Scientists and conservationists will continue to debate whether such a scenario could—or should—come to pass.

De-extinction, opponents assert, is a shiny and superficial distraction from the hard, painstaking work of habitat protection, genetic rescue, and other proven ecological methods that the scientific world should focus on.

The introduction of revived species into existing ecosystems, critics contend, might post new—and deadly—risks to extant plants and animals.

Resurrecting species and creating the conditions in which they can thrive, critics warn, is a more complicated undertaking than proponents let on.

It is a mistake to think that "designing and releasing facsimile species somehow makes up for, maybe even reverses, the ecological mistakes of the past," Ben Minteer, a professor of zoology at Arizona State University, wrote for the Center for Humans and Nature, a nonprofit think tank, in 2015.

Ensuring that resurrected species have the sufficient numbers and habitat to thrive will be a complicated and time-consuming project, proponents concede, but that only makes it more worthwhile and inspiring. "To me, one of the greatest attractions of bringing back extinct species is how long it will take," Brand wrote. "For a baby female woolly mammoth to grow up and have a daughter takes twenty years. Getting herds back to the subarctic, grazing the mammoth steppe back into existence, will be a century-scale project. Children growing up in such a century might have a view of the relation of humans with nature that is not tragic, for a change."

Humans have a moral obligation, proponents of de-extinction contend, to bring back species that they played a part in wiping out.

De-extinction efforts would be a landmark scientific achievement, advocates assert, that would reinvigorate conservationism by awesomely demonstrating how humans can contribute to, rather than take from and destroy, the natural world.

Critics also point out that an animal's role in an ecosystem is often largely a result of learned behaviors.

Another pressing question surrounding de-extinction is how scientists should select which creatures to resurrect.

habitat is a particularly pressing concern for any de-extinction effort. The Yangtze River Dolphin, which went extinct in 2006, for example, could not feasibly be brought back until the river is cleared of the pollution that contributed to the species' demise.

Other potential challenges include whether a resurrected animal would be able to adapt to changes in the environment that have occurred since its extinction, including alterations in climate and available food sources.

Wray explained in Rise of the Necrofauna, "the role it once played in its ecosystem—as a fertilizer, forest disturber, predator, and so on—vanishes along with it. This absence leaves a niche unfilled, which in turn affects a cascade of other life forms that a species is always connected to, from the tiniest of mites to the tallest of trees."

These achievements, while notable, proved expensive and time-consuming. Recent advances in genetic editing technology, however, have made such efforts easier. Specifically, CRISPR—an acronym for clustered regularly interspaced short palindromic repeats—are bacterial DNA sequences that scientists have been able to harness as a kind of molecular scissors that makes genetic editing much less cumbersome.

accentuating

trepidations

Another drawback of captive breeding is that it produces the same lack of genetic diversity that tends to proliferate among isolated populations like the Florida panther.

Conservationists have also attempted to help endangered species through captive breeding programs that allow threatened species to mate and grow in protected surroundings before they are released into the wild.

Computer simulations run by paleobiologist John Alroy have found that sporadic hunting by a relatively small group of humans could, over a few centuries, drive large slow-reproducing animals like mammoths and giant ground sloths into extinction.

Captive breeding has significant drawbacks, however, including the absence of natural social instruction.

A focal point of these efforts has been one of the most powerful drivers of extinction—habitat loss. "As humans and their activities have spread across the globe to extract resources, plant crops, and build cities and roads," O'Connor wrote, "thousands of species inhabit slivers of their previous ranges, surviving in isolated populations with few places to expand and faced with a loss of genetic fitness and an increased vulnerability to climatic shifts, disease, and natural disasters."

Another tactic by which conservationists have attempted to help endangered species and imbalanced ecosystems is relocation—introducing endangered species into new habitats.

These questions have become more pressing as advances in genetic editing technology have made resurrection science increasingly feasible.

The concentration of carbon dioxide in the Earth's atmosphere is higher than it has been any other time in the last 800,000 years, climate scientists estimate, and, as a result of the accumulation of these greenhouse gases, scientists predict the global temperature will gradually rise by 5.4 to 9 degrees Fahrenheit by 2100, with potentially catastrophic consequences for life on Earth.

This view, however, did not account for sudden cataclysmic environmental events or humanity's impact on the environment, as was evident during Darwin's own lifetime with the disappearance of the great auk, a large flightless bird prevalent on rocky islands along the coastlines of Canada and northern Europe.

More broadly, some conservationists warn that de-extinction will divert resources and attention from efforts to protect living animals while potentially making the threat to endangered species seem less vital.

the thylacine, a carnivorous marsupial last seen on the island of Tasmania in the 1930s; and the heath hen, a wild chicken once prevalent in New England that went extinct in the 1930s.

warn that, though the rapidity of environmental decline seems dire, resurrecting animals would mark a dangerous intensification of human intrusion in the natural

journalist Elizabeth Kolbert wrote in her book The Sixth Extinction in 2014. "But extinction rates among many other groups are approaching amphibian levels. It is estimated that one-third of all reef-building corals, a third of all freshwater mollusks, a third of sharks and rays, a quarter of all mammals, a fifth of all reptiles, and a sixth of all birds are headed toward oblivion."

"Faced with these emergencies, the urgency to do something to save these species seems like a good ethical argument for action," journalist M. R. O'Connor wrote in her book Resurrection Science in 2015.

Supporters argue that humans, who for most of their history have failed to serve as mindful custodians of the natural world, have a moral responsibility to right some of their wrongs through de-extinction.

If humans cannot coexist with living species, they ask, how will they provide sufficient habitat and protection for resurrected animals?

According to the International Union for Conservation of Nature, which works to protect wild habitats and endangered animals around the world, about 900 species have gone extinct in just the past 500 years.

According to the International Union for Conservation of Nature, which works to protect wild habitats and endangered animals around the world, about 900 species have gone extinct in just the past 500 years.

Humans have a moral obligation, proponents of de-extinction contend, to bring back species that they played a part in wiping out.

De-extinction efforts would be a landmark scientific achievement, advocates assert, that would reinvigorate conservationism by awesomely demonstrating how humans can contribute to, rather than take from and destroy, the natural world.

Another pressing question surrounding de-extinction is how scientists should select which creatures to resurrect.

Critics also point out that an animal's role in an ecosystem is often largely a result of learned behaviors.

Other potential challenges include whether a resurrected animal would be able to adapt to changes in the environment that have occurred since its extinction, including alterations in climate and available food sources.

A focal point of these efforts has been one of the most powerful drivers of extinction—habitat loss. "As humans and their activities have spread across the globe to extract resources, plant crops, and build cities and roads," O'Connor wrote, "thousands of species inhabit slivers of their previous ranges, surviving in isolated populations with few places to expand and faced with a loss of genetic fitness and an increased vulnerability to climatic shifts, disease, and natural disasters."

habitat is a particularly pressing concern for any de-extinction effort. The Yangtze River Dolphin, which went extinct in 2006, for example, could not feasibly be brought back until the river is cleared of the pollution that contributed to the species' demise.

accentuating

Wray explained in Rise of the Necrofauna, "the role it once played in its ecosystem—as a fertilizer, forest disturber, predator, and so on—vanishes along with it. This absence leaves a niche unfilled, which in turn affects a cascade of other life forms that a species is always connected to, from the tiniest of mites to the tallest of trees."

These achievements, while notable, proved expensive and time-consuming. Recent advances in genetic editing technology, however, have made such efforts easier. Specifically, CRISPR—an acronym for clustered regularly interspaced short palindromic repeats—are bacterial DNA sequences that scientists have been able to harness as a kind of molecular scissors that makes genetic editing much less cumbersome.

trepidations

Another drawback of captive breeding is that it produces the same lack of genetic diversity that tends to proliferate among isolated populations like the Florida panther.

Captive breeding has significant drawbacks, however, including the absence of natural social instruction.

Conservationists have also attempted to help endangered species through captive breeding programs that allow threatened species to mate and grow in protected surroundings before they are released into the wild.

Another tactic by which conservationists have attempted to help endangered species and imbalanced ecosystems is relocation—introducing endangered species into new habitats.

Computer simulations run by paleobiologist John Alroy have found that sporadic hunting by a relatively small group of humans could, over a few centuries, drive large slow-reproducing animals like mammoths and giant ground sloths into extinction.

The concentration of carbon dioxide in the Earth's atmosphere is higher than it has been any other time in the last 800,000 years, climate scientists estimate, and, as a result of the accumulation of these greenhouse gases, scientists predict the global temperature will gradually rise by 5.4 to 9 degrees Fahrenheit by 2100, with potentially catastrophic consequences for life on Earth.

This view, however, did not account for sudden cataclysmic environmental events or humanity's impact on the environment, as was evident during Darwin's own lifetime with the disappearance of the great auk, a large flightless bird prevalent on rocky islands along the coastlines of Canada and northern Europe.

These questions have become more pressing as advances in genetic editing technology have made resurrection science increasingly feasible.

the thylacine, a carnivorous marsupial last seen on the island of Tasmania in the 1930s; and the heath hen, a wild chicken once prevalent in New England that went extinct in the 1930s.

More broadly, some conservationists warn that de-extinction will divert resources and attention from efforts to protect living animals while potentially making the threat to endangered species seem less vital.

warn that, though the rapidity of environmental decline seems dire, resurrecting animals would mark a dangerous intensification of human intrusion in the natural

Supporters argue that humans, who for most of their history have failed to serve as mindful custodians of the natural world, have a moral responsibility to right some of their wrongs through de-extinction.

"Faced with these emergencies, the urgency to do something to save these species seems like a good ethical argument for action," journalist M. R. O'Connor wrote in her book Resurrection Science in 2015.

According to the International Union for Conservation of Nature, which works to protect wild habitats and endangered animals around the world, about 900 species have gone extinct in just the past 500 years.

If humans cannot coexist with living species, they ask, how will they provide sufficient habitat and protection for resurrected animals?

journalist Elizabeth Kolbert wrote in her book The Sixth Extinction in 2014. "But extinction rates among many other groups are approaching amphibian levels. It is estimated that one-third of all reef-building corals, a third of all freshwater mollusks, a third of sharks and rays, a quarter of all mammals, a fifth of all reptiles, and a sixth of all birds are headed toward oblivion."

According to the International Union for Conservation of Nature, which works to protect wild habitats and endangered animals around the world, about 900 species have gone extinct in just the past 500 years.

According to the International Union for Conservation of Nature, which works to protect wild habitats and endangered animals around the world, about 900 species have gone extinct in just the past 500 years.

These questions have become more pressing as advances in genetic editing technology have made resurrection science increasingly feasible.

the thylacine, a carnivorous marsupial last seen on the island of Tasmania in the 1930s; and the heath hen, a wild chicken once prevalent in New England that went extinct in the 1930s.

More broadly, some conservationists warn that de-extinction will divert resources and attention from efforts to protect living animals while potentially making the threat to endangered species seem less vital.

If humans cannot coexist with living species, they ask, how will they provide sufficient habitat and protection for resurrected animals?

"Faced with these emergencies, the urgency to do something to save these species seems like a good ethical argument for action," journalist M. R. O'Connor wrote in her book Resurrection Science in 2015.

warn that, though the rapidity of environmental decline seems dire, resurrecting animals would mark a dangerous intensification of human intrusion in the natural

Supporters argue that humans, who for most of their history have failed to serve as mindful custodians of the natural world, have a moral responsibility to right some of their wrongs through de-extinction.

journalist Elizabeth Kolbert wrote in her book The Sixth Extinction in 2014. "But extinction rates among many other groups are approaching amphibian levels. It is estimated that one-third of all reef-building corals, a third of all freshwater mollusks, a third of sharks and rays, a quarter of all mammals, a fifth of all reptiles, and a sixth of all birds are headed toward oblivion."