The Top 10 Candidates for De-Extinction

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Can We Bring These Animals Back from Extinction?

passenger pigeon
The Passenger Pigeon (Wikimedia Commons).

is a controversial scientific program whereby we may be able to resurrect long-vanished species, either by manipulating chunks of their fossilized DNA or by "de-breeding" tame populations into a close approximation of their wild forebears. Whenever an argument about de-extinction takes place, you're almost certain to hear about one of the 10 following birds, mammals or amphibians, which went extinct recently enough to make their revival, and re-introduction into the wild, a distinct possibility twenty, ten or even five years from now.

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The Tasmanian Tiger

tasmanian tiger
The Tasmanian Tiger. John Gould

The Tasmanian Tiger--also known as the Thylacine--can be considered the standard-bearer of the de-extinction movement. As far back as 1999, the Australian Museum announced plans to clone this marsupial predator, a scheme that fell apart a few years later when researchers were unable to extract suitable DNA from preserved specimens. Another team of scientists then picked up the baton, announcing in 2008 that they had restored the functionality of a single Thylacine gene. Presumably, the Australian outback is expansive enough to harbor a respectable Tasmanian Tiger population, though naturalists will have to make allowances for the Thylacine's diet (Australian farmers will doubtless be very protective of their sheep).

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The Woolly Mammoth

woolly mammoth
The Woolly Mammoth. Heinrich Harder

Given the frequency with which individuals are found encased in permafrost, you'd think it would be a snap to recover the intact genome of a Woolly Mammoth and clone this huge elephant back into existence. Well, think again: viable Mammoth DNA has proved surprisingly elusive, and there's also the matter of finding a suitable host to carry an engineered embryo (the most likely candidate would be a female African elephant). Perhaps most important, the Woolly Mammoth is (by far) the largest terrestrial candidate for de-extinction; even a small herd would require a huge amount of territory, and might wind up knocking other plant-eaters right out of the food chain (that is, if the newly cloned Woolly Mammoths aren't illegally hunted for their pelts and tusks).

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The Passenger Pigeon

passenger pigeon
The Passenger Pigeon. Wikimedia Commons

In the 19th century, Passenger Pigeons were hunted by the millions--and enough specimens have been preserved to make it possible (at least according to some experts) to reconstitute this bird's entire genome. At that point, the reasoning goes, it will be possible to manipulate the genome of the Passenger Pigeon's closest living relative, the band-tailed pigeon, and coax band-tailed females into brooding Passenger Pigeon eggs. What happens next is anyone's guess: these Passenger Pigeon hatchlings will either flourish and go on to breed healthy flocks, or they'll quickly suffer and die from lack of parental care (after all, it's not as if band-tailed pigeon parents have any stake in the Passenger Pigeon's survival).

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The Quagga

The Quagga. Wikimedia Commons

The Quagga's potential route to de-extinction is different from that of most of the other animals on this list. The closest living relative of this recently extinct Equus species is the Plains Zebra of South Africa, from which it diverged about 200,000 years ago. Theoretically, it should be possible to selectively "breed back" a population of Plains Zebras into a creature that looks very much like the Quagga, though whether this would technically count as "de-extinction" is open for debate. (Scientists have also succeeded in recovering intact DNA sequences from preserved Quagga individuals, but the prospect of cloning a Quagga, or combining its genetic material with that of the Plains Zebra, remains unlikely.)

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The Saber-Tooth Tiger

saber-tooth tiger
The Saber-Tooth Tiger. Wikimedia Commons

Of all the animals on this list, Smilodon--aka the Saber-Tooth Tiger--may be the longest shot for de-extinction. On the plus side, the Saber-Tooth Tiger is certainly the "sexiest" candidate; imagine the bidding war among zoos and nature preserves for the honor (and profit) of hosting a roaring, pouncing, canine-wielding family of Smilodons. On the minus side, it's not at all clear if sufficient Smilodon DNA can be recovered to make de-extinction a technical possibility, and it's not as if the Saber-Tooth Tiger has any especially close living relatives. And then there's the matter of what a successful re-introduction of the Saber-Tooth Tiger would mean for the defenseless prey animals of the Serengeti, not to mention the already-endangered big cats with which Smilodon would be in direct competition.

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The Dodo Bird

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The Dodo Bird. Roelant Savery

Will we soon need to retire the old expression "As dead as a Dodo?" Considering the challenges involved in de-extincting the Dodo Bird, probably not. The problem isn't that this poster species for human depredation went extinct over 300 years ago; it's that the Dodo was restricted to the Indian Ocean island of Mauritius, and hasn't left any close living relatives. As far as naturalists can tell, the flightless, big-beaked, 50-pound Dodo evolved from a stray population of pigeons, and the only viable candidate to brood a clutch of genetically engineered Dodo eggs would be the Nicobar Pigeon of the South Pacific. True, the Nicobar is bigger than most pigeons, but even a well-fed female wouldn't be up to the task of hatching and feeding a baby Dodo.

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Steller's Sea Cow

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A Hydrodamalis skull. Wikimedia Commons

The pinniped equivalent of the Dodo Bird, Steller's Sea Cow (genus name Hydrodamalis) was a ten-ton manatee that was hunted to extinction in the Commander Islands about 300 years ago. (Apparently, the species had been in decline for thousands of years, and this last straggling population managed to persist off the eastern coast of Siberia.) If you were handicapping Hydrodamalis in a de-extinction horse race, the odds would be something like 100 to 1: even if scientists managed to recover sufficient amounts of this animal's DNA, there would still remain the issue of finding a suitable female host to gestate the genetically engineered fetus. Since modern dugongs and manatees are a fraction of the size of Hydrodamalis, this is a long shot, unless we first manage to genetically engineer a gigantic pinniped female!

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The Auroch

The Auroch. Charles Hamilton Smith

About 10,000 years ago, the prehistoric settlers of India and Eurasia domesticated the Auroch, making this shaggy, one-ton grass-muncher the ultimate ancestor of every cow alive today. For this reason, the Auroch's route to de-extinction is the same as that for the Quagga, as scientists "breed back" cattle herds in an attempt to recover the original Auroch genome. One living result of this program is the breed known as "Heck cattle," whose resemblance to the Auroch is a matter of debate (for example, the biggest Heck bulls are only two-thirds the size of their Auroch forebears). It may also be possible to recover intact sequences of Auroch DNA, in which case de-extinction could be accomplished by combining Auroch genes with those of modern cattle and having a largish cow gestate the resulting fetus.

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The Gastric-Brooding Frog

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The Gastric-Brooding Frog. Wikimedia Commons

Don't be surprised if the obscure Gastric-Brooding Frog--and not the better-known Dodo Bird or Saber-Tooth Tiger--is the first animal to be successfully de-extincted. Comprising two separate species, separated by a few hundred miles along the eastern coast of Australia, the Gastric-Brooding Frog was famous for its method of reproduction: the females swallowed their eggs, hatched the tadpoles in their stomachs, and vomited their brood out into the wild. Since the last Gastric-Brooding Frogs went extinct less than 100 years ago, there is ample genetic material available, and scientists have already successfully created (but not gestated) living embryos. Even better, if the Gastric-Brooding Frog manages to stage a comeback, these same techniques may help to rescue the earth's dwindling amphibian populations.

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The Carolina Parakeet

carolina parakeet
The Carolina Parakeet. Wiesbaden Museum

The Carolina Parakeet may well turn out to be a case study in the perils of de-extinction. The only parakeet native to the eastern U.S., Conuropsis carolinensis was hunted to extinction a hundred years ago, prized for its green plumage (which was used in women's hats); other individuals were kept as pets, and wound up perishing in captivity. If scientists manage to bring back the Carolina Parakeet, what's to prevent history from repeating itself, as unscrupulous collectors pay vast sums for caged individuals, and equally unscrupulous hunters supply the couture trade with Carolina Parakeet feathers? (Think this is a long shot? Well, plenty of endangered parakeets are illegally imported into the U.S. from South America, despite the best efforts of government watchdogs and environmental agencies.)