Gene editing

Extinction has a pretty clear definition: gone forever. Or does it?

New advances using gene editing tools such as CRISPR or targeted breeding is quickly leading researchers to think about bringing some species—the passenger pigeon, the Tasmanian tiger, and the woolly mammoth, for example—back from extinction. But these projects are controversial for a number of reasons. At the extreme end is the Jurassic Park argument; should we really reintroduce animals that evolved and subsequently became extinct centuries ago into a world completely alien to them?

Despite what the dinosaur movies portray, however, we still don’t have the technology to bring something back from scratch (even if we had the complete genome of an ancient species). “There are serious limits to how far we can take this technology today,” said Ben Novak, lead scientist at Revival and recoverya non-profit organization that uses biotechnology to resurrect extinct species and save endangered ones.

In other cases, biologists work with species that have simply been extirpated from certain locales—you see, the concept of extinction is not always as clear-cut as it might seem. I did bison disappeared when humans domesticated them into modern cows, for example, or did the creatures simply change?

Florida panthers, on the other hand, never completely disappeared; but to help the genetic diversity of the dangerously few big cats left in the state, wildlife managers introduced cougars from a separate population into Texas. Panther numbers have increased as a result, but the cats that live there are now genetically different from the original panther population.

Below, check out a few examples of species that researchers have tried to bring back from extinction.

1. Pyrenean ibex

(Credit: MAV_malaga/Shutterstock)

The Pyrenean ibex is probably the only extinct animal that has been successfully brought back to life – although it only lasted a few minutes. The last of the animals died in 2000, but three years later scientists used its frozen cells to clone a calf. Although the clone survives birth, it dies a few minutes later due to pulmonary defects, which gives the ibex subspecies the distinction of being twice extinct. (Novak, for the record, says this popular claim isn’t entirely true, because a female doesn’t constitute a species. “Technically, she was never revived,” he says.)

2. Passenger Pigeon and Heath Hen

(Credit: ChicagoPhotographer/Shutterstock)

Extermination of passenger pigeons and chickens are the two projects that Revive & Restore is actively working on. The passenger pigeon program launched in 2012 and includes learning how to use CRISPR to edit the genes of banded pigeons, a close living genetic cousin of passenger pigeons that died out in the early 20th century. The closest living relative of the hen, which went extinct in the 1930s, is the greater prairie chicken.

Unfortunately, because birds lay eggs, scientists cannot rely on in vitro fertilization with them in the same way as with mammals. Researchers have made progress in growing reproductive cells in petri dishes for domestic chickens, which may help us understand more. But Novak says the recipe for keeping chicken cells alive doesn’t work for the cells of these two wild birds. Of those species, hens may be a bit easier to eventually restore, Novak says, because they are genetically closer to their living cousins ​​than passenger pigeons are to theirs.

3. Woolly mammoth

(Credit: Aunt Spray/Shutterstock)

One problem with reviving extinct creatures is that scientists must first obtain a complete genome. Researchers have been actively collecting mammoth DNA from museum specimens — and have mapped more than 90 percent of its genome, Novak says. But most of the genetic material that organisms carry is so-called “junk DNA” that may not be completely necessary for the functioning or uniqueness of a species. The trick is to find which DNA matters.

While the Asian elephant is the woolly mammoth’s closest living relative, the company’s current plan beautiful involves using an artificial womb to give birth to a calf instead of using a surrogate mother elephant. Using a surrogate, he said, would be extremely complicated because of the elephant’s two-year gestation period. Novak adds that gene-editing technology is not yet ready to make it realistic to revive mammoths and other extinct species; CRISPR can edit only a few dozen mutations per generation, while the mammoth has about 1 million genes that differ from Asian elephants.

4. Tasmanian tiger

(Credit: Daniel Eskridge/Shutterstock)

Humans captured the last known wild Tasmanian tiger, or thylacine, in 1930. Now the University of Melbourne is lead a project to bring back the animal, one of Australia’s most famous extinct carnivores, and recently received big cash boost from Colossal. The project also involves editing genes – in this case from the tigers’ closest living relative, the numbat.

5. Bison

(Credit: RudiErnst/Shutterstock)

Instead of gene editing, the work of recreating the wild version of our own domesticated cows involves reversing centuries of work done by humans to achieve a steady supply of milk and T-bone steaks. This involves selectively breeding cows to return the species to some semblance of what their ancestors may have looked like. The Project Auerrind, part of Rewilding Europe, is currently working on the science behind this as well as learning more about natural grazing in Germany. “Since it started in 2013, the Auerrind project has established four breeding herds in Lorsch, Einhausen, Bielefeld and Schwarzach, with cattle grazing on more than 50 hectares of land,” stated on its website.

6. California condor

(Credit: Barbara Ash/Shutterstock)

North America’s largest land bird disappeared in the wild in the 1980s when zoos took the remaining birds into captivity. Before that, biologists had to learn how to breed these giant birds in captivity without potentially harming the few that remained. They experimented with captive breeding of Andean condors — close cousins ​​of the California species — until developing a system for raising chickens and releasing them into the wild.

Captive breeding programs for California condors followed, including at places such as the condor sanctuary in Big Sur, California, run by Ventana Wildlife Society. The society releases birds every year; according to one study, there were about 334 in the wild in 2021. But challenges remain due to lead poisoning from ammunition. Recently, Dolan has been on fire condor release facilities destroyed and killed several wild fowls and chickens which could not escape the flames.

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