It’s harder than you might think to make a dinosaur. In Jurassic Park they do it by extracting a full set of dinosaur DNA from a mosquito preserved in amber, and then cloning it. But DNA degrades over time, and to date none has been found in a prehistoric mosquito or a dinosaur fossil. The more realistic prospect is to take a live dinosaur you have lying around already: a bird. Modern birds are considered a surviving line of theropod dinosaurs, closely related to the T rex and velociraptor. (Just look at their feet: “theropod” means “beast-footed”.) By tinkering with how a bird embryo develops, you can silence some of its modern adaptations and let the older genetic instructions take over. Enterprising researchers have already made a chicken with a snout instead of a beak.

This obviously adds to the general merriment of the world, and will eventually kickstart a roaring trade in exotic quasi-Jurassic pets. But there are a surprising number of other projects that aim to bring back more recently vanished wild animals, from the woolly mammoth to the Pyrenean ibex. Advances in gene-editing technology promise to make “de‑extinction” a potentially viable enterprise, but what exactly is the point? To answer this question, the Swedish science journalist Torill Kornfeldt has travelled to meet the researchers involved for this excellent book, written with a deceptively light touch (in Fiona Graham’s translation), that raises a number of deep questions and paradoxes about our relationship with nature.

To some, a few deaths by wolf would be an acceptable price to pay for a more exciting environment

The last mammoth died only 4,000 years ago, which means that fragments of mammoth DNA can be recovered, and scientists have pieced together a complete picture of how the mammoth genome differs from that of the modern elephant. In Siberia, maverick mammoth-bone hunter Sergey Zimov wants to reintroduce mammoths to the landscape, while a US professor of genetics, George Church, is working on how to build them, by splicing mammoth sequences into elephant DNA. But why? Church is motivated by the simple joy of doing something new and perhaps even improving on evolution. (“We might be able to do even better than the mammoth did,” he says.) Zimov and his son, meanwhile, point out that grazing megafauna such as mammoths, because of the way they knock over trees in heat-absorbing forest and root up the insulating top layer of snow on the ground, can actually keep overall temperatures down in their environment, and so counteract global warming.

This would only work, of course, at scale: if millions of mammoths were roaming across the European continent, along with gigantic herds of aurochs (the wild forebears of modern cattle) and other ghosts from the past. Such a world is, indeed, what some people want to see, and here ideas of de‑extinction coincide with the wishes of the modern “rewilding” movement, which wants to transform developed-world ecosystems by reintroducing wild animals, including predators such as wolves.

Part of the motivation is simply aesthetic, and part derives from a kind of species guilt. Scientists disagree over whether it was in fact humans, rather than early climate change, that killed off mammoths, giant sloths and other megafauna, but reviving them, to some minds, would be a kind of symbolic expiation for all our other environmental depredations, returning us to a prelapsarian innocence in our relationships with other animals. Stewart Brand, the countercultural godfather of hi-tech ecology, tells Kornfeldt: “I want the cod in the ocean to be the size cod used to be, for example. People go to the national parks in Africa and look at savannah full of animals, masses of animals and different species. Europe used to be like that, North America used to be like that, even the Arctic had that wealth of fauna. That’s my goal.”

Facebook Twitter Pinterest An illustration of the extinct giant ground sloth. Photograph: Aunt_Spray/Getty Images/iStockphoto

On views like this, a few human deaths by mammoth or wolf, let alone rampaging dinosaur, would be an acceptable price to pay for a more exciting environment of what Brand calls “bioabundance”. (Sweden’s wild boars, descended from a few that escaped from parks in the 1980s, now cause “thousands of traffic accidents every year”.) And indeed another researcher, who is working on bringing back the passenger pigeon – millions-strong flocks of which would periodically devastate local flora in the US – sees its role precisely as an agent of creative destruction. (“A forest needs a forest fire now and again,” he says.) Such visions are clearly based on an ecological nostalgia, a desire to return things to how they used to be and have them stay the same, and thus arise projects such as that to kill off “invasive mice” on islands off the coast of New Zealand, which is nothing but a kind of ecological eugenics.

But other thinkers in the field have long noted that any ecosystem is itself a process, always in flux. As Kornfeldt asks: “Why should nature as it is now be of any greater value than the natural world of 10,000 years ago, or the species that will exist 10,000 years from now?” An excellent counterpoint to the kind of ecology that wants to turn back the planetary clock is the recent book Darwin Comes to Town, by the Dutch biologist Menno Schilthuizen, which evinces great joy and optimism in its survey of how accelerating evolution is driving animals of all kinds to find new ecological niches in our cities.

The terrifying phenomenon that is pushing species towards extinction Read more

A more pragmatic criticism of de-extinction is that it diverts resources from the attempt to save species that have not yet become extinct. But the two are not necessarily competitive: in the case of the northern white rhino, of which there are only two in the world, they may be complementary. Kornfeldt visits the splendidly named Frozen Zoo in San Diego, which since the 1970s has accumulated a collection of cells from nearly 1,000 species frozen in liquid nitrogen. By cloning cells from a dozen rhinos, the zoo’s director Oliver Ryder hopes to re-establish a sustainable population; or, as Kornfeldt nicely puts it: “Twelve test tubes could enable new baby rhinos to rumble about once more like miniature armoured vehicles.”

The Frozen Zoo also contains cells from species that have already died out: for example, the Hawaiian poo-uli, “a small grey bird with a black mask around its eyes”. While scientists debated whether to try to catch the remaining birds, their numbers dwindled. Eventually a male was caught but no breeding partner could be found, and he died in captivity in 2004. His cells were sent to Ryder. “It was around Christmas,” he tells Kornfeldt, “and I was sitting at the microscope examining the cells when it really hit me – a sharp, intense realisation that this species was gone now.”

There are no right or wrong answers in this area, but as Kornfeldt implies, the rhetoric of such debates still revolves around a few presumptive virtues that are rarely interrogated deeply. The aim of greater “biodiversity”, for instance, often cited by the de-extinction researchers she interviews, is never, in truth, an absolute goal. We could save millions of people a year if we eradicated the malaria-carrying mosquito – perhaps, as researchers are now trying to do, by replacing them with genetically sterile individuals – but that would be a decrease in biodiversity. The fungi threatening to kill off some of our best-loved tree species, also covered here, are themselves organisms, as much as the trees they attack. Inevitably, those discussing such ideas are always choosing one species over another, and judging one ecosystem as somehow more authentic than another – not that nature itself cares much either way, being the most brutal engine of extinction on the planet.

• The Re-Origin of Species is published by Scribe. To order a copy for £12.74 (RRP £14.99) go to guardianbookshop.com or call 0330 333 6846. Free UK p&p over £10, online orders only. Phone orders min p&p of £1.99.