Last year, hiking in Morocco’s eastern Atlas Mountains, I found an ammonite, a fossil of those spiral-shape cephalopods that to many symbolize paleontology itself. The fossilization process had turned the animal into pyrite—fool’s gold. It’s about the size of a small button, and although its luster isn’t great, the specimen is still special to me. It comes from my absolute favorite mass-extinction event—yes, I have a favorite mass-extinction event—and holding it is like holding that extinction in my hand and touching the black process intrinsic to evolution.
Pyritization of fossils occurs under unique geochemical circumstances, in this case widespread oxygen deficiency in Earth’s oceans, which was one of the key drivers of the Late Devonian mass-extinction event—one of the “Big Five” mass extinctions, the worst there ever were. Extinction studies is a relatively young field, still filled with great debates over the contours of causation; mountain-building and massive volcanism may have played some role in the pulses of Late Devonian mass extinctions, but plants—in particular the world’s first trees—appear to essentially have played the lead. The evolution of vascular systems—proper stems, branches, and roots—allowed them to conquer land, in the process breaking up rock, creating and stabilizing the first soils. The nutrients from these rocks and soils washed into the oceans, forming algal blooms that created vast dead zones and sucked up carbon dioxide from the atmosphere, which may have produced a global cooling. Overall, some 70 to 80 percent of animal species died off.
I call the Late Devonian my favorite mass extinction primarily because it shows that humans are far from the only organism to remake the Earth. Before the Late Devonian mass extinction, life on land was still very limited. The green terrestrial world we know today, of trees and bushes and flowering plants and all that depends upon and supports them, would not have developed had it not been for this mass-extinction event.
Likewise, the Carnian pluvial episode, a smaller mass-extinction event that I’m also fond of and that occurred some 230 million years ago, was so pivotal that the scientists who study this episode describe it as “the dawn of the modern world.” For millions of years, an extremely dry climate had extended across the supercontinent of Pangaea, until an episode of massive volcanism made the planet hotter and much more humid. It rained for about a million years, perhaps in waves that matched the four eruptive peaks of the volcanism. This global wetting led to another profound disappearance of many species, particularly of herbivorous reptiles that had adapted to arid conditions. But on this newly wet planet, a dazzling diversification of more modern coral reefs, conifer trees, dinosaurs, crocodiles, insects, and mammals began. “The origin of modern systems was triggered by the crisis,” Michael Benton, a prominent researcher of this extinction and a professor at the University of Bristol, in England, told me.
Extinction is often cast as a destructive force, but in this light, it is also generative. Even in the face of extinction, existing body plans—think of higher taxonomic categories such as phylum, class, or order—rarely disappear entirely. Meanwhile, the environmental changes that drive extinction events also drive the emergence of new body plans, notes the paleontologist Norman MacLeod, a professor at Nanjing University, in China. Extinction also removes the advantages of ecological incumbents—who themselves took advantage of a previous episode of rapid diversification, in many cases after an extinction event—and opens up opportunities for other groups. As a result, extinction has increased the overall range of diversity in the biosphere over time, a phenomenon known as evolutionary stacking.
“All these factors underscore the creative role extinction has played in promoting biodiversity,” MacLeod told me. “If there had been no extinction over the course of Earth history, our planet would be home to a far less diverse array of species than it is.”
Other than the emergence of new species, extinction is likely the most common evolutionary process on Earth. It is as necessary a part of evolution as death is of life, making space for new species—even whole new ecosystems—to emerge. And this kind of creative destruction is happening constantly: More dramatic events such as the Late Devonian fade into thousands or millions of more everyday extinction events that have made the world as we know it today.
Extinction’s beneficent side puts us in an awkward, even discomforting position. The world, after all, is on the upslope of another significant extinction event. Climate change, habitat loss, pollution, and a slew of other environmental problems are radically transforming ecosystems and resulting in a loss of biodiversity unprecedented in the history of our species, according to the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES)—the global body of researchers aiming to do for our current crisis of extinction what the IPCC does for climate change. In Earth’s history of extinctions, this one is distinct from all those previous in that it’s clearly caused by us. In the pursuit of our own interests, humans are profoundly reordering every environment on the planet, and extinguishing multitudinous lineages of organisms—the assemblage of species we live alongside.
Where does this leave us? Extinction is a tragedy for the species affected, but if we are just the latest in a series of evolutionary pressures, should we then be indifferent?
The answer is the intuitive one: We absolutely need to be worried about what humans are doing to the planet. But we should be worried about the transformations we’re causing and all the destruction of ecosystem services that they entail not because extinction is inherently bad, but—first and foremost—because these transformations might well destroy us.
Traditional environmental thinking tends to rely on the ideal of preservation to condemn human-driven extinction: Our actions are upsetting a supposed balance of nature that would persist if not for us, so our responsibility is to uphold that balance, guarding or re-creating a version of nature that does not so obviously reveal our influence. “The ravages committed by man subvert the relations and destroy the balance which nature had established between her organized and her inorganic creations,” the diplomat George Perkins Marsh, perhaps America’s first environmentalist, wrote in his 1864 text, Man and Nature—foundational to the conservation movement. More than a century and a half later, this same conceit governs environmental thought. You can see it, for instance, in the way environmental groups and thinkers describe the initiative to reintroduce wolves to Yellowstone National Park: After human actions “ruined” the ecosystem, the wolves were able to “restore balance” by reducing the number of elk in the park. (Never mind that for at least eight years after the wolves were returned, humans still killed more elk in the park than they did.)
This continuously recurring notion of some harmonious stability ignores the reality of nature’s constant dynamic flux. In trying to preserve an imagined natural balance, many conservationists assume that the current way the world is organized, with its current assemblage of species, is the way that it must always be. Evolution itself disproves that assumption: It has no purpose or direction, and does not end once a given condition is achieved. And any attempt to restore that imagined world in balance has involved making judgments, implicit or explicit, about which species are most worth saving. Beyond the self-interest of maintaining ecosystem services that benefit us, humans can and do have good reasons for trying to save polar bears, pandas, whales, tigers, sea turtles, rhinoceroses, orangutans, penguins, and other charismatic species from disappearing, but those decisions rely on human moral preferences. We have also deliberately eradicated the virus that causes smallpox, and if you accept that as a triumph or protest that those are just microbes, then you accept that not all species have an equal right to existence: that whales and orangutans—and people—are more important than bacteria and viruses.
Acknowledging that no perfect version of Earth exists—that extinction is as normal as any other evolutionary process, that the evolutionary-selection pressures humans are putting on the planet are as natural as the ones plants created in the Late Devonian—frees us to cop to those value judgments. A large extinction event today would just be another episode of Benton’s ecosystem revolutions for life on Earth, but it’d be lousy for humans. By warming the Earth, we would have a hard time eliminating all life—even in the worst-case models, the planet is still cooler than in many past eras—but, as the late paleontologist Stephen Jay Gould put it, “we can surely eliminate our fragile selves.”
The Canadian climate scientist Katharine Hayhoe has made a similar argument: “There is no one perfect temperature for the Earth, but there is for us humans”—the stable, moderate conditions of the Holocene epoch. Similarly, there is no perfect sea level for the Earth, but there is one for us: If it rises too high, many of our biggest cities and much of our arable land will flood. As IPBES scientists warn us, the current biodiversity crisis has already reduced the rest of nature’s capacity to provide beneficial environmental processes such as protecting coasts, building fertile soils, pollinating crops, and filtering air and water. Global warming exceeding 1.5 to 2 degrees Celsius will likely make coral reefs extinct—affecting the more than 1 billion people who depend on them as fisheries as well as for protection from storms and erosion. Stockholm University earth scientists have tried to identify other planetary boundaries—of ocean acidity, flows of nitrogen and phosphorus, and levels of stratospheric ozone—that define a safe operating range for humans. What exactly those boundaries are is a matter of some contention, but the notion that there are some optimum conditions for human life on Earth is not.
In many ways, fidelity to the idea that humans upset nature’s balance holds us back from addressing the perils of extinction. The conservation biologist Mark Vellend worries, for instance, that counts of biological diversity disregard new species in novel, human-influenced ecosystems—where extant species occur in new combinations or abundances. He gives the example of New Zealand. Since humans arrived, some three-quarters of that country’s forest has been converted for their use, a sizable chunk of all endemic birds have gone extinct, and non-native species have multiplied. But in that same period, he says, the number of plant species has doubled, the number of bird species overall has stayed roughly the same, and dozens of land mammals have moved in where none had lived. So is New Zealand an example of a biodiversity crisis, or a biodiversity success?
Vellend and others stress that this doesn’t mean global biodiversity is doing fine. Rather, it indicates that the erroneous belief that evolution follows a particular direction may be skewing our assessment. And if we do want to maintain, more or less, the current global assemblage of species—the assemblage to which we humans are adapted—then scientists need to be able to measure it accurately.
This skepticism of human influence is also getting in the way of mitigating the problems we have caused, perhaps nowhere more clearly than in agriculture. The notion that humanity is upsetting a natural balance is foundational to the widespread environmental opposition to genetically modified organisms, for example. Environmental groups regularly compare creating GMOs to playing God, casting them as yet another instance of our hubris running up against what nature intended, and bound to result in a disaster of unintended ecological consequences. Much the same naturalistic fallacy underpins support for organic agriculture: a belief that swapping in “natural” pesticides and fertilizers for their synthetic counterparts will lead to better outcomes for the Earth.
Yet the equation is not that simple. Both synthetic and natural fertilizers have the potential to run off fields and enter waterways, causing vast low-oxygen dead zones like that in the Gulf of Mexico. Left on fields, both types of fertilizer emit nitrous oxide, a greenhouse gas with some 300 times the climate impact of carbon dioxide. By contrast, GMO crops are one of our great hopes in sharply reducing agricultural greenhouse-gas emissions, for at least two major reasons. First, modifying cereal crops to produce nitrogenase—an enzyme that would allow them to convert atmospheric nitrogen into a usable form—would dramatically lessen the need for natural-gas-intensive fertilizer production and the resulting methane emissions. Nitrogen-fixing cereals would also avoid the problem of nitrous oxide wafting up from fertilized fields. (Another approach would genetically modify bacteria so that they can perform this nitrogen fixation in the roots of cereals.) And second, GMO crops that help farmers produce the same amount of food on less land can slow or stop the transformation of some of the world’s most valuable habitat into farmland—a major cause of both climate change and biodiversity loss.
In Italy, for instance, farmers have been trialing Arborio rice that was altered using the CRISPR gene-editing technique to be resistant to rice-blast fungus, which is expected to spread more widely with global warming; if successful, this gene-edited crop will sharply reduce the need for fungicides. In June, environmental activists destroyed fields of these crops, as they have vandalized other plots of GM crops over the years, condemning them as unnatural.
Plenty of innovations that serve human needs have been destructive for the environments we inhabit. But rejecting these human creations such as GMOs on the grounds that they are unnatural is, if anything, counterproductive to the goal of preserving a planet that supports human life, and the rest of the life on Earth that humans care about. Adding a dose of humanism to environmentalism does not mean abandoning concern for climate change, biodiversity loss, or any of the other severe ecological challenges we face. We are pumping out greenhouse gasses at rates that are orders of magnitude greater than the mass volcanism that played such a key role in many past extinctions, and so will likely be radically reorganizing the assemblage of species and set of conditions to which we are adapted. We still know so very little about how those transformations will affect us. Until we know more, in MacLeod’s mind, “the best thing we can do is take as much land as possible out of development and set it aside,” he told me. If anything, this way of thinking strengthens the justification for national parks and other modes of wilderness preservation, even rewilding. Human flourishing requires these precautions.
Picking up that Late Devonian rock in Morocco, holding that pyritized ammonite in my hand, made concrete this grand evolutionary dialectic that stretches from deep time to today. Without the evolution of vascular plants, and the mass extinction that followed, we would not exist. If we were to go extinct, some other assemblage of life forms would certainly follow. The ecosystem revolution we are setting in motion is not an on/off switch for life, but a gateway to a parallel world, a sliding door that we do not want to pass through. To say that the planet needs saving may be a fallacy, but we do need to save the version of it that makes us possible.
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