Death is still forever, but extinction may not be. A dead body can't be reanimated once it begins to rot, but the essence of a species -- its genome -- survives rot for centuries, even thousands of years. That DNA knows how to make living animals, once we figure out how to invite it to do so. At the leading edges of synthetic biology the invitation is now being crafted. For some extinct species, regenesis is becoming plausible.
"De-extinction" is the new word signaling a new capability at the intersection of molecular biology and conservation biology. For several years scientists have had the ability to reconstitute the genomes of many extinct species from their DNA in well preserved museum specimens and some fossils.
Now it is gradually becoming possible to take the pure data of a reconstituted genome and convert it into viable DNA, piggy-backing on the living DNA of the closest living relative of each extinct species. The passenger pigeon (extinct 1914) might return via its relative, the band-tailed pigeon. The penguin-like great auk (extinct 1852) may swim again in the north Atlantic thanks to the closely related razorbill. Even woolly mammoths (extinct about 2000 BCE) could use living Asian elephants as DNA proxies and surrogate parents.
For molecular biologists the uncertainty at this point is not whether it is possible to edit living genomes -- that has already been done for small sets of genes in micro-organisms. The question now is how soon it will become practical to edit whole arrays of vertebrate genes, and to know exactly which genes are the ones to edit. Since 2005 the tools and techniques of synthetic biology have been plummeting in cost and soaring in sophistication at a rate four times faster than Moore's Law. Complete de-extinction techniques are not here yet, but at labs like George Church's at Harvard and the Roslin Institute in Scotland, the technology is so close and accelerating so rapidly that major steps toward reversing extinction can be expected in this decade.
Accordingly, conservation biologists are beginning intense discussions about whether they really want extinct species back, and if so, which ones? A few days ago the subject went public at a forum called "TEDxDeExtinction," featuring 25 scientists at National Geographic's headquarters in Washington DC. That event grew out of a prior private meeting of 35 molecular biologists and conservationists, held last October, also at National Geographic. (I was a co-organizer of both events.) Next month in Cambridge, England, the New-York-based Wildlife Conservation Society is running a three-day meeting on "Synthetic Biology and Conservation," with de-extinction as one topic for discussion. Debate at the meetings reflects changes going on deep within the conservation movement.
Kent Redford, the organizer of next month's Cambridge meeting and long a leading theorist for the Wildlife Conservation Society, said something pivotal at the forum in Washington: "My chosen field of conservation started off with a conviction that it is a crisis discipline, and you can only get people's attention by pointing out what is wrong and the terrible things that we're doing to the natural world. I think that after 30 years of that, people have stopped listening to us. I think that the lesson should be that hope is the answer, and that hope will get people's attention. That's why I'm less concerned about the details of de-extinction than I am about the lesson of hope that it can convey."
While most conservationists I've heard so far indicate they are excited by the prospect of resurrecting extinct species, all of them are also voicing concerns. Will scarce resources for the all-important task of preventing extinctions and protecting wild lands be diverted to spectacular but extremely expensive de-extinction projects? Will the harsh warning "EXTINCTION IS FOREVER" become so diluted that it no longer conveys the urgency of protecting animals on the brink of extinction? Might the new capability even be an excuse for allowing some species to become extinct because "we can always bring them back later"? And suppose a long-absent animal does make it back to the wild. Could it become a problem -- an all-too-skilled invasive that disrupts everything? Or might it restore ecological functions that we would welcome back?
Some arguments favor reviving extinct "keystone species" -- ones that had a disproportionately large effect on their environment relative to their abundance. When the wolf, an apex predator, was returned to Yellowstone National Park in 1995, a rejuvenating "trophic cascade" was set in motion. The wolves chased elk out of the river valleys; aspens grew back along the rivers; that allowed beavers to return and build dams; and beaver ponds became hotbeds of biological diversity. Might the return of extinct great auks, passenger pigeons, or mammoths have similar effects?
Penguins abound in the Antarctic, but they never lived in the Arctic. Their ecological role was filled in the northern Atlantic ocean by a similar large, flightless bird, the great auk. (The word "penguin" itself is said to be derived from an old Celtic name for the great auk.) Vulnerable on the few islands where they bred in dense colonies, great auks were hunted to extinction for their meat, fat, and down. They were such prolific fishers along all the northern coasts from Canada to Greenland to Great Britain that their disappearance must have been ecologically consequential. What would be the impact of their return? (One attraction of the great auk as a de-extinction candidate is that if its reintroduction was eventually deemed harmful, the birds would be easy to remove from their island breeding grounds a second time.)
The keystone function of passenger pigeons was as "ecological engineers" -- animals that create or modify habitats for other species either structurally, as beavers do, or by moving nutrients around, as salmon do. Passenger pigeons did both. The pioneer conservation biologist Aldo Leopold described them as a "biological storm." They were once the most abundant bird in the world, ranging America's eastern deciduous forest from the Mississippi to the Atlantic. The dense flocks opened up square miles of forest to regrowth when the weight of their numbers broke branches, and the deluge of their droppings added nutrients to the soil. Their demise came because commercial hunters slaughtered the birds most efficiently just when deforestation of the eastern woodlands was at its maximum in the late 1800s. Since then the forest has grown back dramatically, ready perhaps for the return of the ancient ecological dance between the trees and the birds.
Woolly mammoths were one of the most effective ecological engineers of all time. They dominated the largest biome in the world -- the once species-rich grasslands of the far north. It has been called the "mammoth steppe" because they were the leading mega-herbivore, trampling the moss-suffocated tundra into grass, knocking down and browsing the species-poor boreal forest into grass, and recycling nutrients with their dung. In their absence, which was largely caused by early human hunters, the tundra and forest have taken over. The northlands of America and Eurasia are not only less biodiverse as a result, they may be exacerbating climate change. Whereas grasslands fix carbon, the tundra is thought to be releasing vast quantities of greenhouse gases as it thaws. The Russian geophysicist Sergey Zimov has made a strong argument for restoring the mammoth steppe as a climate mitigation strategy.
Conservation biologists, intent in recent years on restoring the health of whole ecosystems, have been focusing ever less on individual species and ever more on ecological function. In studying the prospect of reviving certain extinct species they get to do both.
I predict that the outcome of their deliberations will be, "Let's do it -- carefully, incrementally, hopefully." I predict further that after all manner of fits and starts in the science, and no end of distractions in the public discourse, the dance of the passenger pigeons with their forest and ours will at last resume, and by the end of the century woolly mammoths will again tend their young in northern snows.