger at all, but a carnivorous marsupial that, like kangaroos, raised its young in a pouch. The tiger moniker came from the fact the creature had a series of dark stripes running down its back, though its overall physiognomy more closely resembled a wolf — hence the creature's other nickname, the Tasmanian wolf. 

By the early 20th century, the thylacine had died out on mainland Australia, but remained on the island of Tasmania, where it was seen as a threat to farmers and their livestock. As such, the Tasmanian government paid bounties to trappers and hunters, who effectively drove the species to extinction. The very last Tasmanian tiger is thought to have died at a zoo in Tasmania's capital Hobart in 1936. 

Ever since, there have been numerous claims of Tasmanian tiger sightings on the island, and even research projects set up to try to determine if the mysterious animal still dwells somewhere in Tasmania. Despite these efforts, however, the thylacine remains officially extinct. But scientists are working on a remedy to that problem.

Efforts to bring the Tasmanian tiger back from extinction have been ongoing for some time. In 2000, palaeontologist and then-director of the Australian Museum, Mike Archer, announced his plans to clone the thylacine using extracted DNA from a preserved specimen — prompting some incredulous reactions from many of his peers. The project was intended to produce a real-life Tasmanian tiger within 10 years, yet funding issues and the discovery that the thylacine DNA has been contaminated with human DNA meant the ambitious project never completed its goal.

But the project did make some important steps in the overall effort to resurrect the Tasmanian tiger. As part of their work, Archer's team managed to extract genes from the specimens with which they were working, thereby helping in the larger effort to reconstruct the thylacine's genetic code. 

Since Archer's project wrapped up without producing a Tasmanian tiger, further efforts have been made to return the legendary animal to its native land.

There are many organizations fighting to prevent animal extinction, but there are also groups looking to reverse extinction altogether. One of them is Colossal Biosciences, which describes itself as a company committed to fighting — and potentially reversing — extinction. In 2022, the company announced its thylacine de-extinction project, which essentially aimed to bring the carnivore back to life and return it to its native Tasmania. Using well-preserved thylacine samples as a reference, Colossal aimed to reconstruct a complete Tasmanian tiger genome — the entire set of DNA instructions found in a cell. Aside from achieving what would be a remarkable scientific feat by ressurecting the extinct creature, the project also aims to help bolster the local ecosystem by fighting against biodiversity loss which can be severely affected when something in a food chain goes extinct.

In October 2024, Colossal Biosciences revealed they'd made a major breakthrough in their effort to resurrect the thylacine. The company announced that it had managed to create a version of a thylacine genome that was more than 99.9% accurate. In a press release, Colossal characterized the advancement as "record-breaking," explaining how their thylacine genome has been constructed "to the level of chromosomes." The challenge will now be for the scientists to find the remaining 45 missing pieces, which Colossal estimates will be closed in a matter of months by more sequencing efforts.

How exactly was Colossal able to create such an accurate version of a thylacine genome? It's all about the existence of well-preserved specimens, which scientists were able to use as a reference point. Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) both carry genetic information, but most specimens of extinct animals do not contain enough of either to be useful when it comes to reconstructing a genome. RNA in particular is much less stable than DNA, making it much harder to find in preserved historic specimens. What's more, as Colossal points out in its press release, RNA varies within each tissue, whereas DNA is the same in almost every nucleus in every cell of the body.

In the case of the thylacine, however, Colossal capitalized on the unusually well-preserved long DNA sequences in the specimens available to them. Perhaps more crucially, the group was able to find long RNA molecules in preserved soft tissues from a 110-year-old Tasmanian tiger — specifically, a complete adult thylacine head that had been skinned and preserved in ethanol. Colossal was therefore able to take RNA from multiple tissues, including the tongue, nasal cavity, brain, and eye. This allowed the scientists to understand what the thylacine could taste and smell, as well as gain an insight into its vision and brain function.

As well as constructing a remarkably complete version of the thylacine genome, scientists are also comparing the extinct beast's genome to those of wolves and dogs in order to identify specific aspects that differ from other species. In particular, the Colossal team is aiming to determine the genes that produce the thylacine's distinct jaw and skull shape by comparing the thylacine, wolf, and dog genomes and identifying areas of the genomes that are evolving more quickly, which they refer to as "Thylacine Wolf Accelerated Regions" or TWAR in their press release.

These were then used to conduct experiments in mice that proved the TWARs were indeed responsible for driving the specific morphology of the skull and jaw. Ultimately, these genetic traits were edited into the cells of a fat-tailed dunnart, a mouse-like marsupial that is the closest living relative of the thylacine. This is where CRISPR technology comes into play, which essentially amounts to using molecular scissors to edit DNA. Colossal plans to use fat-tailed dunnarts as surrogates for thylacine embryos which contain these edited genomes in the future.

Using dunnarts to host edited thylacine genomes throws up its own set of unique challenges, with scientists having to develop a method for inducing ovulation in a dunnart, allowing them to control when the animal goes into heat. The eggs that are produced as a result will then be used to create new embryos, and those will ultimately host the edited thylacine genomes.

Alongside this process of inducing ovulation, Colossal has also been able to take fertilized single-cell embryos and maintain them in an artificial uterus to over halfway through pregnancy — longer than any other attempt to grow marsupial embryos in an artificial uterus.

As these efforts continue to become more sophisticated, the prospect of bringing the Tasmanian tiger back from extinction becomes increasingly realistic. Which, considering just 20 odd years ago many scientists scoffed at Mike Archer's plans to do so, is a significant feat in and of itself.