A 110-Year-Old Pickled Thylacine Head Helped Build the Most Complete Ancient Genome to Date, Says ‘De-Extinction’ Company

Forgotten for more than a century, a foul discovery in a cupboard at Museums Victoria in Melbourne could be the key to “bringing back” an extinct Australian marsupial, according to researchers from the biotechnology “de-extinction” company Colossal Biosciences. The putrid find? A skinned and pickled head from a thylacine.

“It was literally a head in a bucket of ethanol in the back of a cupboard that had just been dumped there with all the skin removed, and been sitting there for about 110 years,” Andrew Pask, an epigeneticist who leads the Thylacine Integrated Genomic Restoration Research (TIGRR) lab at the University of Melbourne, tells the Guardian’s Adam Morton.

The TIGRR lab has partnered with Colossal since the company announced its thylacine de-extinction project in 2022, an ambitious plan to “bring back” the striped, dog-like animal that humans hunted to extinction, with the last known thylacine dying in captivity in 1936.

Now, the Colossal team claims to have assembled the most complete genome to date of a thylacine, also called a Tasmanian tiger, from the genetic material recovered from the exceptionally preserved head. The biotech company, however, has yet to release scientific evidence to back up its claims. The achievement, along with other related genetic advances, was reported October 17 in a statement from Colossal.

“Our teams are making incredible scientific leaps while on track to de-extinct the thylacine,” co-founder and CEO of Colossal Ben Lamm says in the statement. “We are pushing as fast as possible to create the science necessary to make extinction a thing of the past. These advancements in this project are a huge step forward in that mission.”

“De-extinction” is Colossal’s term for creating a modern-day proxy of an extinct species through gene editing. It doesn’t mean they are literally resurrecting creatures like the thylacine—instead, they aim to edit the genome of a close living relative to resemble that of the target animal, then host that genome in an egg cell from the living species. They plan to develop this genetically edited egg into an embryo, then nurture it to life in a surrogate womb. The resulting animal will be a close approximation of a thylacine—or, in the company’s other de-extinction projects, a modern woolly mammoth or dodo.

At the core of this effort is reconstructing the genomes of extinct animals that haven’t walked the Earth for decades, centuries or even millennia. The discovery of the Tasmanian tiger head provided a crucial tool for its genome construction: RNA, an essential, single-stranded molecule that “reads” DNA instructions to make different proteins. RNA is much less stable than DNA, and thus rarer to recover from old specimens.

Scientists were able to extract RNA fragments from the Tasmanian tiger’s tongue, nasal cavity, brain and eye, per the statement. And since RNA varies within each tissue—unlike DNA—this will give scientists an idea of what a thylacine could taste, smell and see, as well as how its brain worked.

Until recently, some scientists believed building a complete genome from ancient tissue samples to be impossible, Pask tells Live Science’s Sascha Pare. But the team from Colossal has allegedly proven that “you absolutely can get a phenomenal genome from old samples.”

The reconstructed genome is the most complete ancient genome of any species to date, and it is more than 99.9 percent accurate, per the company’s statement. There are currently 45 gaps in the genetic material, but the team hopes to overcome those in the next several months through continuous sequencing efforts.

Still, many scientists remain skeptical about the lack of evidence the company has supplied to back up its claims.

“If we make the claims but they are not peer-reviewed, and they are not approved and they never come to fruition, then it’s a huge disappointment for the entire community,” Parwinder Kaur, founder and director of DNA Australia who has previously worked with Colossal, says to Meg Whitfield of the Australian Broadcasting Corporation. Pask tells the publication that the advancements will be published in a journal as soon as early next year.

In its announcement, Colossal also revealed achievements in assisted reproductive technologies for the fat-tailed dunnart, the thylacine’s closest living relative. The small, mouse-like marsupial’s genome will be edited to resemble the Tasmanian tiger genome, and its eggs are intended to host the edited nucleus. Scientists have not yet figured out how to generate living cells from a genome alone.

The team discovered how to induce ovulation in the fat-tailed dunnart and was able to bring fertilized single-cell embryos halfway through pregnancy in an artificial uterus device—advancements that, beyond the thylacine de-extinction project, also hold important implications for the conservation and captive breeding of living marsupials, Colossal says.

Because there are no other thylacine genomes to compare to the reconstructed genome—just genetic material from other related species—it’s impossible to know exactly how complete these new blueprints are, Michael Le Page writes for New Scientist. Any animal that’s created from it, critics say, won’t technically be a thylacine, and it won’t know how to behave like one.

“It’s more a recreation of some traits,” Emilio Mármol-Sánchez, researcher in ancient genetics at the University of Copenhagen who was on the first team to extract RNA from a thylacine in 2023, tells New Scientist. “It would not be an extinct animal, but a pretty weird, modified version of the modern animal that resembles our image of those extinct animals.”

Margherita Bassi | READ MORE

Margherita Bassi is a freelance journalist and trilingual storyteller. Her work has appeared in publications including BBC Travel, Discover magazine, Live Science, Atlas Obscura and Hidden Compass.