Rethinking extinction | Aeon

Iberian Wolves are proliferating in the Sierra de la Culebra, Spain after an absence of a century. Photo by Steven Ruiter/NiS/Minden Pictures/Corbis

Rethinking extinction







The fossil record shows that biodiversity in the world has been increasing dramatically for 200 million years and is likely to continue. The two mass extinctions in that period (at 201 million and 66 million years ago) slowed the trend only temporarily. Genera are the next taxonomic level up from species and are easier to detect in fossils. The Phanerozoic is the 540-million-year period in which animal life has proliferated. Chart courtesy of Wikimedia.










It took years of high-powered rifles, hunting dogs, helicopters and ‘Judas goats’ to kill every single one of the 160,000 goats on the islands



Okay, great news for islands. What about the whole world that is facing climate change? That really does look like a mass extinction event in the making.

Anyone who doubts the reality of global warming need only talk to a few field biologists. Everyone doing field research is discovering how sensitive the organisms they study are to slight changes in average temperature, in the length of the growing season, in rainfall patterns. But just because organisms are sensitive to change doesn’t mean they are threatened by it. Any creature or plant facing a shifting environment has three choices: move, adapt or die.

Evolution is far more rapid and pervasive than most people realise. The activity of all organisms all the time is summarised in the title Relentless Evolution (2013) by John Thompson. As Chris Thomas, a conservation biologist at York University in the UK, told New Scientist last year: ‘It is only recently we have come to realise quite how much evolutionary change is going on.’ What we might be seeing in response to climate change, he suggested, ‘is starting to look very much like a global acceleration of evolutionary rates’.

A major engine of accelerated adaptation and evolution, it turns out, is hybridisation. ‘Speciation by hybridisation is likely to be a signature of the Anthropocene,’ wrote Thomas in Nature in 2013. He told New Scientist: ‘Genes are jumping around. Molecular genetics is finding that hybridisation between species is more common than previously suspected. Darwin talked about a tree of life, with species branching out and separating. But we are discovering it is more of a network, with genes moving between close branches as related species interbreed. This hybridisation quickly opens up evolutionary opportunities.’


Move, adapt or die. When organisms challenged by climate change respond by adapting, they evolve. When they move, they often encounter distant cousins and hybridise with them, sometimes evolving new species. When they die, they leave a niche open for other species to migrate or adapt into, and a warming climate tends to open the way for more species rather than fewer. In the same Nature essay, Thomas wrote: ‘Global-diversity gradients dictate that more warm-adapted species are available to colonise new areas than cold-adapted species retreating from those areas as the climate warms.’

Throughout 3.8 billion years of evolution on Earth, the inexorable trend has been toward an ever greater variety of species. With the past two mass extinction events there were soon many more species alive after each catastrophe than there were before it.

There is no reason to be sanguine about climate change. It is the most serious problem currently facing humanity and nature. It might lead to the loss of some species that we lament greatly, but it will also usher in new species, and unless there is extremely ‘abrupt’ climate change, net biodiversity is unlikely to decrease dramatically. Abrupt-change scenarios have been dropping out of the climate models lately, thanks to ever-improving data and growing knowledge about climate dynamics. My own prediction is that climate change will be deemed intolerable for humans long before it speeds up extinction rates, and even if radical steps have to be taken to head it off, they will be taken.

The danger that is clear and present remains what Briggs has called ‘the precarious state of thousands of populations that are the remnants of once widespread and productive species’. The emerging term for the phenomenon is ‘defaunation’. In their survey on wildlife losses, published in Science last year, Rudolfo Dirzo, a biologist at Stanford, and colleagues, reported that terrestrial vertebrates are showing a ‘25 per cent average decline in abundance’ and that ‘invertebrate patterns are equally dire: 67 per cent of monitored populations show 45 per cent mean abundance decline. Such animal declines will cascade onto ecosystem functioning.’

The worry about ‘ecosystem functioning’ reflects a growing emphasis among conservation professionals. As the new science of conservation biology came into its own in the 1980s and ’90s, focus shifted away from concern about the fate of individual species and toward the general health of whole ecosystems. How serious is the ‘trophic cascade’ that results from an apex predator being absent or scarce? (Restoring wolves to Yellowstone National Park after a century’s absence proved the power of that concept when a rich array of wholesome changes came with the wolves.) What happens when pollinating insects become so reduced by pesticides that a region’s flora suffer? How important are large animals for moving nutrients around with their dung? What about carrion removers (vultures), stream cleansers (amphibians) and creatures that disperse seeds by eating them or hoofed animals that help plant them by trampling the soil? What is the role of large grazing animals in maintaining a healthy mosaic of forest and grasslands?


The extinction vulnerability of a particular species might help to draw public attention to a damaged ecosystem, and in the US it could trigger protection mechanisms of the Endangered Species Act, but in most cases it is at best an indirect sign of what is going wrong. The most relevant fact about the current cod population off of New England is not its relationship to zero (extinction) but that it is just 3 per cent of its historic size and therefore probably way out of whack with its ecosystem.

Part of the problem is in the way we classify degrees of endangerment. The Red List categories read, in order: extinct; extinct in the wild; critically endangered; endangered; vulnerable (that goes for Atlantic cod); near-threatened; and least concern. ‘Least concern’ is strange language. What it means is ‘doing fine’. It applies to most of the 76,000 species researched by the IUCN, most of the 1.5 million species so far discovered, and most of the estimated 4 million or so species yet to be discovered. In the medical analogy, labelling a healthy species as ‘least concern’ is like labelling every healthy person ‘not dead yet’. It’s true, but what a way to think. (The IUCN is aware of the problem, and to its great credit is developing a ‘Green List’ that will report on species whose situation is improving. It will categorise according to degrees of hope, for a change, instead of relying solely on degrees of dread.)

Of the several million species yet to be discovered, there is a reasonable argument that many are very rare and thus extra-vulnerable to extinction, but the common statement that ‘Species are going extinct faster than we can discover them’ does not hold up to scrutiny. According to the paper in Science ‘Can We Name Earth’s Species Before They Go Extinct?’ (2013) by the marine ecologist Mark J Costello at the University of Auckland and colleagues, the rate of documenting new species was 17,500 a year over the past decade, rising above 18,000 a year since 2006. There are ever more professional taxonomists (currently about 47,000) doing the work, along with burgeoning crowds of amateur taxonomists newly enabled by the internet. With a realistic current extinction rate of less than 1 per cent of species per decade and a discovery rate of something like 3 per cent a decade, the authors conclude: ‘the rate of species description greatly outpaces extinction rates’.

Ideally, along with the naming will come detailed information on the ecological situation and prospects of each newly described species. The scrupulous research conducted by IUCN volunteers on each of its studied species develops excellent data on important matters such as decreasing population, decreasing range and range fragmentation, but little ecosystem context is given. Is the animal a keystone species essential to the welfare of many other species, the way sea otters are essential to the health of kelp forests and everything that depends on kelp? Is the animal an ecosystem engineer capable of shaping the whole environment the way beavers create ponds that provide a home for many other species and also impound water into deep aquifers?

Or might the threatened animal be just one of several subspecies that all perform approximately the same ecological function? In that case its extinction might be inconsequential. That was the reality when the Galapagos giant tortoise ‘Lonesome George’ died in June 2012 and was mourned worldwide. Dubbed ‘the rarest living creature’, he was (probably) the last of his subspecies. Ecologists shrugged. Taxonomists shrugged. There are 10 more subspecies of Galapagos tortoise. Their population has risen from about 3,000 in 1974 to more than 19,000 now, thanks to ridding their islands of all goats and most of the rats and protecting the tortoises from hunting. Pinta Island, where Lonesome George’s line evolved, is now occupied by other Galapagos tortoises that are doing fine, carrying on his old job of eating up the excess understory vegetation and helping restore the island to its former ecological health. (Tortoises are so good at that, it has become a standard practice. To help with ecosystem restoration, giant tortoises from the island of Aldabra, off the east coast of Africa, have been introduced to Madagascar, the Seychelles, Mauritius, Reunion, Rodrigues, and a park in Kauai.)

Such animal ‘translocations’ are a thrilling development in conservation. They are becoming increasingly common and successful, according to the survey in Science ‘Reversing Defaunation: Restoring Species in a Changing World’ (2014) by the zoologist Philip Seddon at the University of Otago in New Zealand and colleagues. Before 1992, there had been 124 conservation translocations of vertebrate species; by 2005 the number was up to 424. Among the 424 are some species once declared extinct in the wild, such as the California condor and the black-footed ferret, which have been successfully bred in captivity and reintroduced to their old ranges. Others, such as the wolves of Yellowstone and the beavers being re-established in Sweden and Scotland, are wild animals translocated from their current range to reoccupy lands they were extirpated from long ago. Yet others are in an important new category called ‘ecological replacement’. The Aldabra tortoises in Kauai are there to replace a long-extinct, flightless ‘tortoise-billed’ duck.

‘Recognition of ecological replacement as a valid conservation tool,’ Seddon noted, ‘represents a departure from the single-species focus that once characterised conservation translocations and conforms more closely to the current global conservation emphasis on restoring natural processes rather than addressing only extinction risk.’ He went on to welcome the prospect, enabled by recent breakthroughs in genomic technology, of some extinct species being brought back to life and returned to the wild. (That’s something I happen to be working on full-time these years.)

The biotech tools that might enable a few cases of de-extinction could also soon be deployed to help prevent extinction in some species that are trapped in genetic bottlenecks or are afflicted with non-native diseases such as chytrid fungus in amphibians or the avian malaria that is threatening the native birds of Hawai’i. In parallel with the arrival of ‘precision medicine’ for humans, where treatment can be specific to the genomes of individual patients (and even individual tumours), we might see the development of ‘precision conservation’ techniques based on minimalist tweaking of wildlife gene pools. Some conservation scientists refer to it as ‘facilitated adaptation’ and see it as a form of ‘applied evolutionary biology’.

An early success story stars a glorious tree – ‘the perfect tree’, according to its many fans in The American Chestnut Foundation. These trees once comprised one-fourth of the whole eastern deciduous forest before an invasive fungus from Asia killed billions of them and reduced the species to effective extinction early in the 20th century. William Powell and Charles Maynard at the State University of New York did an ingenious bit of genetic engineering to introduce a fungus-resistant gene from wheat, creating a blight-proof American chestnut that can begin to take up its former crucial role in the eastern forest, as soon as the US government okays it as a benign genetically modified organism.

How should we gauge the health of ecosystems? Biodiversity – the sheer number of species present – is one important measure, widely used. The return of American chestnuts will increase the biodiversity of the eastern forest by one species. But it will do much more. We might need to add another measure of ecosystem richness we could call ‘bioabundance’. Unlike oaks, which generate bitter-tasting acorns infrequently, chestnut trees rain down a deluge of sweet nuts every year, feeding no end of wild animals (and many a happy human). They make the forest more abundant.

‘on each sq km there lived one mammoth, five bison, eight horses, and 15 reindeer’

Bioabundance is the best argument for two of the de-extinction projects I’m involved with – passenger pigeons and woolly mammoths. Ben Novak, a young scientist at The Long Now Foundation, is leading the work to revive and restore the most iconic extinct species in the US, the passenger pigeon. His research on the ecology of the bird suggests that its old niche as a forest pigeon remains wide open, and the eastern forest it occupied has regrown to most of what it was before severe deforestation helped drive the bird extinct in the 19th century. Their return in quantity – there used to be billions – could bring back the forest stimulation their dense roosting once provided through opening up areas of closed-canopy forest and enriching the soil locally with quantities of dung. In A Sand County Almanac (1949), Aldo Leopold, the founder of conservation biology, described passenger pigeons as ‘a biological storm… Yearly the feathered tempest roared up, down, and across the continent, sucking up the laden fruits of forest and prairie, burning them in a travelling blast of life.’ The passenger pigeons were like fire – good for the woods. Unlike fire, also good to eat.

As for woolly mammoths, their return to the vastness of the North American and Eurasian subarctic and Arctic might help restore the ‘mammoth steppe’ grasslands and flowery forblands that once comprised the largest biome in the world and one of the richest. The Russian scientist Sergey Zimov, the creator in 1988 of the ‘Pleistocene Park’ experiment in northern Siberia, estimates that before humans killed off most of the megafauna of the far north, ‘on each square kilometre of pasture there lived one mammoth, five bison, eight horses, and 15 reindeer. Musk ox, elk, woolly rhinoceros, antelope, snow sheep, and moose were also present. Wolves, cave lions, and wolverines occupied the landscape as predators. In total, over 10 tons of animals lived on each square kilometre of pasture – hundreds of times higher than modern animal densities in the mossy northern landscape.’ That’s bioabundance.

Some conservation projects, such as protecting African elephants or reintroducing California condors, require heroic effort, but a surprising number do not. In many places, long-missing wild animals are translocating themselves. Thanks to pollution clean‑up in European rivers, salmon are back in the Rhine, the Seine and the Thames. All across Europe, abandoned farmlands are reforesting and linking up into impromptu wildlife corridors, even in the absence of large formally protected areas. Europeans are welcoming back adventurous wolves, lynx, brown bears, wolverines, and jackals – all important predators.

In ocean conservation the best news is the sudden and rapid increase in marine protected areas, extending from the 34,000-square-mile Pelagos Marine Sanctuary for Mediterranean Marine Mammals to the 409,000-square-mile Pacific Remote Islands Marine National Monument whose expansion was proclaimed by President Barack Obama last September. Such refuges not only let marine life recover, they generate a surplus that can keep nearby fisheries stocked indefinitely. There are now 6,500 such sites, adding up to 3.4 per cent of the total oceans area. The goal of the global Convention on Biological Diversity is to get that up to 10 per cent by 2020. Protected land areas, which were 4 per cent of total land in 1985, are now at 15.4 per cent and headed toward 17 per cent.

The trends are favourable. Conservation efforts often appear in the media like a series of defeats and retreats, but as soon as you look up from the crisis-of-the-month, you realise that, in aggregate, conservation is winning. The ecologist Stuart Pimm at Duke University in North Carolina claims that conservationists have already reduced the rate of extinction by 75 per cent. Getting the world’s extinction rate back down to normal is a reasonable goal for this century. Restoring full natural bioabundance in most of the world will take longer, however. It would mean bringing wildlife populations back up to the marvellous level of ecological richness that existed before human impact. That could be a two-century goal.

But a perception problem stands in the way.

Consider the language of these news headlines: ‘Fuelling Extinction: Obama Budget Is Killer For Endangered Species’ (Huffington Post, February 2015). ‘“Racing Extinction” Sounds Alarm On Ocean’s Endangered Creatures’ (NBC News, January 2015). ‘“Extinction Crisis”: 21,000 Of World’s Species At Risk Of Disappearing (Common Dreams, July 2013). ‘Australian Mammals On Brink Of “Extinction Calamity”’ (BBC, February 2015). ‘The Sixth Extinction Is Here – And It’s Our Fault (Re/code, July 2014). The headlines are not just inaccurate. As they accumulate, they frame our whole relationship with nature as one of unremitting tragedy. The core of tragedy is that it cannot be fixed, and that is a formula for hopelessness and inaction. Lazy romanticism about impending doom becomes the default view.


How does nature’s prodigious robustness actually work? We don’t know yet! Not in detail. For instance we’ve just begun to glimpse how microbes work, and how the ocean works. Ecology is not yet a predictive science, and conservation biology is still a young discipline. With every increment of improvement in scientific tools, data and theory, and every single project expanding the breadth of conservation practice, we learn more about nature’s genius, and we increase humanity’s ability to blend in with nature, to the everlasting benefit of both.

BiologyEcology and environmental sciencesEvolutionThe environment

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