Despite Advances In Breeding, Science Consensus Grows That "De-Extinction" Is Likely Impossible

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A herd of tauros, animals bred to resemble the long-extinct aurochs that once roamed Europe. Grazelands Rewilding

I was crouched on the ground, 50 feet from an aurochs.

At least it looked like one. Eight generations of back-breeding had resurrected an animal reminiscent of the giant bovine that crashed from Earth’s biota in 1627. The coal-black beast had the forward-facing horns of the long-extinct 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 the length of its spine, a distinguishing feature of aurochs. As I watched him pull grass from a Dutch field on a gray March afternoon, I thought about the art on the cave walls at Chauvet. If de-extinction is possible, I was looking at it. The expert squatted next to me, however, did not call it an aurochs. Oscar Campana Cardenas, operational director of the Dutch nonprofit Grazelands Rewilding, called it a “tauros.” In fact, everyone who worked with Cardenas referred to it that way. This careful labeling of the creature in front of me seemed odd. The visual resemblance to an aurochs was striking, the nostalgic yearning undeniable. But the deliberate word choice made one thing clear. Grazelands Rewilding does not consider itself to be in the business of de-extinction. Extinction, it believes, is forever.

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Left: A drawing of what an aurochs bull looked like. Right: A tauros bull. Adapted from Richmond et al.; Grazelands Rewilding

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.

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https://e360.yale.edu/features/de-extinction