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A drawing of one of the teeth discovered by Charles le Moyne. The first published mention of the bones is on a map entitled Carte de la Louisiane Cours du Mississipi et Pais Voisins (Map of Louisiana, the Course of the Mississippi, and Neighbouring Countries). It is dated 1744 and was prepared by ‘N. Bellin‘ (Jacques-Nicolas Bellin 1703-1772).
A drawing of one of the teeth discovered by Charles le Moyne. The first published mention of the bones is on a map entitled Carte de la Louisiane Cours du Mississipi et Pais Voisins (Map of Louisiana, the Course of the Mississippi, and Neighbouring Countries). It is dated 1744 and was prepared by ‘N. Bellin‘ (Jacques-Nicolas Bellin 1703-1772).

The Sixth Extinction: The world has endured five mass extinctions. Can we survive a next one of our own making? Add to ...

  • Title The Sixth Extinction: An Unnatural History
  • Author Elizabeth Kolbert
  • Genre science
  • Publisher Henry Holt and Co.
  • Pages 336
  • Price $32

In 1739, a company of French soldiers together with a few hundred of their Native American allies were heading down the Ohio Valley en route from New France to Louisiana when they came across a sort of natural time capsule.

When the troops stopped to camp downriver from present day Cincinnati, some of the natives headed off into the woods to hunt. A few miles away, they found a strange marsh full of animal bones. The marsh had apparently ensnared all manner of beasts unfortunate enough to have wandered into its pungent and muddy waters – among them a creature with 10-pound teeth, an enormous tusk and an elephantine thigh bone.

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The commander of the company was Charles le Moyne, the second Baron de Longueuil, and governor of Montreal. When presented with the teeth, tusk and bone, he was sufficiently impressed to take them along for the rest of the expedition. Reaching New Orleans after many mishaps, Longueuil shipped the strange finds off to France and their ultimate destination, the personal collection of King Louis XV.

Jump to 1795 – not long after the French Revolution abruptly and violently eliminated the French monarchy. By then, the king’s collection had become the Muséum national d’histoire naturelle and Longueuil’s curious specimens had come to the attention of a 25-year-old zoologist named Georges Cuvier.

While puzzling over what he saw, Cuvier made an intellectual leap that upended a piece of conventional wisdom as old as Aristotle: the assumption that the animals we know today are the only animals Earth has ever known. Cuvier showed it could not be so. While the remains plucked from the Kentucky marsh were elephant-like, they were not exactly of an elephant. So what were they? Cuvier argued that they belonged to an espèce perdue, a lost species.

In his study, Cuvier had come nearer than any of his predecessors to perceiving the biological guillotine of extinction. And the mysterious, big-toothed creature – which he dubbed “mastodon” – would turn out to be just one of its many victims.

Since Cuvier’s seminal insight, scientists have come to understand that countless species have fallen by the evolutionary wayside as part of the normal course of things. Most of the time, the rate of extinction is slow and steady. For mammals, it works out to about one species among thousands passing into oblivion every 700 years.

But some disturbing exceptions have also come to light. The fossil record unequivocally shows that on five separate occasions during the past half-billion years, vast numbers of the world’s species – up to 95 per cent in the most extreme case – vanished in a geological instant, leaving behind a dramatically diminished biosphere. The precise causes of these mass extinctions are a matter of ongoing scientific debate, though the fifth and best known (the one that took out the dinosaurs and cleared the way for the rise of mammals) is known to have coincided with a direct hit from an asteroid.

Such cataclysmic events, with their ferocious power to rewrite the future of life across an entire planet, are all but unimaginable. Yet imagination is hardly required. If we look around, we can see we are in the midst of another such mass extinction right now. What’s more, writes journalist Elizabeth Kolbert in The Sixth Extinction: An Unnatural History, we are not only “witnessing one of the rarest events in life’s history, we are also causing it.”

The term Sixth Extinction has been in circulation since 1996 when anthropologist Richard Leakey and science writer Roger Lewin popularized it in a similarly titled book. Now, Kolbert, a staff writer at The New Yorker who is known for her series of brilliant pieces explaining the science and politics of climate change, picks up the theme and gives it a new and urgent focus.

Taking readers on a whirlwind tour across continents and eons, Kolbert’s destination is the front line of biological upheaval. In the process, she uncovers what scientists have learned about the process of extinction, and what it may portend for the future of life on Earth. The subject is well suited to Kolbert’s signature blend of vivid field reporting, fascinating excursions into history and clear explanations of technically complex research. The result is a troubling yet riveting examination of what happens when one species throws a spanner of epic proportions into the delicate machinery of global biodiversity. As Kolbert notes: this time, we’re the asteroid.

“No other creature has ever managed this, and it will, unfortunately, be our most enduring legacy,” Kolbert writes.

The notion that we are wreaking havoc on the planet is hardly a surprise. The impact of Kolbert’s approach is in showing how widespread and unintended are the consequences of our sudden and startling rise as the global grim reaper.

It’s not just about paving paradise, to paraphrase as Joni Mitchell. While we are indeed encroaching on wilderness at every turn, all the parking lots in world can’t account for the epic changes that are under way. Simply by going about our daily business, we’re rewiring the ecological circuitry of the planet, and triggering blackouts aplenty.

Kolbert demonstrates this effect at her first stop, a conservation centre in Panama that serves as a “frog hotel” for endangered amphibians. But like the Hotel California, the centre is a place where the guests can never leave. Beyond its walls, the tropical streams that formerly teemed with colourful species like the Panamanian Golden Frog have been emptied of its amphibian inhabitants, a wholesale disappearance that swept over the area a decade ago.

The culprit has turned out to be a kind of fungus that infects frogs’ skin and deprives them of electrolytes. As Kolbert explains, “this causes them to suffer what is, in effect, a heart attack.” By the time it was noticed, the fungal wave was already a global phenomenon. Largely because of it, amphibians – an ancient and hardy group that sailed through with barely a wrinkle when the dinosaurs perished – are now the most endangered class of animals on Earth.

Significantly, unlike the hapless dodo or the passenger pigeon, the frogs that are vanishing before our eyes are not the direct target of human action. Yet, their demise is just as surely the product of human invention, thanks to modern air travel, which connects pathogens to potential hosts in ways that have not been possible since all the continents were together in one land mass. One theory posits that the disease was transported around the globe by shipments of African clawed frogs, which can carry the fungus but are unaffected by it, and which were widely used for pregnancy tests throughout the 1950s and 1960s.

Using airplanes to recreate a “New Pangaea” is an immediate effect of our far-reaching presence. But longer term and more profound transformations are also in motion. The entire suite of changes has so altered the planet that some scientists argue we are living in a new geological era – dubbed the Anthropocene – in which it is impossible to separate what’s happening on Earth from what we’re doing to it.

Kolbert’s most poignant chapters deal with a subject she knows well, the effects of climate change. Here, we have a sneak preview of the ecological pressures that are most likely to drive the sixth extinction for centuries to come.

While visiting researchers at Australia’s Great Barrier Reef, Kolbert capture a sense of the fragility of an entire ecosystem that is poised to be undone by ocean acidification. This is extinction supersized. In an effort to capture what it means, Kolbert quotes from one researcher who suggested in a recent Nature paper that by 2050, based on current trends, visitors to the Great Barrier Reef will arrive to find only “rapidly eroding rubble banks.”

Such assessments could make for a gloomy read but but Kolbert manages to avoid being depressing or preachy by keeping her focus on the science, which is engrossing, and the scientists she meets along the way. Together, they form a remarkable cast of characters, all grappling with an unprecedented moment in the story of life.

It’s also a story that is propelled by a cliffhanger ending. While humans have become the largest force at work on the planet, we remain fundamentally dependent on its systems for our own survival. Just because we can start a mass extinction doesn’t mean we can outlast it.

As Leakey and Lewin wrote: “Our inability to imagine a world without Homo sapiens has a profound impact on our view of ourselves; it becomes seductively easy to imagine that our evolution was inevitable. And inevitability gives meaning to life, because there is a deep security in believing that the way things are is the way they were meant to be.”

Such hubris leads to a kind of blindness. Until Cuvier, it prevented scientists from recognizing the truth in a pile of exotic bones. Unless we shake it off altogether, it will prevent us from recognizing the truth of our own situation: that we are walking a tightrope without a safety net. Kolbert is telling us its time to look down. The view is scary but it’s also amazing.

Ivan Semeniuk reports on science for The Globe and Mail.

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Follow on Twitter: @ivansemeniuk

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