Millions of years ago, the Thylacine was widespread throughout Australia. Animals the size of a coyote and has stripes on its body disappeared from mainland Australia about 2,000 years ago.
These animals remained in Tasmania until the 1920s, when they were slaughtered by European colonizers who saw them as a threat to livestock.
"It was a human-driven extinction. European settlers came to Australia and brutally exterminated these animals," said Andrew Pask, a geneticist at the University of Melbourne.
Pask leads a team of scientists collaborating with biotechnology company Colossal Biosciences, aiming to recreate these wolf-like creatures and bring them back from extinction.
Thanks to recent genetic advances, namely the advent of Crispr-Cas9 gene-editing technology, the Thylacine isn't the only extinct species we could see again soon.
Previously, gene editing wasn't sophisticated enough to be able to convert all the different sequences into Thylacine DNA at once. With the millions of edits required, it was assumed that researchers needed to prioritize the most important DNA sequences, resulting in animal genomes that did not exactly match genomes that had become extinct. Pask believes this is no longer needed.
"All of that technology already existed, but nobody had done it on this scale before because DNA editing technology wasn't good enough or fast enough. But now we have the technology, and we have significant investment to try and make this work," Pask said. .
It's not just the Tasmanian tiger that was revived from extinction in this way. Preserved DNA fragments of a woolly mammoth or elephant found frozen in the Arctic tundra, suggest that these large mammals could 'rise from the grave'. To note, most of the woolly mammoths died approximately 10,000 years ago.
Scientists at the Colossal Biosciences lab co-founded by researchers from the University of Harvard, used Crispr to splice bits of mammoth DNA into the genome of the Asian elephant, the mammoth's closest living relative.
The resulting hybrids, known as "mammophants", would be adapted to the cold Siberian tundra, and could help fill the ecological void left by the mammoths when they went extinct. However, there are still technological limitations and obstacles that still need to be overcome.
"Many of the attributes that we have as living animals require multiple different copies of a gene, but it's not easy to tell from a reconstructed genome how many are needed," said Michael Archer, a paleontologist at the University of New South Wales in Sydney, Australia.
"We remain hopeful that a single copy will be sufficient to enable the features sought, but there are other components to these projects," he said.
Another cloned extinct animal
However, genome reconstruction isn't the only method scientists can use to revive animals that have become extinct.
The auroch, a prehistoric breed of cattle, is the subject of ancient cave paintings worldwide. This elephant-sized animal once roamed the plains of Europe. The Aurochs became extinct around the 1600s. Although long gone, the auroch gene can still be found in various breeds of cattle across all continents, especially the breeds in Spain, Portugal, Italy and the Balkans.
Geneticists are currently working to 'rebreed' these species together to produce offspring approaching auroch-like qualities.
Another idea is to clone a dead animal by taking the nucleus from an intact cell, then transferring it to the egg of the closest living relative of the species in the hope that an embryo will form.
However, it takes a complete cell to do this, while cells break down quickly after death. Animals such as the thylacine, which died almost a hundred years ago, cannot be returned this way. At least, this other way could be an option for species that have recently become extinct.
In 2003, researchers succeeded in cloning the Pyrenean ibex, a type of goat that went extinct when the last living individual was killed by a falling tree. Sadly, the newborn died of a lung defect shortly after birth.
Then there's a variation on cloning technology to revive a native Queensland frog species that went extinct in 1983. The creature had a strange method of reproduction, ingesting its fertilized eggs and using its stomach as a kind of uterus.
In 2013, scientists completed the first step of transferring the nucleus from a frozen frog cell into the empty egg of a closely related amphibian. Amazingly, the cells began to divide and an embryo was formed.
"We did it hundreds of times and it didn't work, then suddenly one of them did and we saw these hybrid embryos start dividing under the microscope and it was really exciting," said Archer.
Unfortunately, this joy did not last long. The project was halted when none of the embryos developed into tadpoles or frogs.
"The frog embryo develops into a ball of cells, which is normal embryonic development, but then stops. Normally the outer layers of cells are folded and there is a two-layered structure that leads to the tadpole, but we didn't do that," said Archer.
The same thing happened when the team tried to create embryos with two living frog species, showing that it was an aspect of their experimental work that interfered with the development of the embryos, not a problem with extinct frog DNA.
"We are working to find out what the bottleneck is in these living frogs before we can get back to the DNA of animals that have become extinct," said Archer.
Impact on the ecosystem
Reintroducing mammoths and thylacines could disrupt existing ecosystems. As these animals became extinct, others would evolve and adapt to take their place. Will this organism suffer as a result?
Thanks to climate change, the environment these creatures once lived in may have changed drastically. Some of the plants the woolly mammoths ate are also long gone. Would mammoths still be able to survive on their own in the wild, and if not, who would look after them? Will they end up as animals that inhabit the zoo?
"I don't think we have to return all the animals. I think it has to fit certain criteria," said Pask.
"For the Tasmanian tiger, this was a recent extinction event, so their habitat in Tasmania is still there, all the food they used to eat is still there, so there is a place for them and they can thrive again in that environment," he explained.
He added that the Thylacine also played an important role in the ecosystem because it was an apex predator so it sat right at the top of the food chain. There were no other marsupial apex predators besides the thylacine, so when it went extinct it left a huge gap.
Some researchers argue that efforts to bring back long-lost species may reduce conservation efforts to save existing animals and even increase the risk of loss of biodiversity.
"This technology is not just about bringing the Thylacine back to life, it's about preventing other animals from going extinct," Pask said.
He continued, Australia is experiencing too many bushfires in Australia, and with increasing global temperatures, they are facing more severe weather events in the coming decades.
What Australia has done is collect tissue from marsupials in the most at-risk areas and freeze them. This means, in the event of a bushfire, once the vegetation grows back, humans can repopulate the area with the same species.
Meanwhile, Archer agrees that moral rights outweigh any wrongs. "I think it's unethical not to do it. I think the ethical issue here is that it's human impropriety to make these animals go extinct. It's not about playing God, it's about playing smart humans by preventing what we do," he concluded.