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28 January 2022

Animals on the Verge of De-Extinction

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The quagga, a South African zebra with stripes on only the front half of its body, became extinct on 12 August 1883, when the last specimen died in the Amsterdam Zoo. A century later, in 1988, the quagga was brought back to life. According to an old environmentalist slogan, extinction is forever, but current advances are making the de-extinction of species a possibility increasingly within the reach of science.

However, the new quagga is not exactly the same animal as the old one. Thanks to the fact that 23 furs have been preserved in museums around the world, in 1984 the DNA of an extinct animal could be analysed for the first time. Analysis of the mitochondrial genome revealed that this equine was not a separate species, but a subspecies (Equus quagga quagga) of the common zebra (Equus quagga). A team of researchers from South Africa then had the idea that by selectively crossbreeding zebras it would be possible to restore the phenotype of the original subspecies.

Thus, in 1987, the Quagga Project was born, which the following year produced the first foal of what has been called Rau quaggas, in honour of the founder of the project, Reinhold Rau. Scientists cannot be sure that the result is a true quagga, since the genome of the subspecies is not known in detail. But with animals being born that are increasingly similar in appearance to the original quagga, researchers hope to someday repopulate the former domain of this African herbivore.

Interactive timeline: The Resurrection of Species

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The Quagga Project was the first attempt in the era of genetics to employ selective crossbreeding procedures to try to retrieve an extinct animal, but there have been previous attempts. In 1921, the German brothers and zoologists Heinz and Lutz Heck launched a breeding program to restore the auroch phenotype (Bos primigenius), the wild ancestor of modern cattle, which went extinct in the Jaktorów Forest in Poland in 1627. The two scientists, with the later support of the Nazi regime, created a new race called Heck, which is supposed to have traits similar to aurochs.

Selective crossbreeding is an application of the classical method of artificial selection explained by Charles Darwin in The Origin of Species and used by humans since ancient times to obtain new varieties of domestic animals. But it is the new bioengineering technologies developed in recent decades that scientists like Gwen Iacona, a biodiversity expert at the Center for Biodiversity Outcomes at Arizona State University, believe are now making the resurrection of species a reality: “The technical path is progressing very rapidly and some types of de-extinction are currently happening,” Iacona tells OpenMind.

Cloned animals

The first step on this path is cloning, a technique that in 1996 gave us the sheep Dolly, the first mammal cloned using DNA from an adult cell. In 2003, a team of Spanish and French researchers managed for the first time to obtain a clone from an extinct animal, the bucardo (Capra pyrenaica pyrenaica), the Pyrenean subspecies of the Iberian ibex, which went extinct in 2000. Cloning was possible because frozen cells from the last specimen had been preserved, but the kid was born with a defect in the lungs and died within a few minutes of being born.

Cloning requires intact DNA from the extinct species, which at the time dashed hopes of recreating animals such as the Tasmanian thylacine. The current aim of several groups of researchers is therefore to use cells from the closest living species and modify their genes to obtain DNA as close as possible to that of the extinct animal.

La bióloga alemana Angelika Schnieke fue parte del equipo responsable de la clonación de la oveja Dolly. Imagen: University of Edinburgh
German biologist Angelika Schnieke was part of the team responsible for cloning Dolly the Sheep. Image: University of Edinburgh

This genetic engineering is being applied to the recovery of the passenger pigeon (Ectopistes migratorius), extinguished in 1914 by massive hunting, and of which it was said that its immense flocks obscured the North American sky. The Great Passenger Pigeon Comeback project began in 2012 with the aim of editing the DNA of the band-tailed pigeon (Patagioenas fasciata), the closest living relative, and recreate the extinct bird.

The passenger pigeon project is the work of Revive & Restore, an initiative that also pursues the de-extinction of other species like the heath hen (Tympanuchus cupido cupido), which went extinct in 1932. But undoubtedly, the idea that has most caught the attention of the media and the public is the possible resurrection of one of the most iconic animals of prehistory—the woolly mammoth.

With support from Revive & Restore, the team led by geneticist George Church at Harvard University (USA) set out to introduce mammoth genes, identified from animals preserved in ice, into the genome of its closest current relative, the Asian elephant. The team has already succeeded with some genes related to small ears, fur and cold hardiness. In 2021, Church and tech entrepreneur Ben Lamm founded Colossal, a species de-extinction start-up that has taken over the mammoth project from Revive & Restore.

De-extinction projects have received a fresh boost in recent years thanks to the development of CRISPR technology, the molecular gene-editing tool that has made it possible to modify DNA with much greater ease and precision than more traditional systems. The launch of Colossal is based on the fact that Church is one of the pioneers of this technology, which he used to introduce the first mammoth genes into the elephant genome. CRISPR has also revitalised other de-extinction projects: Revive & Restore aims to obtain transgenic pigeons that carry the gene for Cas9, the enzyme responsible for cutting DNA with the CRISPR system. The complete sequencing of the thylacine genome in 2017 from samples preserved in alcohol has rekindled interest in its de-extinction, the first project of which was abandoned in 2005. However, there are serious doubts about whether any of these promises will materialise, as de-extinction projects have often been overly optimistic in their timelines.

Should we bring extinct species back to life?

The technical challenge is not the only obstacle to overcome on the road to de-extinction. Experts like Iacona not only wonder if we can bring some extinct species back to life, but whether we should: “There is discussion about the ethical and ecological implications,” she says. The main concern of Iacona is that this commitment dilutes the need to conserve the biodiversity that we still have today. “It does have the very real potential to distract us from the more effective and efficient ways of dealing with imminent conservation problems.”

But another danger of resuscitating extinct species, especially long-lost ones, is their environmental impact. “I would love to see mammoths too,” evolutionary biologist and environmental scientist Alexandre Robert of the National Museum of Natural History in Paris tells OpenMind. But a species is much more than just a species, he adds: “Even if you are able to reconstruct a mammoth, you will not necessarily be able to recreate a population that will persist, grow, adapt and play a functional role in its ecosystem.”

Mammoth reconstruction in The Royal British Columbia Museum in Canada. Credit: Rob Pongsajapan

The problem, Robert explains, is that the habitat of the woolly giant no longer exists. “The world where mammoths used to roam has been replaced by another world we call the Anthropocene.” Church’s project involves releasing the mammoths into the Pleistocene Park, a Siberian tundra reserve where Russian scientists aim to recreate their former habitat. But on this planet modified for the convenience of humans, it does not seem simple to find a place for these animals without causing irreversible ecological damage. “At present, it is impossible to know what will happen if we decide to bring them back to life,” concludes Robert. But what is clear to experts is what we should not do: rescue animals from extinction to lock them up in zoos. “It would be unethical to relegate a species to perpetual captivity,” says Iacona.

Javier Yanes


Editor’s note: Original text of October 2018 updated by the author

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