Dark Extinction Has Scientists Worried. Here's What They're Doing About It
If — when? — the African elephant goes extinct in an estimated two decades, there will be mourning and memory and tribute. People will post photos of themselves at the circus as kids. They'll mimic the noises those long trunks made for their own children and grandchildren. Science fiction often features human attempts to counter the cultural brunt of such extinctions, imagining worlds with robotic approximations of pets and zoo cages filled with taxidermy. These fictions of species loss generally assume that even as species die out, they will be chronicled and remembered, and that people will know what they have lost.
Most species, however, will disappear without a record, much less a eulogy.
The looming big-ticket extinctions of elephants, rhinos and right whales are stark outliers in the story of species death on Earth. Modern estimates put the number of plant, animal and insect species on our planet at nearly 9 million (though it could be many more), with about 86% yet to be discovered. And while the mechanisms of natural selection have always caused some species to die off at a gradual pace, known as the background extinction rate, human-driven climate change has sent this rate skyrocketing.
The result is a phenomenon known as "anonymous extinction" — the demise of undiscovered species humans never even knew existed, let alone had a chance to save.
Anonymous extinction, or "dark extinction," is a clear and present threat as the deterioration of the natural world outpaces our ability to learn about it. It raises questions of how we might conserve species with limited information and showcases humanity's conflicting roles as both the self-stated stewards of the Earth and its destroyers.
"The thing that worries me is whether I'm making the best decisions about where to protect species," says Stuart Pimm, a leading conservation ecologist at Duke University and the founder and president of the nonprofit environmental group Saving Nature.
"How do you make decisions when you don't have the knowledge?"
Losing unknown species has been a long-time reality for biologists, but the phrase "anonymous extinction" has yet to gain widespread use. Now, with extinction rates estimated to be anywhere between 1,000 and 10,000 times the planet's background rate and growing, labeling anonymous extinctions offers a way to contextualize these additional losses, revealing patterns scientists might use to prevent them from occurring in the first place.
A growing concern
Though the term "anonymous extinction" didn't originate with him, many of its recorded uses can be traced to Paul Marek, a Virginia Tech entomologist who frequently surfaces the phrase when discussing millipede species he's discovered over the years.
"As someone who describes and discovers species and places them in the bigger evolutionary history of things, addressing and avoiding anonymous extinction is something that I very much get up thinking about in the morning," he explains.
The millipedes Marek studies are arthropods, members of a subgroup of invertebrates containing all insects, spiders and more. The unique challenges of discovering and describing these species (for one, they're puny) make them disproportionately vulnerable to anonymous extinction. Of roughly 1.2 million described species on Earth, Marek estimates about 1 million are arthropods. (Despite this, invertebrates are notoriously underrepresented in scientific research.)
With so many closely related species, it can be difficult to identify a new one by sight alone. Some of the defining characteristics of the millipede species that Marek has discovered, including the exact number of legs on the world's first true millipede, have required laboratory equipment to distinguish.
It's not just small, hard-to-distinguish species that are at risk of extinction before discovery. Geographical constraints can make larger species more vulnerable, too. For instance, research suggests that birds and mammals in island environments face extinction rates up to 187 times greater than those of continental counterparts.
Plant species are the most geographically vulnerable, since escaping a home changed by climate or destruction isn't an option. Ecuador's Centinela Ridge, located in the Andean cloud forest near the coast, was once known among botanists for its abundance of unknown plants. When the ridge was deforested to make way for farmland around 1990, dozens of unnamed species were believed to be lost. One of them, a small flowering herb of which four samples had already been collected, was later named Gasteranthus extinctus.
In 1992, the story of the Centinela Ridge popularized the term "centinelan extinction" to describe the loss of geographically constrained species resulting from the unnatural destruction of entire habitats. Miraculously, or perhaps through the sheer force of cosmic irony, G. extinctus has since revealed itself elsewhere in the region, but many other natives of the Centinela Ridge will not be so lucky.
The overlap between centinelan extinctions and anonymous extinctions is significant. A 2011 paper, co-authored by Pimm, used a statistical model to calculate that more than 70% of the estimated 60,000 undiscovered plant species may live in the world's 36 or so biodiversity hotspots. "These are places where at least 80% of the habitats are being destroyed," Pimm says. "They're being hammered hard." Understanding the biodiversity of these vulnerable areas can help researchers estimate which types of unknown species are being lost.
Geographic restrictions can be a driver of anonymous extinction, but they might also clue us in to missing species. Take the Brazilian millipede Pseudonannolene silvestri, a crawler that bears little resemblance to others in its home region. Its closest living relatives are a set of tortoiseshell striped millipedes in Alabama and Tennessee, the only ones of their kind in the entire United States. Millipede migration between Brazil and Alabama would take an enormous amount of time on little legs, explains Marek, long enough for a species to evolve many times over along the way. Populations of each millipede iteration should be sprinkled along the route like breadcrumbs. But none of these relatives who set up shop along the journey have been found, Marek says, which could indicate they've gone extinct.
The potential consequences of unchecked anonymous extinction go far beyond a loss of niche scientific knowledge. Many of Earth's ecosystems function like complicated and inscrutable machines. Within those machines, it's often rare species that perform the most critical functions — dispersing seeds, consuming harmful species, providing essential nutrition and much more. When a species is unknown, it's impossible to predict or plan for the ramifications of its loss on its environment.
Marek points out that combating anonymous extinction is also important for more human-centric reasons. Failing to support and sustain biodiversity could have real consequences for bioprospecting, the unearthing of species with unique biology that can inspire innovation in materials science or be used to create medicines and more. But unchecked for-profit species discovery isn't a great solution for the Earth either.
Insufficient regulations mean there's a fine line between helpful bioprospecting and unfair commodification of natural resources, which often exploits the traditional knowledge of Indigenous communities. And bioprospecting can also harm species themselves, even as they provide utility for humans — just ask the horseshoe crab, which was long harvested for its biomedically invaluable blood.
In some cases, describing a species can also mean dooming it. New species may gain attention from conservationists, but they can also become targets for wildlife traffickers and poachers.
A February study evaluating data on 53,808 vertebrate species described since 1758 found newly discovered species are significantly more likely to meet the requirements for threatened status than those we've known about longer, in part because of poaching. (Another key reason is that we tend to be discover new species with larger populations first.) What's more, the authors predicted the percent increase in known vertebrate extinction risk from 1758 to 2019 is likely to repeat again in just the next 30 years. These novel species are enticing prospects for wildlife traffickers because new means rare and rare means pricier.
In such circumstances, secrecy can sometimes be the best course of action. One recent discovery Pimm's team has made is the Dracula irmelina, an Andean orchid named for the mother of the Saving Nature celebrity benefactor Leonardo DiCaprio. Saving Nature's taxonomists have published all of the standard scientific information for the species, along with its region of discovery, but only a trusted colleague would get the coordinates out of Pimm.
"I have not told you exactly where it is," he says proudly. "And I have no intention of telling you exactly where it is."
When Marek has the opportunity to do fieldwork, in addition to hunting for millipedes, he keeps his eyes peeled for other interesting-looking arthropods that fall under some of his colleagues' specialties. "If we're in a very unusual location," he says, "and if we have permits for a greater diversity of things, we definitely collect more things, and deposit them in the Natural History Museum with the idea that 20 years down the road, folks might find that to be a new species."
An overwhelming number of undiscovered species currently sit on the shelves and in the basements of the world's natural history museums, where, some long past their anonymous extinctions, they patiently wait to be legitimized in the eyes of scientists. Estimates put the average length of time a species in a museum collection waits to be discovered at 21 years, but there's really no upper limit.
To Marek, this backlog represents the last, and possibly the greatest, remaining barrier in his quest to prevent anonymous extinction: There just aren't enough taxonomists, the scientists most equipped to describe and classify new species. The exact reasons for and severity of this dearth of faculty and funding has been debated long enough that the problem has earned a formal title: the "taxonomic impediment." Regardless of whether the problem lies in funding or in interest (the answer is that it's a bit of both), most scientists working on conservation and discovery agree the current taxonomic output is insufficient.
"We need more diverse taxonomists in places like Brazil, the Amazon, Equatorial Africa, Thailand. These are the places that have super-rich biodiversity at its most innocent and most in peril," Marek says.
In September, a group of international entomologists argued that scientists should rush to scoop up unknown species like they're filling a dried and jarred Noah's ark, building a preserved collection that will "testify to the vanishing biodiversity of our planet." Only after preserving these samples should the work of identification begin, they write, "even if the species have fallen to extinction in the interim."
It's an approach that effectively throws the towel in on conservation, and relies on the premise that scientific knowledge will retain inherent value in a world in which the opportunity to use it — primarily for protection — has passed.
For others, the question of discovery for discovery's sake is murkier. "As a systematist," says Marek, "that's what I do — I describe species. But my main goal is to preserve biodiversity. If we can preserve a species' habitat, I would feel comfortable not knowing it."
Many conservationists agree with Marek, which is why the last few decades have seen conservation efforts aimed solely at protecting single species become more balanced withs attempts to preserve entire ecosystems. It's a strategy that's supported by a growing body of research demonstrating the importance of biodiversity to the health of humans and the planet. A biodiversity-forward approach — one that focuses on keeping the proverbial ark afloat, rather than monitoring its passengers — could be the key to slowing down anonymous extinction.
In a world in which most species, known or unknown, are struggling, there's comfort in imagining a rare exception somewhere thriving, unnoticed and untouched by human hands.