I was on the ground, 50 feet away from an aurochs.
At least it looked like one. Eight generations of rearing had resurrected an animal reminiscent of the giant bovine that plunged from Earth’s biota in 1627. The charcoal-black animal had the forward-pointing horns of the long-horned aurochs. It had the same muscular shoulders and neck. The bull’s legs were long and athletic. It even had a yellow “eel stripe” running down its spine, a distinguishing feature of aurochs. As I pulled grass from a Dutch field on a gray March afternoon, I thought about the art on the cave walls of Chauvet. If de-examination is possible, I went to see it.
The expert crouching next to me, however, didn’t refer to it as an aurochs. Oscar Campana Cardenas, operations manager of the Dutch nonprofit Grazelands Rewilding, called it “Tauros.” Indeed, everyone who has worked with Cardenas has referred to it that way. This careful labeling of the creature before me seemed odd. The visual resemblance to aurochs was striking, the nostalgic longing undeniable. But the deliberate choice of words made one thing clear. Grazelands Rewilding doesn’t consider itself in the business of expansion. Extinction, it believes, is permanent.
“They don’t really disappoint anything,” says one environmental philosopher. “They create something else.”
A revolution in genomics has created tantalizing new possibilities for conservation. A century and a half after Gregor Mendel proposed a mysterious unit of inheritance in his pea plants, scientists now possess the tools to manipulate the genomes of living organisms. Conservation biotechnologists have experimented with ways to help endangered species—for example, adding genes to boost genetic diversity in black-footed ferrets or cloning DNA to produce pharmaceuticals once made from horseshoe crab blood.
As promising as these techniques are, the holy grail for some wildlife conservation biotechnologists has been bringing an extinct animal back from the dead. With a complete map of the missing species’ genome, it’s theoretically possible to recreate it in a lab. But it’s not easy. The genomes of many vertebrates are more than a billion base pairs long, making them nearly 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 species.
Grazelands Rewilding has conducted 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 crossbreeding 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 bred and kept in the Netherlands. But they remain, Grazelands Rewilding insists, Tauros and not Aurochs.
At the other end of the de-extinction spectrum, Texas-based Colossal Biosciences rejects Grazeland’s rewilding hesitancy over terminology. In October, it announced a plan to deforest the ivory-billed woodpecker, a spectacular, red-clawed bird once native to southern U.S. pine forests. It’s 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 17th century). The company says that mammoths would combat climate change by trampling and compressing the snow that insulates the ground from winter’s deepest cold, thus keeping Siberian permafrost intact. Tasmanian tigers would restore an apex predator to hollowed-out Australasian forests. And the dodo would have symbolic value, rendering the phrase “dead as a dodo” obsolete. The colossal Biosciences company has attracted a lot of attention and says it has raised over $225 million in venture capital funding.
The appeal of de-extinction is obvious. If you can restore a keystone species, you improve ecosystem function and generate excitement about conservation. It also comes with the satisfying feeling of righting a past wrong. But skeptics aren’t convinced. They complain that the technology will divert attention and funding from more urgent conservation work, create new vectors for pathogens, and make extinction less of a threat.
Species are dynamic living forms that evolve over time. They cannot be cut and pasted into an existing animal.
Boosters and critics have spent a decade debating these issues. But now a new perspective is gaining traction among scholars. Clare Palmer, a professor of environmental philosophy at Texas A&M University, captures the point succinctly: “From what I see, you’re not really borrowing anything. You’re creating something else.”
The challenges begin with accurately mapping the genome of extinct species. DNA begins to break down as soon as an animal dies. Any genetic blueprint from a museum specimen or tissue found in the permafrost will always be fragmented. The chances of recreating it perfectly are slim. A second problem is that animals have DNA both in their nuclei and in the cytoplasm outside the nucleus. This other type of DNA, mitochondrial DNA, is inherited from the mother during pregnancy. De-extinced animals do not have mothers of their own species.
Other factors compound the difficulties. The microbial composition of the surrogate womb would differ from the past. A child 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 across its skin. The behaviors and social environments that shaped the original species would be missing. The de-optimized animal might share visual similarities with the missing creature, but it would be anything but the same.
Ronald Goderie, the Dutch ecologist who led the mission to create the Tauros, realized early on that ecologically meaningful densification was impossible. An international team of scientists published a sequence of an aurochs genome in 2015. But Goderie knew that aurochs weren’t just a DNA code that could be copied into a cow. “The gene pool of millions of animals, the population structure, behavior, and habitat were equally important for a successful project,” he said. Species are dynamic living forms that evolve over time and across continents. They can’t be cut and pasted into an existing animal.
Goderie isn’t alone. Ben Novak is the principal investigator at the California-based nonprofit Revive & Restore, where he leads the project to expand the passenger pairs from his North Carolina lab. Although Revive & Restore uses the term “de-extinction” on its website, Novak points out that “in the absence of a perfectly cryopreserved genome, we can’t recreate original extinct species, no matter how much science pours out.” Genetic information will always be missing.
Novak published a paper in the journal Gene in 2018 with his own definition of extinction. His vision is one of “replacement by proxy,” in which a living organism is adapted to serve the ecological function of the extinct species. The pigeon that is replicated and restored would be a hybrid, with both passenger pigeon and band-tailed pigeon genes. “Technically, the term de-extinction doesn’t really seem to fit,” says Novak. “But it was the one that was coined.”
“At the moment it is not possible to recreate something that is 100 percent identical to a species that is gone,” says one scientist.
So it turns out that de-extinction is more about creating valuable approximations than Jurassic parks. This is 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. The final report suggests that the term is “misleading.” The carefully crafted language they crafted describes the creation of “ecological substitutes” or “proxies.”
The word “de-extinction” is a loosening of the Hollywood buzz, giving up some of the allure of the idea of extinction. But there are advantages to abandoning such a provocative word. Above all, it’s more scientifically accurate. “The deception may be too strong, but people are being told they’re getting something they’re not,” says Palmer, the environmental ethicist. When she talks about the statement in her classes, she puts the word in quotation marks.
It turns out that Colossal Biosciences also recognizes that de-extinction means something different than what many assume. Beth Shapiro, the company’s chief scientist, admits, “It’s not currently possible to recreate something that’s 100 percent identical in every way—genetically, physiologically, behaviorally—to a species that has disappeared.” What the company aims to do, Shapiro says, is “[bring] back the core traits of an extinct species with the goal of replacing missing ecological interactions in ecosystems.”
And the company’s ambition goes further. Because every animal created today faces a changing environment and a host of new challenges, the company views expansion as a technology that looks at past biodiversity and adds innovations to help species cope with future conditions. For example, the animals could be adapted to cope with heat or shed new diseases associated with a warming climate.
Whatever the fate of the term, Palmer believes that restoring species similar to those that are missing can be a worthy goal. “In some cases,” she says, “it seems as if a species that is no longer there is required.” Grazelands Rewilding believes that the massive weight of the taurus, the shape of its jaw, and the complex social behaviors of its herds are ecologically valuable. European landscapes developed their native diversity in the presence of wild, 2,000-pound cattle. Thylacine-like predators shaped the ecology of Tasmanian forests. Close matches to extinct animals can restore important relationships between grasses, insects, and herbivores, returning missing human encounters with charismatic animals, and helping to counteract the ongoing erosion of biodiversity.
The biotechnology expertise accumulated through the work of companies like Colossal and Revive & Restore can also be important. While working on woolly mammoths, Colossal is developing a vaccine that protects young elephants against a herpes virus. Its work on the dodo has led to a conservation strategy for the Mauritius Pink Pigeon, focusing on genetic editing to counteract inbreeding. Revive & Restore is applying biotechnology to problems facing corals, Przewalski’s horses, and narwhals.
On the Lika Plains in Croatia, the Côa Valley in Portugal, and Romania’s Danube Delta, small herds of tauros live alongside wolves and brown bears. The herds help restore vegetation and disperse native seeds through their dung. The scene evokes a hint of the Paleolithic past. After all, aurochs have played this role for millennia. From an ecological perspective, however, the tauros are both here to restore the landscape and prepare the ecosystem for what lies ahead.
The complexity generated by ecosystem engineers like Tauros creates stability in the face of change. And everyone in this debate knows that ecological stability will be crucial in the coming decades, whether anyone calls them “de-extinctional aurochs” or not.