Despite Biotech Efforts to Revive Species, Extinction Is Still Forever

A revolution in genomics has created tantalizing new possibilities for conservation. A century and a half after Gregor Mendel proposed a mysterious unit of heredity in his pea plants, scientists now possess the tools to manipulate the genomes of living organisms. Conservation biotechnologists have experimented with ways to assist threatened species — for example, adding genes to boost genetic diversity in black-footed ferrets or cloning DNA to produce pharmaceuticals once made from the blood of horseshoe crabs.

Promising as these techniques are, the holy grail for some conservation biotechnologists has been to bring an extinct animal back from the dead. With a complete map of the missing species’ genome, it is theoretically possible to rebuild it in a lab. But it is not easy. The genomes of many vertebrates are more than a billion base pairs long, making it almost impossible to recreate without errors. A more realistic method favored by the handful of labs working on de-extinction is to systematically edit the genome of an extinct animal’s closest living relative.

Grazelands Rewilding did a low-tech version of this using a combination of lab work and old-fashioned breeding. They mapped the genomes of seven breeds of wild cattle before using artificial insemination and repeated cross-breeding to create a cow with aurochs-like DNA. Today’s eighth-generation tauros shares well over 99 percent of its genes with aurochs. Experts say there are 810 tauros alive today; about 350 are in herds in areas managed for wildlife conservation in Europe, while the rest are in breeding and holding locations in the Netherlands. But they remain, Grazelands Rewilding insists, tauros and not aurochs.

On the other end of the de-extinction spectrum, the Texas company Colossal Biosciences rejects Grazelands Rewilding’s hesitation over terminology. In October, it announced a plan to de-extinct the ivory-billed woodpecker, a spectacular, red-crowned bird once native to southern U.S. pine forests. It is also working to bring back the woolly mammoth (extinct for 4,000 years), the Tasmanian tiger (extinct since 1936), and the dodo (extinct since the late 1600s). The company says mammoths would fight climate change by trampling and compressing the snow that insulates the ground from winter’s deepest cold, thus helping keep the Siberian permafrost intact. Tasmanian tigers would restore an apex predator to hollowed-out Australasian forests. And the dodo would have symbolic value, rendering obsolete the phrase “dead as a dodo.” Colossal Biosciences has garnered plenty of media attention and says it has over $225 million in venture capital funding.

De-extinction’s appeal is obvious. If you can restore a keystone species, you will improve ecosystem function and generate excitement about conservation. It also comes with the satisfying feeling of righting a past wrong. But skeptics are not convinced. They complain the technology could divert attention and funding from more urgent conservation work, create new vectors for pathogens, and make extinction seem less of a threat.

Boosters and detractors have spent a decade debating these issues. But now, a new perspective is gaining prominence among scientists. Clare Palmer, a professor of environmental philosophy at Texas A&M University, captures the point directly: “From what I’m seeing, you are not really de-extincting anything. You are creating something else.”

The challenges begin with accurately mapping the extinct species’ genome. DNA starts to break down as soon as an animal dies. Any genetic blueprint from a museum specimen or from tissues found in permafrost will always be fragmented. The chances of perfectly recreating it are slim. A second problem is that animals have DNA in both their cell nuclei and in the cytoplasm outside the nucleus. This other type of DNA, mitochondrial DNA, is inherited from the mother during gestation. De-extincted animals don’t have mothers of their own species.

Other factors compound the difficulties. The microbial makeup of the surrogate womb would differ from the past. An infant mammoth or thylacine would be raised without siblings and by parents of a different species. Thanks to climate change, temperatures would be warmer. A new set of microbes and invertebrates would crawl over its skin. The behaviors and social environments that shaped the original species would be absent. The de-extincted animal may have visual similarities to the missing creature, but it would be far from the same thing.

Ronald Goderie, the Dutch ecologist who led the mission to create the tauros, recognized early on that ecologically meaningful de-extinction was impossible. An international team of scientists published a sequence of an aurochs genome in 2015. But Goderie knew aurochs were not just a DNA code that can be copied into a cow. “The gene pool of millions of animals, the population-structure, the behavior and habitat were just as essential for a successful project,” he said. Species are dynamic living forms that evolve over time and across continents. They cannot be cut and pasted into an existing animal.

Goderie is not alone. Ben Novak is the lead scientist at the California-based nonprofit Revive & Restore, where he heads the project to de-extinct the passenger pigeon from his lab in North Carolina. Although Revive & Restore uses the word “de-extinction” on its website, Novak points out that, “in the absence of a perfectly cryopreserved genome, we cannot actually recreate an original extinct species, no matter how much the science advances.” There will always be genetic information missing.

Novak published a paper in the journal Genes in 2018 with his own definition of de-extinction. His vision is one of “replacement by proxy,” where a living organism is adapted to serve the ecological function of the extinct species. The pigeon that Revive & Restore plans to recreate would be a hybrid, with both passenger pigeon and band-tailed pigeon genes. “Technically, the term de-extinction does not seem to really fit,” says Novak. “But it’s the one that was coined.”

So, it turns out that de-extinction may be more about creating valuable approximations than creating Jurassic Parks. This tracks the thinking of the International Union for Conservation of Nature, which in 2014 created a task force to develop a set of guiding principles for de-extinction. Its final report suggests the term “is misleading.” The careful language they crafted describes the creation of “ecological replacements” or “proxies.”

Letting go of the word de-extinction, surrenders a bit of the Hollywood buzz and relinquishes the appeal of the idea of undoing extinction. But there are advantages to giving up such a provocative word. It is more scientifically accurate, most importantly. “Deception is perhaps too strong, but people are being told they are getting something they are not,” says Palmer, the environmental ethicist. When she talks about de-extinction in her classes, she puts the word in quotation marks.

It turns out that Colossal Biosciences also recognize that de-extinction means something different from what many assume. Beth Shapiro, the company’s lead scientist, admits “It isn’t possible right now to recreate something that is 100 percent identical in every way — genetically, physiologically, behaviorally — to a species that is gone.” What the company aims to do, Shapiro says, is “[bring] back the core traits of an extinct species with the goal to replace missing ecological interactions in ecosystems.”

And the company’s ambition goes further. Since any animal created today will have to deal with a changed environment and a host of new challenges, she says, the company views de-extinction as a technology that looks to the biodiversity of the past and adds innovations to help species adapt to current and future conditions. Animals could be adapted to cope with heat stress, for example, or to fend off new diseases that come with a warming climate.

Whatever the fate of the word de-extinction, Palmer thinks restoring species similar to those missing can be a worthy goal. “In some cases,” she says, “it seems like there is a need for a species that is no longer there.” Grazelands Rewilding believes the massive weight of the tauros, the shape of its jaw, and the complex social behaviors of the herds are all ecologically valuable. European landscapes evolved their native diversity in the presence of wild, two-thousand-pound bovines. Thylacine-like predators shaped the ecology of Tasmanian forests. Close matches to extinct animals can reestablish important relationships between grasses, insects, and herbivores; return missing human encounters with charismatic beasts; and help counter the ongoing erosion of biodiversity.

The biotechnology expertise that accumulates through the work of companies like Colossal and Revive & Restore may also be important. While working on woolly mammoths, Colossal is developing a vaccine that protects against a herpes virus fatal to young elephants. Its work on the dodo has led to a conservation strategy for the Mauritius pink pigeon centered on genetic editing to counter inbreeding. Revive & Restore is applying biotechnology to problems faced by corals, Przewalski’s horses, and narwhals.

On the Lika Plains in Croatia, the Côa Valley in Portugal, and in Romania’s Danube Delta, small herds of tauros are learning to live alongside wolves and brown bears. The herds help restore vegetation and spread native seed through their dung. The scene evokes a hint of the paleolithic past. After all, aurochs played this role for millennia. But, from an ecological point of view, the tauros are here both to restore the landscape and prepare the ecosystem for what lies ahead.

The complexity generated by ecosystem- engineers like the tauros creates stability in the face of change. And everyone in this debate knows ecological stability will be crucial in the decades ahead, whether somebody chooses to call them “de-extincted aurochs” or not.