Therefore, one may suggest that knowing the entire genetic code of some creature would automatically provide a recipe for making it. Unfortunately, things appear to be more complicated in the real world…

Vladimir Kremlev for RT. Click to enlarge

Since November 2008, when a joint team of American and Russian scientists published the near-complete DNA sequence of the extinct woolly mammoth in the Nature scientific journal, there has been a lot of speculation as to whether this astonishing creature, along with many others, could be brought back to life.

The New Scientist magazine went further, providing the potential “recipe” for reviving species from the dead.

The sad truth, though, is that creating a living creature from a virtual genome sequence is not possible right now…

However, the rapid progress in biotechnology gives hope, and the tempting idea of reviving some of those stunning beasts that once walked the Earth will certainly find its pioneers. After all, a few decades ago, cloning mammals or the possibility of sequencing entire genomes would have seemed science fiction.

T. Rex or Dodo – which one to pick?

Are we potentially capable of returning any of the extinct creatures from non-existence? And if not, what kind of criteria must be met in a candidate species to be selected for the hypothetical “Operation Phoenix”?

The primary condition would be the possibility to retrieve a complete genome sequence. To meet it, the creature would have to die recently enough, and in the circumstances in which DNA could be preserved.

Soon after death, DNA starts degrading, being attacked by various microorganisms and UV-radiation emitted by the sun. Yet in some conditions, such as at low temperatures of Siberian permafrost, or when a creature dies in a really dry region or dark cave, the DNA can last much longer. In this case, longer stretches of this molecule are more likely to be recovered.

Current estimates suggest though that even in the optimal environments there is an upper limit of maximum one million years through which a genetic material is likely to survive. So species that became extinct earlier – including all dinosaurs – are out.

“It's really only worth studying specimens that are less than 100,000 years old,” says Stephan Schuster, a molecular biologist at Pennsylvania State University, and a leading specialist behind the mammoth genome project.

The mammoth is not the only extinct species whose genome is almost fully sequenced, but also a few other similar projects are currently in progress. However, turning their results into living beings is uneasy task.

As Svante Pääbo of the Max Planck Institute for Evolutionary Anthropology in Germany has noted, “It's hard to say that something will never ever be possible, but it would require technologies so far removed from what we currently have that I cannot imagine how it would be done.”

Assuming that sooner or later we are going to have the necessary technology, New Scientist has proposed a list of several extinct creatures for resurrection, as well as critically endangered gorilla. Their choice is based on both the feasibility and each animal’s “megafaunal charisma”.

While it is still a big question whether gorillas are that close to extinction, with all the conservation programs and a large captive population, we believe there are much better candidates awaiting revival. Steller’s Sea Cow, no doubt, is among them. This giant sirenian was hunted to extinction as recently as 250 years ago.

Many others deserve restoration too – and let us hope they will appear on the real Phoenix List someday, and those mentioned below could be a good start.

Revival recipe

1. Well-preserved DNA. Its fragments would have to be extracted, sequenced and their sequences put together.

2. DNA synthesizers. Modern technologies do not allow synthesizing DNA molecules longer than a few thousand base pairs yet, with vertebrate genomes being billions of base pairs long. The DNA would also have to be synthesized in the correct number of chromosomes, having been typical of the extinct species.

3. Donor species. Next, the assembled genetic material would have to be injected into an egg taken from the suitable donor species. The original genetic material would have to be removed from the egg prior to the injection.

After that, the egg would have to be implanted into a surrogate mother, which would only be relatively easy in the case of mammals, while technology for egg-laying species, such as birds and reptiles, is still lacking.

“The Phoenix List”

Neanderthal (Homo neanderthalensis)

Drawing by Nikolay Kovalev (image from macroevolution.narod.ru)

The Neanderthal is an extinct member of the same genus that humans belong to. They lived in Europe and western parts of Asia. Our relative was heavily built and was probably exclusively carnivorous.

Extinct: approximately 25,000 years ago.
DNA: a draft genome sequence is expected to be published in 2009.
Potential egg donor, surrogate mother: Human.

Sabre-toothed tiger (Smilodon fatalis)

A large cat with extremely long upper canines, it once lived in North and South America and probably preyed on a wide range of large terrestrial mammals – from deer to bison.

Extinct: approximately 10,000 years ago.
DNA source: specimens from the La Brea tar pits, permafrost-preserved specimens.
Potential egg donor, surrogate mother: African lion.

Short-faced bear (Arctodus simus)

A third taller than the polar bear – the world’s largest living terrestrial carnivore – the short-faced bear was native to North America. This massive beast with a body mass around 900 kilograms (2000 pounds) could reach up to 50 kilometers per hour while running. There are conflicting opinions as to whether this species was an active predator or if it simply scavenged, using its impressive size to intimidate smaller predators from their kills.

Extinct: approximately 11,000 years ago.
DNA source: permafrost-preserved specimens.
Potential egg donor, surrogate mother: spectacled bear. Bear-cubs are born tiny regardless of the size of their mothers. So size difference between the two species should not be an obstacle.

Woolly rhinoceros (Coelodonta antiquitatis)

An adult animal was 3.7 meters (12 feet) in length and could reach extraordinary heights from 2.5 to 3.7 meters (8 to 12 feet) tall. Their fossils are not uncommon and have been discovered throughout Europe and Asia.

 Extinct: approximately 10,000 years ago.
DNA source: specimens preserved in permafrost.
Potential egg donor, surrogate mother: living rhino species. However, all are rare themselves.

Giant deer (Megaloceros giganteus)

Irish elk, or giant deer, was one of the largest deer species that has ever existed. Its geographic range covered a vast territory – from Western Europe through to East Siberia. A male stood more than two meters tall at the shoulder and sported antlers four meters wide.

Extinct: approximately 7,700 years ago.
DNA source: cave-preserved specimens.
Potential egg donor, surrogate mother: fallow deer.

Giant beaver (Castoroides ohioensis)

This massive inhabitant of prehistoric North America had a length of 2.5 meters (8.2 feet) and weighed up to 100 kilograms (220 pounds). Its teeth were broader than in the living species and grew to 15 centimeters (6 inches).

Extinct: approximately 10,000 years ago.
DNA source: remains in Eurasian Pleistocene peats.
Potential egg donor, surrogate mother: European or American beaver. Size difference would prevent the surrogate mother from carrying an embryo for the full term.

Steller’s Sea Cow (Hydrodamalis gigas)

image from www.itsnature.org

The story of this species is a shocking example of how destructive humans can be. These enormous toothless sirenians, reaching 8-10 meters in length (26-33 feet) and 8-10 tons in weight, were discovered in the Commander Islands in the North Pacific in 1741. Within the next 27 years these once numerous creatures were hunted to extinction.

 Extinct: 1768.
DNA source: alcohol-preserved skin sample.
Potential egg donor, surrogate mother: dugong. However, being much smaller than the sea cow, a surrogate mother would not be able to carry a fetus to full term.

Giant ground sloth (Megatherium americanum)

Once endemic to South America, the giant extinct relative of the living tree sloth species stood around six meters tall and could have weighed as much as four tons.

Extinct: approximately 8,000 years ago.
DNA source: specimens with hair, fossilized dung.
Potential egg donor, surrogate mother: three-toed sloth. The tiny relative might be able to provide eggs, but the fetus would quickly outgrow its surrogate mother.

Glyptodon (Doedicurus clavicaudatus)

This enormous mammal, the size of a small car, lived in South America and grazed on grass. It had a spiky, club-like tail, only increasing its resemblance of the dinosaurian ankylosaurs.

Extinct: approximately 11,000 years ago.
DNA source: well-preserved tissues are still to be found, preferably in a cool, dry cave.
Potential egg donor, surrogate mother: giant armadillo. Because of the size difference, it would only be able to carry an embryo for part of the term.

Tasmanian tiger (Thylacinus cynocephalus)

This species resembled a large, short-haired dog with a stiff tail and striped back. It was the largest extant carnivorous marsupial. The last individual, filmed on this footage, died in Hobart Zoo on the island of Tasmania in 1936. Having been extinct on the mainland Australia thousands of years ago, it survived in Tasmania, where hunting, diseases and introduced dogs undermined its populations and finally led to its full extinction.

Extinct: 1936.
DNA source: laboratory-preserved tissues.
Potential egg donor, surrogate mother: Tasmanian devil.

Dodo (Raphus cucullatus)

Dodo was a flightless pigeon that stood almost a meter tall, weighing about 20 kilograms (44 pounds). It was endemic to the Indian Ocean island of Mauritius. Its sad story is another glaring example of human destructiveness: the last bird died a little more than a century after the species’ discovery in 1581.

Extinct: around 1690.
DNA source: museum specimens yielded little result; searches continue.
Potential egg donor: pigeon.

Moa (Dinornis robustus)

This massive flightless bird stood around 3.7 meters tall (12 feet), and when Polynesians first arrived in New Zealand some nine centuries ago, they found forests full of these giant birds. The moas must have made easy meals, because a century later they were extinct.

Extinct: 500-800 years ago.
DNA source: well-preserved bones and eggs in caves.
Potential egg donor: no extant close relative, but engineering an embryo in an ostrich egg might work.

Many other obstacles, apart from those listed in the Revival Recipe, do not allow such a project to be launched right now, but with the rapid development of biotechnology, anything is possible.

Vitaliy Matveev, RT