Is man on course to cause the sixth extinction?

Forthcoming book examines the role of humans in the eradication of species, and its findings are not likely to be pleasant
Robin McKie, The Observer The Guardian 8 Nov 09;

At first sight it seems an unlikely topic for a landmark publishing deal: a fee of about half a million dollars for a book about dead animals – or, to be more precise, extinct animals.

Nevertheless the subject of eradicated species has become publishing hot property after a bidding battle in the US saw Henry Holt, a publisher, beat its rivals to buy The Sixth Extinction by Elizabeth Kolbert last week. According to the New York Times, a "mid-six-figure advance" has now been agreed between writer and publisher.

"The idea of mass extinctions as the next step after talking about the perils of global warming is the most crucial subject," said Gillian Blake of Holt, after completing the deal with Kolbert, a writer for the New Yorker on environmental issues. Her last book, Field Notes from a Catastrophe, outlined evidence collated from sites across the planet showing how global warming is changing the world. The book was well reviewed on both sides of the Atlantic, with the Observer praising it as "a superbly crafted, diligently compressed vision of a world spiralling towards destruction".

Now, Kolbert is to focus on humanity's impact on the animal world, and in particular will look at the species that are today being rendered extinct by men and women. Scientists say the number of species being lost is approaching levels reached during five pivotal extinction events that have swept the planet over the past 600 million years. Among these catastrophes was the event that wiped out the dinosaurs 65 million years ago. Kolbert's task will to be show whether or not humanity – with its spiralling population, widespread habitat destruction, over-fishing and global warming – is rivalling these.

The theme is intriguing but not new. Nor is the title. In 1996 the distinguished palaeontologist Richard Leakey, with journalist Roger Lewin, produced his version of The Sixth Extinction, in which he argued that the five previous mass extinction events were now being matched by a sixth. "Homo sapiens is poised to become the greatest catastrophic agent since a giant asteroid collided with the Earth 65 million years ago, wiping out half the world's species in a geological instant," he says.

Other distinguished scientists, including EO Wilson and Norman Myers, have also produced works on this theme. None received advances like the one agreed between Holt and Kolbert, however. So what has changed? Why have extinctions become the subject of such attention and finance?

Answers have much to do with timing. Over the past decade, there has been a revolution in concerns about the environment – on both sides of the Atlantic. A succession of reports from United Nations wildlife experts and climate scientists have shown that our planet is in peril and that thousands of species are now hovering on the brink of extinction. For a decade, the public has been deluged with stories about the vulnerability of the tiger, coral reefs, amphibians and a host of other creatures. Hence the interest in Kolbert's new book.

In publishing terms, the move is also a significant one because it represents a shift from big-money outlays on works of fiction which have dominated the market in recent years. Huge sums, for example, have been paid to novelists such as Audrey Niffenegger for works – such as her latest, Her Fearful Symmetry – that have had disappointing sales. A dose of eco-horror might prove rewarding, it is thought.

Certainly, extinctions make a riveting and disconcerting subject. As Professor Norman MacLeod, keeper of palaeontology at the Natural History Museum in London, told the Observer: "We now know that 99.9% of all lifeforms that have ever existed on Earth have gone extinct. That means, to a first order approximation, that all life is extinct."

Obviously this latter, rather disturbing, scenario has not quite arrived. Nevertheless it does indicate that the constant eradication of lifeforms has been the norm throughout the history of life on Earth. It is the fate of all species to become extinct, a notion that should concentrate the minds of Kolbert's readers. The question is: what forces are responsible for the loss of vast numbers of species in such a short period?

Answers depend on individual cases, it transpires. For example, a huge asteroid crashing on Earth 65 million years ago is generally thought to have done for the dinosaurs. The vast plume thrown up by the impact coated the planet in dust and triggered a devastating climate change. As a result, 47% of marine genera (groups of related species) and 18% of land vertebrate families, including the dinosaurs, were wiped out.

And as evidence geologists point to the Chicxulub crater near the Yucatán peninsula, beneath the Gulf of Mexico, as the impact point of the asteroid.

Similarly the Triassic extinction, which occurred between 199 million and 214 million years ago, was most likely caused by massive floods of lava erupting from the Atlantic Ocean. These created a wave of global warming. In this case, around 22% of marine families and 52% of marine genera were eradicated.

Then there was the Permian-Triassic extinction, about 250 million years ago, which has been linked to both asteroid impacts and volcanism. This was Earth's worst mass extinction, killing 95% of all species, including an estimated 70% of land species such as plants, insects and vertebrate animals. Before that, the Late Devonian extinction, about 360 million years ago, killed 57% of marine genera. Its cause remains unknown. And finally, there was the Ordovician-Silurian extinction, about 440 million years ago, which has been linked with changes in sea levels and which led to the eradication of 60% of marine genera.

Life on Earth has, on some occasions, become remarkably unpleasant in a short space of time, to say the least – though this has not always been the prevailing view among scientists. In fact, Darwin thought extinction was a slow, painful business. "The complete extinction of the species of a group is generally a slower process than their production," he once remarked, a view that held sway for more than a century. Indeed it was only in the latter half of the 20th century that scientists uncovered evidence – the Chicxulub crater – that an asteroid crash must have been involved in the demise of dinosaurs. Extinctions could be sudden, they realised.

However, MacLeod urged caution in interpreting such discoveries. "Most palaeontologists dislike the idea that any single cause was responsible for one of the main extinctions," he said.

"Life is very robust and it takes a sequence of events to produce large-scale extinctions."

Thus the dinosaurs were wiped out at a time of considerable volcanic activity on Earth. Plumes of material were already sweeping the planet, plunging it into a period of global cooling. The crashing asteroid then administered a planetary coup de grace.

On top of volcanoes and errant astronomical objects, other factors involved in these mass extinctions include extreme ice ages which coated the planet in ice from pole to equator, and eruptions of deep-sea methane deposits that set off massive global warming. The resulting death toll is measured in millions of species.

What remains unclear is the degree to which humans are now repeating this bloodletting, to the extent that we are about to set off a sixth extinction wave. If so, we will be the first single, biological cause of this kind of catastrophe. "If you add up the numbers of species that have been wiped out over the past few hundred years, then you find the figures fall well short of a mass extinction," said MacLeod. "It is only when you look at the numbers of creatures that are poised at the brink of eradication does the picture become alarming."

Tigers, coral reefs and all the marine life they support, amphibians such as the golden frog of Panama, orang-utans, sharks, mountain gorillas, the marine iguanas of the Galápagos, albatrosses, chimpanzees and thousands of other creatures now face obliteration: hunted, rendered homeless, and poisoned by humans.

More to the point, this predation has been going on, not for hundreds of years, but for tens of thousands of years.

Whenever Homo sapiens has moved into new territory, this has been followed quickly by the disappearance of most large land mammals, palaeontologists have found. For example, the Clovis people, ancient hunters armed with fearsome stone-tipped spears, arrived in North America 12,000 years ago.

A total of 75 species, including woolly mammoths, mastodons, four-horned antelopes and lumbering sloths the size of giraffes were killed off almost immediately. A thousand years later, the slaughter continued in South America when humans arrived there.

The glyptodon (a giant armadillo-like animal), several species of rodent and various llama-like animals were wiped out. And a similar bloodbath occurred in Australia with the arrival of the first members of Homo sapiens.

In short, humanity has a great deal of blood on its hands, spears and guns. Whether we maintain this kind of eradication of our fellow Earthlings remains to be seen. Most experts predict grim times, an outcome that will provide Kolbert with the core of her ambitious look at the fate of our planet – and at the fate of the animals who are trying, unsuccessfully, to share it with human beings.