An uncomfortable but often overlooked tension exists between preserving biodiversity and protecting wild animals. Marris argues for taking a hard look at how humans make decisions about the lives of wild animals, from keeping them in zoos and as pets (a la the Netflix phenomenon Tiger King) to captive breeding and invasive species eradication programs. In the process, she poses questions that she admits at times feel heretical, such as whether the cherished idea that biodiversity has intrinsic, or objective, value—the “most fundamental” of Soulé’s value propositions. This question matters because if biodiversity does, that makes a strong case for its preservation.

Along her philosophical journey to an answer, Marris examines the case of the California condor, Gymnogyps californianus, whose populations became decimated from ingesting lead shot scavenged from carcasses hunters left behind. In a controversial move in the 1980s, humans collected the fewer than 30 remaining condors from the wild, including the last free-flying bird, “Adult Condor 9.” Some environmentalists and bird experts opposed the move to captivity, fearing condors would lose both dignity and wildness. The recovery program involved establishing a highly managed breeding regimen, raising chicks with hand puppets, and delivering mild shocks to teach naïve birds to avoid collisions with power lines once released. Hailed as a success, the program boosted the number of condors living in the wild to roughly 270, as of 2020. Yet even the “wild” birds still rely heavily on humans.

After reflecting on the program’s trade-offs, Marris makes an open appraisal of the condors’ worth, both as individuals and a species:

“Adult Condor 9 had final [intrinsic] value as a sentient creature, as do all living birds. I feel confident there. Gymnogyps californianus is valuable as a species to humans, who find it majestic and inspiring and fascinating (and do not want to feel guilty and bad if it goes extinct). Humans also value the species as a unit of biodiversity. Were it to go extinct, biodiversity would be lessened by one species, and any further evolution of the lineage would be cut off.

The ecosystem in which the condor lives is also more valuable to humans when the condor is present, because it has more species and more interactions between species.

Some also think the ecosystem is more valuable with the condor in it because the condor was there in the past. And I think that valuing previous ecosystem states is fine as long as we all agree that this preference is inherently cultural, not scientific.”

Ultimately, Marris concludes that all of these reasons come back to human—that is, subjective—values for the species. Then, she shares with us her honest reckoning:

“Do I agree that “biotic diversity has intrinsic value”?

I don’t know.

Just writing that sentence frankly terrifies me. I want to go dunk my head in a snow-fed creek and wash away my doubts. But I can’t. In a way I cannot explain rationally, I think that the diversity of life and the complexity of ecosystems matter, even if there is no one around to care. I think that there’s something precious in what we call “nature,” in the flow of energy, in the will to survive, in the way a lupine leaf holds a perfect sphere of rain. But I cannot present overwhelming arguments that this is true. I can only passionately assert it.”

Conservationists often say that humans should restore a declining species when we are responsible for its demise, but figuring out how and when to do that ethically is less clear cut.

For instance, in the name of conservation, humans kill huge numbers of introduced animals every year to protect a few priority species. “Bloodshed for biodiversity,” Marris calls it. She found that Australia alone was responsible for exterminating more than 200,000 feral cats over a single year between 2015 and 2016. This scenario is particularly common on islands, where humans have brought resourceful creatures like rats and cats, who often easily overwhelm the uninitiated, and frequently unique, native fauna. The Galapagos Islands are no exception. There, in service of tortoise restoration, Karl Campbell and the nonprofit Island Conservation aim to rid Floreana, a 100-person island, of every single introduced rat that might snack on tortoise eggs and young. Their approach, Marris writes, is “a carpet-bombing of poisoned cereal pellets,” using a broad-scale poison that causes drawn-out death by internal bleeding. Grim, but effective.

Island Conservation expects to spend an estimated $26 million over 10 years on Floreana’s rat eradication. Marris mulls the grisly cost against the potential future:

“Here on Floreana, humans are trying to undo the damage they have caused, to repopulate the island with the species (or subspecies) that are missing. Their intentions are good. Maybe some of those involved are motivated by the idea that human influence must be cut out of ecosystems like a melanoma, but Campbell seems simply to act from an impulse to fight extinction, preserve the diversity of life. And if things go as planned, all the rats will die at once during the poisoning, and no one will have to kill any more in the future. The killing can stop. [Local farmer] Claudio Cruz won’t have to spend a fortune on poison to protect his yucca. Rats won’t die on the edges of his fields every year. Baby tortoises will hatch and grow old. Long after I’m dead, they could walk this island, taking their unhurried steps, nibbling opuntia cactus fruit. Maybe it would all be worth it.”

Poisoning rats to save tortoises is one thing, but what about conservation experiments that would change—and sometimes kill—the animals we are trying to save? In the Australian Outback, ecologist Katherine Moseby is helping spearhead just such an experiment to give threatened native marsupials a shot against the (very large) island nation’s feral cats. At the Arid Recovery Reserve, Moseby and her collaborators have set up sprawling fenced-in enclosures. In one, are furry bettongs and bilbies—the control group—that have never seen a cat, and in another enclosure are both of these rabbit-sized marsupials, plus maybe one or two feral cats. The idea is that exposing naïve marsupials to low levels of cat predation over time will provide enough evolutionary pressure for bilbies and bettongs to adapt to avoid these predators, but not so much pressure they all die. Perhaps the result is a more wary bilby, or a more agile bettong, any of which might help these unique creatures survive the persistent feral felines that Australians have little hope of eradicating. But the goal is ultimately to tweak these animals’ genomes and make cat-savviness a trait that bilbies and bettongs pass to their young.

“Is this kind of manipulation of a wild animal acceptable when extinction looms? Moseby feels the crisis demands action and intervention, “not sitting back and saying, ‘Let’s let everything eat each other and see what is left.’”

One advantage of Moseby’s approach is that if it does work, the animals will be able to look after themselves in the future and will no longer be “conservation reliant.” Even a massive predator eradication on the scale of Predator Free 2050 in New Zealand implies that humans must continue to guard against new introductions of the predators. Here, if it works, the bettongs and bilbies should be set, even if humans stop caring about biodiversity—or stop existing.

I’ve argued that “genetic integrity” is a false value, like other purist attitudes that seek to freeze life in one state. If beloved biodiversity is on the line and the real-world suffering of animals is minimized, the fact that the animals are changed shouldn’t by itself make this route unethical. In a scenario where the bettongs fill up their giant open-air cage with babies and polish off all the food, who’s to say dying by starvation would not be worse than dying by cat? But this project opens the doors to serious questions about changing the animals we seek to save. How far are we willing to go?”

From here, Marris dives into the possibility of more direct genomic changes to wild animals, including gene drives that could theoretically force a desired genetic trait—say infertility in rats—to become dominant in wild populations in a matter of generations. In weighing the technology, she raises an important consideration for all potential human meddling: humility.

“Are we changing other species for us or for them?” she writes. “Is this a situation where the species we are worried about will be able to adapt to new conditions on their own, coming up with their own solutions, or are extinctions clearly going to occur without intervention?”

As disheartening as the slow erosion of biodiversity and the rising tide of extinctions may be, Marris reminds us that humans and wild animals can, and do, have mutually respectful relationships with each other. A better future for life on this planet is possible, and by the end of Wild Souls, she uses her characteristic humor and elegant writing to chart a path forward for humanity broadly and each of us individually. She presents a sort of rubric for readers, instructions for being a good human to the non-human world. We can use it, as Marris does, to discern our own values and then, whatever our situation, go on to evaluate specific ethical dilemmas involving our non-human kin. For her own part, she writes,

“If I were to try to summarize my conclusions in an Aldo Leopold-style guideline, it would go something like this: A thing is right when it promotes the flourishing and autonomy of living things, their diversity, and the complexity of their interactions—but where we cannot promote all these things at the same time, we must make our choices with care and humility. It’s a bit longer than Leopold’s version, but a pithy axiom does not always make for a bulletproof ethical system.”

All excerpts from Wild Souls: Freedom and Flourishing in the Non-Human World, by Emma Marris. Copyright © 2021 by Emma Marris. Used by permission of Bloomsbury Publishing.