Around ten years ago, Stewart Brand, the founder of the “Whole Earth Catalog,” and George Church, a Harvard geneticist, met in Boston. Brand had an interest in using genetic technology for conservation, and when Church said that he read and wrote DNA, Brand told me, “that got my attention.” Reading DNA had been done before, but writing DNA was something new. The two hit it off and have been collaborating on a project to resurrect the woolly mammoth, the giant Arctic elephant that went extinct ten thousand years ago. Church is a pioneer in genetic technology—he helped develop the CRISPR-Cas9 technology that a researcher in China recently used on the world’s first genetically edited newborns—and, in his lab, scientists are working on bringing the prehistoric pachyderm back from extinction. The process would involve adding certain mammoth genetic adaptations, like a long, dense pelt and layers of insulating fat, to the DNA of Asian elephants, which share more than ninety-nine per cent of their DNA with their extinct cousins. Church and Brand have a vision of herds of future mammoths grazing the steppes of the far north.

Church’s woolly mammoth research is just one of several de-extinction projects—there are about ten underway now—that aim to use genetics to restore lost species. In her book “The Re-Origin of Species,” the Swedish science journalist Torill Kornfeldt travels the world meeting the scientists and conservationists involved in this movement. In California, she talks with Ben Novak, a scientist obsessed with bringing back the passenger pigeon—a bird that once travelled in flocks that were so giant and dense, Novak tells her, that they “swept through the landscape, with the same effect as forest fires.” In upstate New York, a researcher is working toward restoring the American chestnut, which was decimated by blight in the late eighteen-hundreds. Until then, chestnuts were so prevalent in the eastern half of the United States that, when their white blossoms fell in the spring, the hillsides looked like they were covered in snow; in the fall, their sweet, starchy nuts served as a free, abundant harvest. At Australia’s Sea Simulator aquarium, resurrection scientists are working on coral, which faces an existential threat from the rapid warming and acidifying of ocean waters. These researchers want to help coral avoid extinction by “trying to nudge evolution,” imbuing them with traits that will allow them to survive the hotter oceans of the future.

Some of the projects Kornfeldt writes about are incredibly compelling, given that we are living through a mass-extinction event that threatens the stability of the world’s ecosystems. But de-extinction’s appeal also works on a much smaller scale: who wouldn’t want to restore the beautiful chestnut to its former, generous glory? It disappeared from the Eastern forests so recently that, in some places, intact root systems still push up new saplings that grow briefly before succumbing to the blight that still lives in other, unaffected trees. And Kornfeldt’s account of seeing one of the last living northern white rhinoceroses—an elderly female called Nola, lumbering around her zoo enclosure, rotund and majestic—frames de-extinction as not just an ecological service but a rescue mission for individual creatures. By the time the book went to press, Nola had died, but cells of some of the last of her kind live on in the Frozen Zoo, a San Diego facility where eggs, sperm, and embryos from thousands of threatened or extinct species are kept in cold storage. Those tiny cells contain a world of possibility and rebirth, held in limbo under a layer of liquid nitrogen.

Nola makes for a charismatic ambassador of de-extinction, but some of the other projects raise big questions, both ethical and practical. It’s hard to imagine how one might go about introducing herds of woolly mammoths in the near-future Arctic: If the mammoths make it into existence, will temperatures in the far north still be cold enough to sustain a habitat for them? And just whose land do these giant herd animals get to graze? Meanwhile, the passenger pigeons, which used to descend in flocks that left areas picked clean and covered in guano, sound less Garden of Eden than Biblical plague. Another Harvard researcher, Arkhat Abzhanov, is modifying chicken embryos to make them more like their dinosaur ancestors; he likens his research to “examining birds’ family tree by moving backwards along the branches.” Abzhanov doesn’t let the embryos hatch, and it’s not clear that their mix of genetic features would allow them to function if they did. Kornfeldt writes that “chicken-sized dinosaur pets might sell like hot cakes” and “be delightfully harmless”—but if such animals were to be brought into the world, what would they be? It’s impossible not to think of Frankenstein’s monster, in both the creature’s monstrosity and its suffering.

It’s this tension—even more than the specifics surrounding the revival of any one species—that carries Kornfeldt’s stories along: she constantly pursues the question of what all of this means for humanity’s relationship to nature. To bring species back—from extinction or from its brink—is a godlike power. Stewart Brand, ever bullish on human potential, has said, “We are as gods and have to get good at it.” He sees species revival as part of a tech-forward approach to environmentalism. “Biotech has an enormous amount to bring to conservation,” he told me. We already wipe species out on the regular, so if we’re going to have godlike power, why not wield it intentionally and responsibly?

Ben Minteer, a professor of environmental ethics and one of the few de-extinction critics featured in the book, points out the danger of humanity becoming “mesmerised by its own power.” He recommends an “earthly modesty”: instead of trying to engineer our way out of planetary ruin by further altering nature, we should scale back destruction instead. The debate calls to mind what Bill McKibben wrote, in 1989, in “The End of Nature”: “We have deprived nature of its independence, and that is fatal to its meaning. Nature’s independence is its meaning.” By changing the climate through carbon emissions, he wrote, humanity had infiltrated every part of the wilderness, leaving nothing untouched. The same idea applies here. Whatever any of these genetically resurrected species might be, they won’t be part of nature.

Reading the science of de-extinction can inspire a lot of hope—not necessarily about the species themselves, but for demonstrating how relatively fast an area of science can develop. (The first genetically engineered plant was created in the early eighties. The human genome was sequenced in 2003. In 2006, a technique was developed to turn specialized cells into stem cells.) There’s an element of serendipity to scientific discovery, but that kind of progress doesn’t happen by accident—it’s the result of the concentrated effort that happens when broad swaths of society decide to make something a priority. In the nineties, the Human Genome Project was the new moon landing, publicly funded with almost three billion dollars from the U.S. government, and running alongside parallel projects supported by private corporations and other governments. When the first sequencing was complete, Bill Clinton and Tony Blair announced it together at the White House, using language that was heraldic even for Clinton: “We are learning the language in which God created life. . . . With this profound new knowledge, humankind is on the verge of gaining immense, new power to heal.”