The Sixth Extinction: An Unnatural History

Elizabeth Kolbert combines the sharp observational powers of a field biologist with the literary skill of a seasoned and thoughtful writer. In her previous book “Notes from a Field Catastrophe”, she travelled to far-flung parts of the globe to dig up stories on the deleterious effects of climate change. In her latest book she combines similar reporting from around the world with chapters from the history of science to bring us a noteworthy account of one of the most spectacular and important stories of biology and history – mass extinctions. There have been five documented big extinctions in history, with the most popular one being the death of the dinosaurs that was memorably caused by a meteorite. However we are probably now in the throes of a sixth extinction, and as Kolbert documents, at least parts of it are being caused by human beings’ destructive tendencies and our unquenchable thirst for natural resources. The concern for extinctions is not merely a discussion for the drawing rooms of bleeding-heart environmentalists; as a chemist, I am well-aware that about half of all drugs on the market are derived from natural sources. Every time we kill off another marine sponge or frog, we may be depriving ourselves of the next breakthrough drug against cancer or AIDS.Kolbert starts by telling us how we came to know about extinctions in the eighteenth century. It took a long time for scientists and the public to actually believe in such devastating events, simply because of their magnitude. It was Georges Cuvier, a French naturalist, who painstakingly collected fossils and bones of giant and exotic creatures from around the world and turned conjecture into reality. By cataloging their sheer abundance Cuvier convinced everyone of the reality of worlds lost in time that were completely different from our own. Charles Darwin and Charles Lyell who came after Cuvier also debated extinctions; but since Darwin’s theory required very gradual changes over time, he could not quite fathom how entire species of animals could disappear in an evolutionary eyeblink. Kolbert also tells the fascinating story of the Alvarez father-son duo who discovered the potential reason for the extinction of the dinosaurs by measuring the startlingly high concentration of iridium – an element found in abundance only in meteorites – in certain clay layers.The real meat of the book is Kolbert’s travels to different parts of the world and her reporting of what seem like extinctions of specific species. In one chapter she explores the impact of climate change on ocean acidification – one of the more neglected aspects of the global warming debate – on coral reefs. Ocean acidification is a consequence of simple chemistry; when carbon dioxide dissolves in water it lowers its pH, and the resulting acidic solution starts to eat away at corals which are composed of calcium carbonate.Last year I was in Hawaii and one of the most revealing experiences I had there was snorkeling around the island where Captain Cook was killed. Peering through the goggles, I could see not only a spectacular ecosystem of fishes, tube worms, sea cucumbers, jellyfish and other denizens of the deep but also how critically dependent all of them were on the coral reefs. The worms were permanently latched on to the reefs and the fishes were constantly kissing the surface with puckered lips, consuming the plant and microbial material deposited in the oxygen-rich pores of the intricate structures. Clearly the reefs support many living worlds, and as Kolbert finds out first-hand, these worlds are being depleted by ocean acidification. Even those who may be skeptical of the warming effects of CO2 emissions should take this impact very seriously. And as I mentioned before, nor is this concern purely moral; marine sponges have been the source of some of the most promising drugs against cancer and will continue to be so.Kolbert also explores the disappearance of other species spanning the spectrum of species diversity, from birds to frogs to mammals. In documenting this she travels to caves in Italy, rain forests in Central Africa and even a location in – of all places – suburban New Jersey, where traces of the K/T boundary event that killed off the dinosaurs can be found. Fungal infections seem to be a leading and particularly concerning cause of several current extinctions, most notably those of New England bats and Panamian golden frogs. Amphibians are more affected than almost any other species partly because of their sensitive skin. In a vivid chapter Kolbert locates an artificial ecosystem set up by scientists in Panama where the last few hundred golden frogs survive. By now the fungus is so rampant in their natural environment that releasing them outside would be fatal. These brightly colored creatures, nurtured by their human caretakers, are the last surviving members of their tribe and on the brink of disappearing from the face of the planet. A similar poignant chapter introduced us to a male Hawaiian crow, who just like the golden frogs, is part of a species that exists only in a zoo. All attempts by the zoo personnel to induce this crow to mate have been unsuccessful so far and one does not know how much longer his thread will stay unbroken.Kolbert wisely stays away from attributing many of these species disappearances to human activity. But in many cases there is strong evidence that does link human activity to rapid species depletion. In this context deforestation may be an even bigger threat than climate change; indeed, a universal mathematical scaling law linking number of species to area seems to encapsulate the impact of deforestation. So is the introduction of non-endemic species by air and sea travel which when introduced into a new ecosystem find themselves free of predators and start decimating the local population; the brown tree snake which was introduced in Guam and which literally ate its way through several bird and amphibian populations is a noteworthy case. The voracious zebra mussel which has wreaked havoc in waterways in the US is another example.The impact of humans is undeniable, and in measuring this impact we see the sometimes cruel and indifferent streaks of inhumanity which mark us as one of the few species on the planet which takes pleasure in killing others. Particularly barbaric was the butchering of the flightless Great Auk to extinction in Northern Europe in the nineteenth century; Kolbert talks about how hungry sailors devoured the auks not only by dunking them in boiling water but also by using them as fuel for the fire underneath. One of the simple reasons why humans can quickly render larger animals extinct is because of their slow breeding rate. This explains the disappearance of the megafauna in New Zealand for instance, where the hunting of the large, flightless moa provides a stark test case. In ecosystems untouched by humans, whatever disadvantages are suffered by creatures because of their slow reproductive rate can be compensated for by their larger size and strength. When intelligent human beings wielding weapons arrive on the scene, the equation radically changes. This is precisely why larger animals like lions, tigers and apes are the most threatened species today.Perhaps the most fascinating aspect of humans’ devastating impact on other species emerges when we look not to distant species but to a very close one – the Neanderthal. One of the most significant discoveries in science during the last few years has been the realization that after encountering Neanderthals in Europe and Western Asia about forty thousand years ago, Homo sapiens first interbred with them and then somehow killed them off. There is something deeply creepy about this fact. As revealed by groundbreaking recent work on sequencing Neanderthal DNA, virtually all of us have between 1 and 4 percent of this DNA in our own genome. We may even have inherited a few genes for disease from our close cousins. This work has been made possible largely by the efforts of Swedish geneticist Svante Paabo who Kolbert interviews, and his recent book provides a fascinating look at the sequencing of the Neanderthal genome.What caused Neanderthals to go extinct while we lived? War certainly could be one reason; after all population sizes as well as mortality rates then were quite low. Perhaps Neanderthal populations were already on the brink of extinction when humans met them so purely on a statistical basis they may have been unlikely to survive for too long. My favorite explanation is disease. It is very much possible that interbreeding between modern humans and Neanderthals made the latter more susceptible to certain diseases passed on from humans. Neanderthals could also have been more prone to certain diseases to begin with. There is also some evidence that humans were more creative and intelligent than Neanderthals, so we may have been better equipped to deal with diseases than our “less evolved” cousins. Whatever the reason, the co-existence of humans and Neanderthals followed by their disappearance is another data point on the table of extinctions in which humans might have played a dominant role.The whole saga of extinctions also conceals a profound irony. In death there is life. The same great five extinctions that killed off more than 90% of species on the planet also opened up ecological niches and resources to previously suppressed creatures. Dinosaurs made room for mammals and amphibians and led to the evolution of human beings. It is also almost poetically ironic that a few members of the same human species that killed off so many of its evolutionarily distant and close cousins are also making heroic efforts to preserve the remaining members of certain species in zoos and other ecological enclaves. We don’t know how this story of extinctions is going to end. Perhaps it will end with humans killing most other species on the planet by breaking the chain of interdependencies between various animals and plants. If we do this we may be killing ourselves by destroying the intricate web of natural resources that allows us to farm, feed and clothe the world. Or perhaps we may kill ourselves more directly through climate change, overpopulation or nuclear war. In any case, the history of extinctions tells us that the planet will survive. Nature always finds a way.*First published on the Scientific American Blog Network.

The Sixth ExtinctionI didn’t rush to read Elizabeth Kolbert’s book, The Sixth Extinction, because I imagined it would be a gloomy expose on the unfortunate consequences of way too much half-baked cleverness — and it was. But it’s also a fascinating story about the long saga of life on Earth, and the unclever antics of the latest primate species. It’s an outstanding book.We have soared away into a fantasy world, where godlike humans spend their lives creating brilliant miracles. But when observed in a 450 million year timeframe, from this moment when a new mass extinction is gathering momentum, the wonders of progress and technological innovation lose their shine. Kolbert rips off our virtual reality headsets, and serves us powerful medicine, a feast of provocative news.Today, the frog people are not feeling lucky. They have lived on this sweet planet for 400 million years, but many are now dying, because of a fungus called Bd. This fungus can live happily in the forest on its own, without an amphibian host, so endangered frogs rescued by scientists cannot be returned to the wild. The crisis began when humans transported frogs that carried the fungus, but were immune to it. There was money to be made in the frog business, and so the fungus has spread around the globe.This is similar to the chestnut blight of a century ago. Entrepreneurs profitably imported chestnut seedlings from Asia. The Asian species was immune to the fungus it carried. American chestnut trees were not immune, and four billion died, almost all of them. The fungus persists, so replanting is pointless.North American bats are dying by the millions from white-nose, caused by fungus that is common in Europe, where bats are immune to it. It was likely carried across the Atlantic by a tourist who dropped some spores in Howe Caverns, in New York. By 2013, the die-off had spread to 22 U.S. states and five Canadian provinces.Welcome to New Pangaea! Once upon a time, long before we were born, all seven continents were joined together in a single continent, Pangaea. Over time, it broke apart, and ecosystems on each continent evolved in a unique way. In recent centuries, highly mobile humans have moved countless organisms from one ecosystem to another, both deliberately and unintentionally. The seven continents no longer enjoy the long-term stability provided by isolation.On another front, many colonies of humans have become obsessed with burning sequestered carbon on an enormous scale. This is overloading the atmosphere with carbon, which the oceans absorb and convert to carbonic acid. Carbonic acid is a huge threat to marine life, except for lucky critters, like jellyfish. The world’s coral reefs are dying.Tropical rainforests are treasure chests of biological diversity. Tropical oceans generally are not, because of low levels of nutrients like nitrogen and phosphorus. Coral reefs are the shining exception. They provide habitat for thriving ecosystems, home to more than 500,000 species. This reminded me of beaver ponds, which are also sanctuaries of abundant life.Coral polyps and beavers are excellent examples of reciprocity. They create relationships that are mutually beneficial for many species. Reciprocity is a vital idea that most human cultures have forgotten. Our dominant culture has no respect for the wellbeing of ecosystems. It has a tradition of displacing or exterminating the indigenous species on the land, and replacing them with unsustainable manmade systems.Evolution is fascinating. Rabbits and mice have numerous offspring, because they are vulnerable to predators. Other species have deflected the predator challenge by evolving to great size, like mammoths, hippos, and rhinos. Big critters have long lifespans and low birth rates. This made them highly vulnerable when Homo sapiens moved into the neighborhood.Kolbert imagines that the megafauna extinctions were not the result of a reckless orgy of overhunting. It probably took centuries. Hunters had no way of knowing how much the mammoth population had gradually dwindled over the generations. Because they reproduced so slowly, they could have been driven to extinction by nothing more than modest levels of hunting. An elephant does not reach sexual maturity until its teens, and each pregnancy takes 22 months. There are never twins. Deer are still with us, because they reproduce faster.Sadly, Neanderthals are no longer with us. They lived in Europe for at least 100,000 years, and during that time, their tool collection barely changed. They probably never used projectiles. They have acquired a reputation for being notorious dimwits, because they lived in a stable manner for a very long time, and didn’t rubbish the ecosystem. Homo sapiens moved into Europe 40,000 years ago. By 30,000 years ago, the Neanderthals were gone. The DNA of modern folks, except Africans, contains up to four percent Neanderthal genes.Homo sapiens has lived in a far more intense manner. In the last 10,000 years, we’ve turned the planet inside out. Kolbert wonders if there was a slight shift in our DNA that made us so unstable — a “madness gene.” I wonder if we’re simply the victims of cultural evolution that hurled us down a terrible path. If we had been raised in Neanderthal clans, would we be stable, sane, and happy?Kolbert laments, “The Neanderthals lived in Europe for more than a hundred thousand years and during that period they had no more impact on their surroundings than any other large vertebrate. There is every reason to believe that if humans had not arrived on the scene, the Neanderthals would be there still, along with the wild horses and wooly rhinos.”Cultures have an amazing ability to put chains on our mental powers. Kolbert describes how scientists (and all humans) typically struggle with disruptive information, concepts that bounce off our sacred myths. Bizarre new ideas, like evolution, extinction, or climate change, are reflexively dismissed as nonsense. As evidence of reality accumulates, increasing levels of absurd rationalizations must be invented. Eventually, someone actually acknowledges reality, and a paradigm shift is born.For most of my life, human extinction has not been on my radar. By the end of Kolbert’s book, readers understand that our extinction is more than a remote, theoretical possibility. What is absolutely certain is that we are pounding the planet to pieces. Everything is connected, and when one type of tree goes extinct, so do the insects that depend on it, as well as the birds that depend on the insects. When the coral polyps die, the coral reef ecosystem disintegrates.The sixth mass extinction is clearly the result of human activities. The driving forces include the things we consider to be our great achievements — agriculture, civilization, industry, transportation systems. This is highly disruptive information, and everyone is working like crazy to rationalize our nightmares out of existence. Luckily, a number of people, like Kolbert, are beginning to acknowledge reality. Will there be a paradigm shift? Will we walk away from our great achievements, and spend the next 100,000 years living in balance with the planet?

highly recommended, I should have read this when it came out. I have bought ihis for and recommended it to many people.

A fascinating look at the evidence for the world currently being at the start of a sixth extinction event, and how extinctions are driven by human activity. There's a background to the theories of evolution, and an explanation of why our assumptions of the resilience of the earth's systems may be horribly wrong. The only odd note in the book is the author's writing style, where scientific explanations and historical background are shot through with very specific, apparently-irrelevant personal details: one person she meets has different-coloured eyes; kangaroo meat forms part of the meal taken with a bunch of Israeli scientists; she has a dream about a frog smoking a cigarette. But perhaps this is the extreme of a writing style that, while humanising the experts, in the process imparts a great deal of information, not just about them but specifically about their work. The scope of this book is remarkably broad, and the author does a very good job of explaining both how extinctions are taking place, and how they are being researched. I bought this expecting a far more straightforward "science" book, but it was a surprisingly compelling read.

If you want to put climate change and the climate emergency into the context of the history of the earth then this is a worthwhile read. Chapter after chapter full of fascinating views from experts, some of whom agree some not but always interesting. Elizabeth's reports and observations from her travels bring alive what has happened over the millennia and is referenced to the situation today where so many flora and fauna are becoming extinct almost by the hour. Where will humans end up? She muses but leaves conclusions to us, the readers. Full of information, puzzles and facts but never dry or boring.

I bought this book as it was on Bill Gates' summer reading list. What I read was shocking.I have been to the Great Barrier Reef but found out that, since I was there, about half of it has gone due to ocean acidification as a result of an increase of CO2 in the atmosphere.We learn that humans have always been destructive, making over 150 mega fauna mammals (mammoths etc.) extinct due to overhunting over the millennia. As our population grows and we travel around more, we have brought extinctions up to around 1,000 times the background rate. At this rate, the world will be very different in 35 years and unrecognizable by the end of the century.We are doing the same amount of damage as an asteroid and the only way to reverse it, or even slow this phenomenon is through education. This is what this book provides and I sincerely believe it should be compulsory reading in schools.

This is a beautifully written book about the way that humans in the last two hundred years or so have been ruining the world. It was interesting to read this book after reading "Factfulness" which is full of hope that the problems of the world can be solved. I fear that the surging populations of Asia, Africa and South America and their demands for a better life will make it impossible to reverse the tide of climate change and rising acidity in the oceans which will dominate life over the coming decades.

Purchased through a third party, maybe because the title is out of print. I can't understand why it would be as it is essential reading for anyone with an interest in the environment, wildlife, Earth science etc. It is well informed and written stylishly. Although a detailed discussion of extinction and fully referenced, it engages the reader throughout and I found it difficult to put aside.