Mar 14 2022

De-Extinction of the Tasmanian Tiger

The last known thylacine, commonly known as the Tasmanian tiger, was in captivity in 1936. This marsupial predator was wiped out by human hunting. At the time Europeans colonized Australia the range of the thylacine was limited to Tasmania, but it did not survive contact with Europeans for very long.

The thylacine is now one of the primary targets for de-extinction – literally bringing the species back from extinction using cloning technology. This effort has just received a significant boost. The University of Melbourne just received a $5 million grant to develop their Thylacine Integrated Genetic Restoration Research (TIGRR) Lab. Scientists love their clever acronyms, and I wonder how long they had to work on this one.

The researchers at the lab have a specific plan in terms of how to bring back the thylacine. They have already completed the first step, which is to completely sequence the thylacine genome. Now they need to study this genome to understand it as best as they can. They will need to synthesize a complete genome, and then place it in stem cells prepared from another marsupial. This is where the cloning process comes in. You remove the DNA from the stem cell, insert the new DNA, and then coax the cell into dividing to form an embryo. They then plan to implant the embryo into a living host, such as a Tasmanian devil, who will then give birth to a live thylacine.

The process is tricky. We have cloned large mammals before, but not of an extinct species. Also, the process is not done when we have one thylacine. The goal is to create a breeding population. That means we need many individuals, both male and female, with sufficient genetic diversity. Once they have established a breeding population in captivity, the ultimate goal is then to reintroduce them back into the ecosystem of Tasmania.

This last bit is why so much attention is being focused on the thylacine for de-extinction. One of the criticisms of the concept of de-extinction is – what will we do with the animals once we have cloned them back into existence? I think we can reject the simplistic thinking, expressed by Dr. Ian Malcolm in Jurassic Park, that extinct animals were somehow “meant” to go extinct. This is sometimes expressed as the very vague notion that de-extinction is not “natural”. More thoughtful concerns regard where the animals would live. Regardless of how or why they went extinct, the ecosystems they once inhabited may no longer exist. They have moved on, adapted to a world without them. We should not simply reintroduce new creatures into a natural ecosystem without concern for the consequences.

But the situation with the thylacine in perhaps unique. They fairly recently went extinct, and the Tasmanian ecosystem is largely unchanged since that time. They can simply be reintroduced and take up where they left off. In fact, researchers feel that the ecosystem will benefit from their presence. The same may be true for other recently extinct species, say within the last century or two. If we reintroduced the bluebuck antelope, the ivory-billed woodpecker, or the great auk, I doubt this would be disruptive to the ecosystem. It is possible, perhaps even likely, that reintroducing a recently extinct species may be less disruptive to the ecosystem than their extinction in the first place.

There are therefore many animals on the recently extinct list that could be safely reintroduced after de-extinction. There is also the possibility of creating natural refuges for some animals. New Zealand is engaged in a long term project called Zealandia (which I visited when I was in New Zealand and is very cool). This is a walled-off natural refuge where species introduced to the island are carefully excluded, especially predators such as cats, rats, mice, and possums. Their goal is to slowly return Zealandia back to the way the island’s ecosystem was prior to European arrival, or even any human, arrival. Perhaps if we can de-extinct the moa they could be introduced into this protected ecosystem. There is no reason why the Zealandia experiment cannot be replicated elsewhere.

The farther back in time the extinction took place, however, and the larger the extinct species is, the more controversial re-introduction becomes. The iconic species highlighting this problem is the woolly mammoth, which went extinct about 4,000 years ago (or longer in different ecosystems). The ecosystems in which the woolly mammoth lived no longer exist. So, where would we put them? They are giant, need lots of food and space, and cannot easily be absorbed into an environment.

Again, I think it’s possible to make a refuge that could include a population of woolly mammoths. Short of that, they would have to live in captivity. That concept remains controversial – should we de-extinct a species that is destined to live only in captivity? Of course the dividing lines between a zoo, a park, and a refuge are blurry. Whatever you call it, there would need to be a large habitat where the animals could roam. One key difference is that in a zoo or park food would have to be provided, where in a natural refuge the animals would find food out in the environment. In any case it is reasonable to conclude that the animals could be happy if they had a large stress-free space in which to live.

There are also scientific benefits to de-extinction programs. They would necessarily involve learning a great deal about genetics and biology, the technology of cloning, and we would learn more about the species we de-extinct. Advances could also be used to prevent extant but endangered species from going extinct. We don’t have to wait until they are completely gone to improve their population and genetic diversity.

No responses yet