1. The dodo
Extinct since the mid-to-late 1600s
No animal is more associated with the word “extinct” than the dear dodo bird. The Dr. Seuss-esque bird died out just 75 years after Dutch sailors landed at its home island of Mauritius, off the coast of Africa. People brought invasive species to the island which, combined with hunting, drove the animal to extinction.
Some scientists want to bring the dodo back in an effort of “de-extinction.” To do this, they could use methods similar to how scientists cloned Dolly the sheep in the 1990s. But cloning the sheep wasn’t easy, and with an extinct animal, it would be even harder.
2. The moa
Extinct since the 1400s
Nine species of huge moa birds once roamed New Zealand, looking a bit like modern emus. They went extinct 600 years ago, right around the time that the first humans arrived on the islands. Scientists are pretty sure humans hunted them to extinction. It’s possible that Dolly-like cloning could bring them back.
To make Dolly, scientists took a cell from a sheep and removed the nucleus from the cell (the nucleus contains nearly all of an animal’s DNA). Then, they took an egg from a different sheep, removed its nucleus, and put the other one in instead. Finally, the egg was put back in the surrogate mother, where it developed into Dolly.
3. The Pyrenean ibex (the first animal to be brought back)
Extinct since 2000
The Pyrenean ibex, a wild mountain goat and subspecies of the Spanish ibex, used to live in the Pyrenees Mountains that separate France from Spain. As with many of these species, it was hunted to extinction. The last Pyrenean ibex died in 2000. And then again in 2003. Wait, what?
The Pyrenean ibex was actually brought back from extinction — for 10 minutes. Using the Dolly cloning method, researchers implanted Pyrenean ibex DNA into a hybrid goat/Spanish ibex. She gave birth to a Pyrenean ibex, but the newborn only lived for a few minutes because her lungs were deformed. She was the only one of 57 eggs to actually make it to birth.
4. The great auk
Extinct since 1844
These penguin-like birds lived on and around islands in the North Atlantic. They were expert swimmers, but were awkward on land and thus vulnerable to humans, who — again — hunted them to extinction. The last great auk egg was crushed under the boot of a fisherman as he grabbed its mother and father, snatching the species from the planet.
So would we be able to clone great auk back into existence? Well, the cloning process has worked with animals like Dolly the sheep, dogs, and even twin monkeys just recently, but it is very rarely successful. Scientists interested in de-extinction are looking into other methods to resurrect extinct animals.
5. The aurochs
Extinct since 1627
Once a common subject of cave art, the giant and wild cow-like aurochs hasn’t roamed Europe in a few centuries. While a handful of aurochs were domesticated to make cows, the rest were hunted to extinction. Pictured below is actually a Heck cow, an example of the “back-breeding” attempt to remake the aurochs.
One method scientists are using to try and bring back animals from extinction is selective breeding. Since aurochs DNA lives on in its cattle descendants, a bit in this breed and another piece in that breed, some people are trying to remake an aurochs from these relatives. They are breeding the cows with aurochs qualities to make an animal resembling their ancestor.
6. The quagga
Extinct since 1883
The quagga looks like a zebra that lost half its stripes. They once lived in South Africa until they were hunted to extinction — is this story getting repetitive yet? However, DNA evidence suggests the quagga was actually a subspecies of the zebra, so a group of people in South Africa started selectively breeding zebra to get these unique stripes back.
While the Heck cattle don’t particularly look like aurochs, the animals from the Quagga Project look remarkably like the quagga of old. So did they bring the animal back from the dead? It’s hard to say if the new quaggas behave like their extinct lookalikes, so the animals have been given the name “Rau quagga.”
7. The huia
Extinct since the 1920s
The huia bird was sacred to the indigenous people of New Zealand, but they were known in science for how their beaks differed between the sexes. About 800 years ago, when the Maori first arrived in New Zealand, hunting and habitat destruction threatened the bird. But once Europeans came to the island, invasive species and hunting snuffed it out.
Scientists are researching another method to bring back extinct species: gene editing. The idea is to take the DNA of the extinct species’s relative and snip out the pieces that are different between the two. Then, the scientists will insert DNA pieces from the extinct animal into the relative’s DNA.
8. The passenger pigeon
Extinct since 1914
Once upon a time, passenger pigeons blacked-out North American skies with their numbers. In the mid-1800s there were possibly billions of them, but their numbers dwindled as the century turned until the last known pigeon died in a zoo in 1914. The pigeons were so abundant that people thought they could never be hunted to extinction.
The scientists at Revive & Restore chose the passenger pigeon as their de-extinction mascot. Their plan is to compare the passenger pigeon’s genome to the genome of its still-alive relative the band-tailed pigeon. Then, they will edit the band-tailed pigeon’s DNA to look more like the passenger pigeon’s.
9. Irish elk
Extinct since approximately 7,000 years ago
The Irish elk — neither solely Irish nor elk, mind you — was the largest deer ever. At its shoulder, it was seven feet tall and its antlers were 12 feet wide. They lived all across Europe until about 7,000 years ago when the last one died. Thousands of years later, in the 1800s, its bones were used to prove extinction is actually real.
When scientists talk about resurrecting an extinct animal through back breeding or gene editing, they don’t mean an exact copy of the animal will be alive again. With these methods, the resulting animal would be a hybrid of the extinct species and its living relative. It would have qualities of both species.
10. The Tasmanian tiger
Last seen alive in 1936; declared extinct in 1982
These marsupials once lived in Australia and the surrounding islands, but a drying climate and loss of vegetation pushed them off mainland Australia 3,000 years ago; the last few were hunted to extinction on the island of Tasmania. In 2017, scientists sequenced the Tasmanian tiger’s genome, meaning they discovered the string of “letters” that made up their DNA.
While the Tasmanian tiger’s intact DNA is a great step forward for de-extinction (it could hypothetically make a genetic duplicate of the extinct animal), DNA isn’t the only thing that shapes an individual. A resurrected Tasmanian tiger, or any other species, will never be raised by a true member of its species and thus never learn certain behaviors.
11. Elephant bird
Extinct since the 1600s
The elephant bird was the largest bird to ever exist (one weighed about 1,700 pounds!), but it was a victim of egg-stealing. Their eggs were massive and so past humans thought they made great meals and/or giant rum cups. But while their eggs were once their demise, they may now be their savior. Scientists extracted elephant bird DNA from their egg fossils.
While some researchers are already on the train to de-extinction, others are asking if we should really be trying this at all. Jurassic Park seems to warn that bringing species back for our own amusement is a bad idea, so how do these modern scientists justify their research?
12. Hawaiian O’o
Extinct since 1934
It’s not clear just how this bird went extinct, but it was partly caused by habitat destruction by humans. Plus, people brought invasive species to the islands and hunted the birds for their flashy feathers. Flamboyant feathers are often tools for attracting a mate as well as blending into the bird’s environment.
The main argument for de-extinction is its tantalizing possibility of restoring ecosystems to their pre-exploited glory. Before humans messed around in these ecosystems, they were well balanced. Every animal, plant, and microorganism had its own role to play, so the loss of a species indicates that the ecosystem isn’t as healthy as it once was.
13. The woolly mammoth
Extinct since 4,000 years ago
Climate change and humans drove the woolly mammoth to extinction and now humans want to bring mammoths back — to fight climate change. Wait what? That’s right, some scientists think woolly mammoths will save the Arctic from itself because beneath the Arctic’s permafrost is a ton of carbon (like, twice as much as in our atmosphere).
And since climate changes make permafrost not-so-perma, that carbon is about to be released into the atmosphere as a greenhouse gas. In theory, bringing mammoths back to the tundra would reduce the trees, increase the grass, and thus lessen the amount of heat being absorbed.
14. The Caribbean monk seal
Last seen alive in 1952; declared extinct in 2008
Caribbean monk seals once lived, as their name would suggest, in the Caribbean and Gulf of Mexico. They were hunted to extinction by Europeans. Their relatives the Hawaiian and Mediterranean monk seals are currently endangered, with only around 500 adults left of each species.
If scientists want to resurrect extinct species because they played a particular role in an ecosystem, then can we just use one of its living relatives to do the same? In some cases, yes. On the dodo’s old home island, they’ve done this with a tortoise. But the species aren’t always similar enough for this to work.
15. The Heath hen
Extinct since 1932
The once abundant subspecies of greater prairie-chicken, the heath hen, lived in New England but disappeared by 1932. Its population had plummeted to only 50 birds in 1908 and conservation efforts got that number up to 2,000. But then fire, severe winter, invasive species, and disease took the birds.
So why would anyone want to bring back the heath hen if the very similar greater prairie chicken still lives in the United States? Well, some people argue the heath hen played an important role in its ecosystem that the living prairie chickens can’t fill because they don’t thrive on islands, as the heath hen did.
16. Steller’s sea cow
Extinct since 1768
At three times the size of its relative the manatee, Steller’s sea cow was huge. And while manatees enjoy the tropical waters of Florida, this giant loved the cold waters of the Arctic and kelp forests in the Pacific. But just 27 years after being discovered by humans, the sea cows disappeared. It was either hunted to extinction or lost its food source because the keystone sea otters were overexploited.
Some think the sea cow disappeared after many, many sea otters were killed. Otters are a keystone species; without them, there’s almost no kelp for the sea cows to eat. Sea otters have since grown in numbers, bringing back the kelp, but other habitats of extinct animals have not bounced back. So where would these resurrected animals go?
17. Spix’s macaw
Extinct in the wild since 2000
This beautiful blue bird was the inspiration for the animated movie “Rio” which follows the adventures of Spix’s macaw Blu as he’s taken to Rio de Janeiro to mate with another Spix’s. The two then have to escape being smuggled. The movie mirrors the real Spix’s macaw story, but with a slightly more hopeful tone.
The Spix’s macaw is extinct in the wild, partially due to being trapped and traded, but also as a result of habitat loss. There are a few dozen in captivity with hopes to reintroduce them to the wild, but much of their home is gone. So does it really make sense to try and bring them back?
18. The Carolina parakeet
Extinct since 1920
The Carolina parakeet was the United States’ only native parrot, until its demise in the 19th century. It’s a little unclear exactly why the parakeet went extinct, but it probably resulted from deforestation, disease, competition with invasive honeybees, altercations with farmers, or some combination of the four.
Some modeling research has suggested that a few extinct birds, including the Carolina parakeet, would actually live in a larger area than used to if brought back. So this brings about a new fear that one of these undead species could become invasive. Imagine being born into an alien world that your genes have never learned to adapt to.
19. Cuban macaw
Extinct since 1864
The Cuban macaw looked similar to other macaws, save for the yellow splashed across the back of its neck. Deforestation, hunting, and the pet trade got the best of this species. It was quite common around 1800 but its numbers declined until the last one died in 1864 (the picture below is a rendering of the bird).
Another critique of de-extinction is that the millions of dollars it would take to bring a single species back to life would be better used in conserving still alive species. While plenty of efforts are currently being made to keep species from going extinct, it’s still not enough to save every single one.
20. The gastric brooding frog
Extinct since the 1980s
While some of these animals have very similar relatives still alive, the gastric brooding frog was truly unique. It laid its eggs, then ate them and incubated them in its stomach. When a baby gastric brooding frog said “I came from Mommy’s stomach,” it was actually an accurate statement. For six weeks, Mommy’s stomach was a womb and she didn’t eat anything. Then she vomited up her children.
Using the Dolly cloning techniques, scientists got a gastric brooding frog embryo to divide into hundreds of cells, which is the first step toward becoming a full tadpole. But the cells can’t seem to get past a crucial stage of development, so the frog has not been brought back yet.
21. Baiji dolphin
Extinct since 2006
This freshwater river dolphin lived in China for 20 million years before it died out in the early 2000s. While it was nicknamed the “goddess of the Yangtze,” it clearly wasn’t treated as such. The baiji river dolphin was killed in boat collisions and caught in fisheries as bycatch (meaning they were fishing for something else). Dams and pollution degraded its habitat.
So how close are we to truly resurrecting an extinct species? It depends on which method and how you define de-extinction. In the next five years or so, there may be pigeons with passenger pigeon DNA. But it will likely be a decade or several before a more convincing resurrection.
22. Ivory-billed woodpecker
Last confirmed sighting in the 1980s
The ivory-billed woodpecker is a bird of great contention. The last confirmed sighting of the bird (in the United States) was in 1944, but since then people have reported seeing the bird. Scientists and birders debate whether or not the species is extinct or not. The bird was (is?) remarkable for its size, as the largest woodpecker in the United States.
For a few species, the discovery of the animal in the wild is a form of de-extinction. These animals are called “Lazarus species” — an animal believed to be extinct until it found alive in the wild. The coelacanth fish is a prime example of this and it’s possible that the ivory-billed woodpecker will be, too.
23. Caspian tiger
“Extinct” since 1970
The Caspian tiger, a tiger subspecies, once roamed the riverlands west of China, in what’s now Tajikistan and Kazakhstan. It was purposefully killed off to make room for agriculture, the last one reportedly dying in 1970. However, as scientists studied the Caspian tiger’s DNA, they realized it actually isn’t different from another tiger subspecies: the Amur tiger (often called the Siberian tiger).
The two tigers lived in different environments but had no substantial differences in their DNA. So now researchers are hoping to reintroduce Amur tigers into the habitats once occupied by Caspian tigers. The goal is to do it by 2022, the next year of the tiger, but Amur tigers are endangered. However, many live in zoos that could be released in the wild.
24. Northern white rhino
Functionally extinct; also called the “living dead”
The northern white rhino, a subspecies of white rhino, isn’t even extinct yet — there are exactly two females left — but scientists are already talking about resurrecting it. Neither of the females are healthy enough to actually have a baby, but they do have eggs that scientists hope to extract.
The eggs, combined with frozen sperm or DNA from other frozen northern white rhino cells, could be put in a surrogate mother: a southern white rhino. But as easy as “extracting eggs” sounds, it’s actually quite difficult. Alternatively, scientists might be able to turn their skin cells into egg cells, which has been done successfully with mouse cells.
25. Black-footed ferret
Nearly went extinct
While the black-footed ferret never went extinct — it was a mere 18 animals away — much of the species’ genetic diversity did. The several hundred that live now are all as genetically similar as half-siblings, so they are susceptible to being wiped out by disease. While we’ve enjoyed them as pets for decades, this particular example was apparently too rare for Earth’s stage.
However, in frozen ferret DNA samples, there is genetic diversity that the population could really benefit from. So, using techniques similar to de-extinction, scientists want to bring back those dead ferrets and put their diversity back in the population. These unique little critters may once again live on thanks to modern genetic research.