Karl Campbell is a craftsman bedeviled by bad tools. He’s a middle-aged, medium-size, muscular Australian with a five-day beard and an intense gaze who seems perpetually coiled, even angry, when at rest. He’s smiling and relaxed only when his body is in motion—preferably fixing something, building something, or killing something.

His craft—and his mission—is saving as many endangered species as he can, in what he reckons the most effective way. It’s a grueling job by which he creates life out of death, preventing the catastrophe of irreversible extinction with a tide of blood. He kills goats and rats and other human-­introduced animals that threaten rare island creatures, but his tools—traps, long-range rifles, and poisons—are brutal, deployable only on a small scale and wildly indiscriminate. To excise the rat, say, from an ecosystem requires a sledgehammer that falls on many species.

Ecology is complex, even on tiny islands, and things don’t always go according to plan. In 2012, for instance, Campbell, who works for an organization called Island Conservation, helped round up the 60 Galapagos hawks that lived on Pinzón Island, a steep volcanic nubbin in the Galapagos chain, so they wouldn’t eat the rats that Campbell was about to poison. But when the rare raptors were released back into the wild after a couple of weeks, they began dropping like flies. It turned out the poison was lurking in lava lizards—hawk prey.

Campbell is now preparing for an even riskier maneuver: using a fiercely potent poison for the complete obliteration of rats on a 70-square-mile Galapagos island called Floreana. The island was once home to a chocolate-brown bird with a perky tail called the Floreana mockingbird, but the rats eat its eggs and chicks, so the bird remains on only a couple of islets. Once the rats are gone, the mockingbird could be brought back to the place for which it was named. The rats’ destruction will be brought about by a carpet-­bombing of lethal pellets: Some 300 tons of poisoned cereal will be dumped from helicopters, enough to kill every rat on the island. The problem is that 150 people and their farm animals also live on Floreana.

On a cool and sunny Monday last August, Campbell and I hopped in a local farmer’s battered Toyota Land Cruiser and headed for the highlands of Floreana. Rats are no friends to farmers either, and Campbell pointed to some corn in Claudio Cruz’s fields that had been nibbled away by sharp rodent teeth. Cruz had stacked two bright-red shipping containers up on blocks—one a gift from Island Conservation, one he bought himself. They will be used to store uncontaminated animal feed when the poison comes, tentatively in 2020. Island Conservation will also build coops, sties, and stables for the island’s chickens, pigs, and horses. It will buy sentinel pigs that will live outside the sties and be slaughtered at intervals so their livers can be tested for poison. The other pigs won’t be able to emerge until the sentinel pigs’ livers are clear. This might take three years. Parents will have to keep close watch over small children lest they eat pellets off the ground. Scores of native animals—likely including finches and short-eared owls—will be captured and held in aviaries both on and off the island. Campbell expects it will take 10 years and $26 million to clear this small island of rats.

All this is why Campbell has begun pushing for research into a much more precise and effective tool—one you might not associate with nature-loving conservationists. Self-­perpetuating synthetic genetic machines called gene drives could someday alter not just one gene or one rat or even a population of rats but an entire species—of rats, mosquitoes, ticks, or any creature. And this biological technology promises to eliminate these destructive animals without shedding a drop of blood. So Campbell has spent the past few years dividing his time between old-fashioned killing and traveling the world to pitch the gene drive approach to ecologists, ethicists, and prospective donors. He’s not alone in his enthusiasm. Institutions from the US military’s research agency to the Gates Foundation to the government of New Zealand are looking to gene drives as possible solutions for big problems (malaria, Lyme disease, species extinction). But the methods also contain the threat of unleashing another problem: They could change species, populations, and ecosystems in unintended and unstoppable ways.

Karl Campbell is looking for a better method than poisons to eradicate island rats. Jake Stangel

When Linda Cayot, project coordinator for a Galapagos-based restoration program called Project Isabela, picked Campbell for an internship with the organization back in the late 1990s, she recalls that one of his virtues was a “certain macho army roughness.” Campbell had learned to shoot firearms and repair vehicles in the Australian Army Reserve. He’d spent a few weeks volunteering to catch and arrest antelope poachers in Malawi. He was well suited to the demands of the work on the islands: Once he slashed open his thumb and had a friend stitch it up in the field; another time he came back from a visit to a remote volcano with most of the skin on his feet peeling off. He didn’t bother to mention it.