Earlier this month, scientists announced they had extracted RNA from the remains of a thylacine, aka the Tasmanian tiger.

The RNA may be tiny, microscopic even, but the ramifications of this extraordinary success are significant for ‘de-extinction’ efforts.

Bringing back species that have disappeared has long been a fascination for scientists – and science fiction writers – but progress has been slow, in part because DNA is only part of the story.

It was almost 40 years ago, in June 1984, that researchers from the University of California at Berkeley announced they had extracted DNA from ‘a scrap of dried muscle tissue’ from the remains of a quagga, an extinct subspecies of the modern zebra. 

In the decades since, those vital building blocks of life have been extracted from myriad long-lost species, from mammoths and aurochs to extinction’s ultimate poster child, the dodo – and even our own relatives the Denisovans, although no one is suggesting resurrecting ancient humans.

However, to truly bring back an extinct animal, DNA is not enough. 

DNA, or deoxyribonucleic acid, is the body’s blueprint. DNA in cells contain all the information required to build an entire individual, coded in chromosomes. But to do so, they must specialise and form particular types of cell, a process known as gene expression – and this is where RNA, or ribonuceleic acid, comes in. 

It is the architect, transforming those plans into a living creature. 

And now, Dr Emilio Mármol Sánchez and his colleagues have extracted, sequenced and analysed RNA from the 130-year-old remains of a Tasmanian tiger.

The feat is not an easy one, given RNA molecules are much more fragile than DNA, sometimes thought to begin decaying within hours of death.

Now it has been proven possible, recovered, ancient RNA could supercharge de-extinction efforts.

But – and it’s a big but – there are still questions to answer before bringing back a species from the dead, aside from the many other momentous scientific steps required.

Firstly, a philosophical one. If a mammoth was born to a modern elephant, would it know how to behave like a mammoth? Or would it behave like a hairy elephant? 

With no other members of their species to learn from, and being born into a very different world from the one they evolved and lived in, any resurrected species are unlikely to be exact replicas of those that preceded them, even if they look the same.

That is not to say they definitely wouldn’t still fulfill the ecological niche they once did, helping shape and potentially restore ecosystems – a key argument for bringing back the mammoth, passenger pigeon and others.

There is the possibility however that the species’ particular niche has already been filled by others in the decades, centuries or millennia since they disappeared. This results in the resurrected species falling in the category of ‘invasive’, despite having technically been there first.

Invasive species are among the greatest threats to ecosystems across the globe, and historically when humans have got involved, moving animals where they wouldn’t be, things haven’t gone well.

Given the perilous position of thousands of living species on all seven continents, many argue the money spent trying to resurrect extinct animals would be better spent protecting those at risk of joining them.

Nevertheless, we’re still not quite at Jurassic Park levels, and some scientists don’t believe de-extinction will ever be possible. 

But for now, here are just three more of the animals scientists are trying to literally bring back from the dead.

The dodo

The phrase ‘dead as a dodo’ sums up the species’ tragic and rapid demise. With no fear of humans after evolving on the lush paradise of Mauritius, the large, flightless was easily preyed upon by Dutch soldiers who arrived on the island around 1600. In addition, deforestation and destruction of their nests by other predators brought by settlers meant the dodo became extinct around 80 years after the Europeans’ arrival.

However, bringing birds back from the dead poses additional scientific complications due to the nature of avian reproduction. The de-extinction process at present requires access to an egg cell, or female gamete, that is ready for fertilisation. This is relatively simple to procure in mammals, less so in birds.

Instead, scientists at Colossal Biosciences, which is driving the project, are having to go a step further back. Eggs are formed from primordial germ cells, and it is these that scientists are attempting to manipulate using the dodo genome to one day reproduce the famous bird.

The quagga

The species that started it all is in fact not a species at all, but a subspecies – although this remains contested by some. Like the dodo, they were wiped out by European settlers, and the last quagga died at Amsterdam Zoo on August 12, 1883.

Efforts to revive this enigmatic equine, with its distinct half zebra, half horse colouring, have been ongoing in South Africa for almost 40 years at The Quagga Project. Working on the basis that the quagga is a subspecies of the plains zebra, a team of scientists has been using selective breeding of individuals to effectively try to concentrate the genes of those with the most quagga-like characteristics, eventually producing individuals that resemble the quagga and bears its distinctive coat pattern.

But will that be a quagga, or an unusual zebra?

Tasmanian tiger

Despite its name, the Tasmanian tiger is not a cat, and despite its looks, is not a dog. It is – or was – a carnivorous marsupial. 

Like the quagga, the last of this great species died in a zoo. In the case of the thylacine, or Tasmanian tiger, it was a particularly unfortunate end – staff had locked the animal out of its shelter and, two months after the species was granted protected status, it died from exposure on September 7, 1936.

And like the dodo, excessive hunting and habitat destruction by European settlers – plus the introduction of disease – led to the thylacine’s rapid extinction.

But now, Colossal Biosciences, the firm behind the dodo resurrection, is hoping to restore the thylacine, and aims to have a ‘de-extincted thylacine-ish thing’ within a decade.

The company is also working on bringing back the woolly mammoth – within the next five years.

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