The Sixth Extinction: An Unnatural History

"When the world changes faster than species can adapt, many fall out. This is the case whether the agent of change drops from the sky in a fiery streak or drives to work in a Honda. To argue that the current extinction event could be averted if people just cared more and were willing to make more sacrifices is not wrong, exactly, but it misses the point. It doesn't matter much whether people care or don't care. What matters is that people change the world." Thus is the premise and sad reality stated in Elizabeth Kolbert's "The Sixth Extinction." Part travel log, part history of the world and part zoological introduction to some wondrous creatures, yet at all times a sobering look at what "one weedy species" (mankind) has done to our fair planet, Kolbert's book is a must read for anyone interested in knowing what the not too distant future holds. I saw Kolbert interviewed on Jon Stewart about a month ago and became intrigued by this book. After a couple of entertaining novels featuring shady characters and twisting plot lines I was ready for a different kind of reading experience. "The Sixth Extinction" was not as laborious a read as I feared. Kolbert keeps the writing brisk and the science light. And she takes us around the world as she visits places as diverse as the Coral Reefs off Australia, bat caves in New England and an island off the coast of Italy. Along the way we meet some splendid creatures, many of whom are already extinct or well on their way. Plus we learn the history of the first five mass extinctions, how they happened and just as importantly how scientists have been able to figure out how something that happened hundreds of millions of years ago took place. The part of the book that I found most surprising is that it's not just climate change and extreme hunting that has killed off so many species. It is the movement of man around the world (and the introduction of new species into a region where they never existed that this movement allows) that has threatened so many creatures. The book opens with the case of frogs in a South America who are dying off at an alarming rate due to a fungi that was introduced into the forests of Panama just a few years ago. The fungi is from Asia where the amphibians have evolved through the millennia to be immune from it. But in South America, the frogs never needed whatever mutation Asian frogs have and thus many species there (which are hundreds of millions of years old) have become extinct. Similar situations are happening to the bat population in the US and many other creatures. And that, as Kolbert points out is why all the "Save the Whales" movements in the world will not completely stop this sixth extinction. Kolbert also gracefully spells out the irony of man, how so many of our actions lead to these latest extinctions - yet how so many work so diligently to avoid them. (The scientist giving a handjob to a crow to extract semen being perhaps the clearest example of this "diligent" work). Ultimately the book cannot answer the question that surely every reader has: will we (mankind) alter the world to such a degree that even we become extinct? Will we create an environment that no longer supports us? Or will we, as history's greatest innovators, continue to find a way to save ourselves (even if as the book says that means establishing communities in space should earth someday become unlivable). Surely this situation will not happen in our lifetime, and probably not in our children's lifetimes or their children's lifetimes. Thousands of years are immense when measured by man. In earth time, they are but a blink of an eye. If you want an interesting book, a readable story with some amazing insights, I'd highly recommend "The Sixth Extinction." Meanwhile I'm going to bury my head back in the sand and return to novels with shady characters. Even when the endings are depressing they aren't this depressing.

Elizabeth Kolbert somewhat goes on an adventure while researching the topics in this book. This made The Sixth Extinction exciting and full of knowledge and history. In the beginning, Kolbert goes into great detail about “The Big Five” mass extinctions in Earth’s recorded history and the impacts/significance of each. Kolbert also explains the history of the concept of extinction through a human perspective. After explaining how extinction was significant, she insinuates that humans have created a new geologic epoch, referred to as the Anthropocene. In this new epoch, Kolbert notes that humans have spread to every corner of the Earth, have become the most invasive species on Earth and are the only creatures on Earth capable of changing the composition of the atmosphere. This changing of the atmosphere has in turn affected climate and has changed the chemistry of the oceans in the process. I don’t think Kolbert’s goal was to necessarily convince people that climate change was causing The Sixth Extinction, but rather explaining the significant effects that humans can have on the environment, which is leading to massive die offs of important species. That being said, climate change is obviously exacerbating the process of extinctions globally. Overall, Kolbert does an excellent job of getting her hands dirty, traveling all of the world to speak with scientists that are researching rapid extinctions, picking up dead bats and snorkeling in the Great Barrier Reef. The book is very informative, easy to understand, and eye opening.

The Sixth Extinction I 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?

Yes, human-caused extinction is upon us in full force. As science journalist extraordinaire Elizabeth Kolbert tells it, we humans have been killing whatever we could whenever we could since the beginning of our tenure here on earth. First the mastodons, the giant sloths, the great flightless birds, the woolly rhino, then the whales, the gorillas, the tigers, the buffalo, etc. The first cause was ignorance. Primitive humans just didn’t know that they were destroying the source of their subsistence until they had to move on. Today we know the truth. And that truth is there is nowhere to move on to. This book is a detailed and fascinating delineation of just what we are doing to the planet and how. From the fishes in the sea to the polar bears on the ice: all fall down. Why? Willful ignorance, stupidity, and the devil take tomorrow. (But it might be said, so what if we kill off all sorts of creatures great and small? We don’t need them. We have our pigs and cows and chickens. We grow corn and soy. Yes, the little foxes are cute and the lions magnificent. But we have zoos and preserves. After you’ve seen a few elephants you don’t need to see vast herds of them.) This is the view of many people in high places in government and at the helms of giant corporations whose main concern is staying in power and improving the bottom line. But here’s the rub: with the extraordinary rate of the current extinction what we might be left with is nearly sterile oceans, stunted scrub forests, destroyed ecologies and starving humans at one another’s throats. Combine that with global warming and desperate leaders flinging nuclear bombs around, and yes, Chicken Little, the sky is falling. Okay, rant over with. Let me say a few things about this splendid book that is so readable and so full of information, humor and the kind of passion that lights up the pages. Kolbert combines research, interviews and fieldwork into a very readable, vivid and informative narrative that is so good that…well, she won the Pulitzer Prize for this book in 2015. Some notes and quotes: “The reason this book is being written by a hairy biped, rather than a scaly one, has more to do with dinosaurian misfortune than with any particular mammalian virtue.” (p. 91) “Warming today is taking place at least ten times faster than it did at the end of the last glaciation, and at the end of those glaciations that preceded it. To keep up, organisms will have to migrate, or otherwise adapt, at least ten times more quickly.” (p. 162) Kolbert notes that during the Pleistocene (2.5 million years ago to about 11,700 years ago) “…temperatures were significantly lower than they are now…,” mainly because the glacial periods tended to be longer than the interglacial periods. What this means is that most life forms are probably not going to be able to deal with the heat “...since temperatures never got much warmer than they are right now.” In other words, we are experiencing an accelerated catastrophe. (p.171) Kolbert describes the red-legged honeycreeper as “the most beautiful bird I have ever seen.” (p. 178) So naturally I had to Google it. It is indeed beautiful. The reader might want to take a look. It’s very blue with some neat black trim and those incongruous red legs! Kolbert observes that we are creating a New Pangaea because our global transport systems are sending plants and animals all around the globe. Instead of the continents moving closer together the plants and animals are moving closer together as on a single continent. (p. 208) A joke: after the journal “Nature” published proof of the existence of the Denisovan hominids because of a DNA-rich finger found in southern Siberia, there came a newspaper headline: “Giving Accepted Prehistoric History the Finger.” (p. 253) As to the “controversy” over what killed off the megafauna in e.g., North and South America, in Siberia, in Australia, Kolbert minces no words and comes down strong on the likely suspect—us. And as for the Neanderthal, ditto. See chapters XI and XII. She writes: “Before humans finally did in the Neanderthals, they had sex with them.” She notes that “most people today are slightly—up to four percent—Neanderthal.” (p. 238) Personally, according to “23 and Me,” I am 3.8% Neanderthal. --Dennis Littrell, author of “Understanding Evolution and Ourselves”

If you're looking for a well thought out book that may change your perspective on humans and increase your observation of the world around you then this book is perfect. Elizabeth Kolbert's detailed analysis and writing style throughout the Sixth Extinction leaves the reader feeling informed and wondering about the future of the human race. The book explores the past extinctions and the various causes, then hones in on the current one that we are experiencing today. I feel that everyone should read this book as the topics discussed are now more important than ever. While species extinction is a commonly known idea that gets thrown around, people don't often talk of the specifics surrounding it. Everyone can get something out of this book if they are willing to put in the effort. The book is slightly more dense, containing many scientific terms and some parts read more like a research paper, but that adds to the level of detail the book goes into on each specific topic or species. I've talked about numerous topics from the book with friends and family, particularly the effect white nose syndrome has had on the bat population that's highlighted the effect of diseases spreading through travel and trade. To me, the making of a good book is if you continue to think about it after you've finished. I still find myself wondering about some of the ideas brought up and about past events that I never knew happened until I read this book. I would highly recommend this to anyone as this is a topic that is increasingly relevant today and something that would get the conversation started on what we could do to try and reduce our impact on the world around us.

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.

Extinctions happen, Elizabeth Kolbert tells us. There have been five major extinctions, each brought about by one cause or another. Different causes, like climate change, for instance. Or volcanism, manifested by the Siberian Traps and the Deccan Traps. And the bolide impact at Chixchalub, which wiped out all non-avian dinosaurs and numerous other life forms. Catastrophic events that eradicated millions of species over half a billion years. None of it man made. But in the blink of a eye in geological time, humans have been a major force in extinctions, directly or indirectly. Kolbert details the recent rapid demise of toads and frogs in various places around the globe. Turns out it's caused by a fungus. A similar situation, also involving a fungus, is killing off huge numbers of bats in various locations. The fungi travel globally via modern human transportation means, like ships and airplanes. Humans encroach on some species environments by cutting down forests and replacing them with crops and livestock. And we deliberately kill off every last member of a species. Elizabeth doesn't mention the demise of bison in America, which once thundered across our plains sixty million strong. They were killed, often for sport, until only a couple of hundred survived, before laws protected them. And the passenger pigeons, so numerous that a flock of them passing overhead in America took more than an hour to complete a flyover, with millions of birds. The last of them, a female named Martha, died in an American zoo over a century ago. Invasive species are taking over environments and displacing native species. Kolbert discusses the zebra mussel in this regard. But there are so many more examples. Like the pythons that escaped a pet store in south Florida due to Hurricane Andrew and took up residences in the Everglades. By now there are tens of thousands of them, and they are wiping out native animals there. She talks about climate change and its destructive effects on wildlife. It's evil twin is ocean acidification. The pH of ocean water is about 8.2, slightly alkaline. But the pH is dropping, to 8.1, and near thermal vents down to below 8.0. Some species can handle this. Some cannot, like the calcified, animals that use calcium for their structures. Like sea urchins, starfish, limpits, barnacles, for instance. She is big on diversity. We're losing it, she says. But are we? What she doesn't cover is speciation, the opposite of loss of species. I direct her attention to Lake Victoria in Africa, the world's largest tropical lake. In it reside some 500 species of cichlid fish. They maintain their separation by species through different shapes and color patterns and size, and by feeding habits and water depth. She maintains that when humans start inhabiting places where no people ever lived, many native species die off. Like in Madagascar some two thousand years ago when humans first got to the island. In a couple of hundred years the large bird, twice the size of an ostrich, was gone. So too the huge lemur, the size of a gorilla. The same thing happened to animals, especially large one, when humans got to Australia, over fifty thousand years ago. And in New Zealand when people got there a thousand or so years ago. North America too saw it happen when humans from Siberia came across the Bering land bridge about sixteen thousand years ago. Within a few thousand years at most the large animals were wiped out, like the ground sloth, mammoth, mastodon, cave bear, dire wolf, saber tooth cats, among others. The book is a must read.

This is an excellent book, perhaps the best recent book on global warming. It puts global warming into a much longer context than usual. Since the flowering of life in the Cambrian, which started 540 million years ago, there have been five times when life almost died out because of catastrophes that affected Mother Earth. The last of these occurred about 66 million years ago at the end of the Age of Dinosaurs. This was due to an asteroid about six miles in diameter which hit the earth leaving the Chicxulub Crater on the Yucatan Peninsula. This caused an immediate climate change with plants being unable to undergo photosynthesis the following year and a die-off of most of the large animals including the dinosaurs. The sixth extinction for which the book is named is the extinction brought about by man. The destruction of species started already tens of thousands of years ago, when hunter-gatherer societies killed the last of the mammoths and mastodons. As humans started civilizations in the Nile, Tigris and Euphrates Valleys they transformed the environment. Man simply used up all the environmental niches, replacing forests and savannas with cities. By 1798, when Malthus wrote his essay on the Principle of Population, the population of the world was less than a billion. By 1968, when Paul Ehrlich published the Population Bomb, world population was about 3.5 billion, and it is now approaching 8 billion. This population growth coincided with the industrial age, and Ehrlich’s book had proposed a simple mathematical argument. Ehrlich had reasoned that no positive growth, say 2% per annum, could be maintained indefinitely, that death rates would have to increase to balance birth rates. Among the possible ways in which growth would stop he mentioned starvation, running out of necessary resources, or overcrowding which might cause a breakdown of civil order. We now know that what will limit population growth is most likely the heating of the planet caused by a buildup of carbon in the atmosphere. The book by Kolbert describes the way in which overpopulation is leading to the dying out of species. Chapters are devoted to the Panamanian golden frog and the great auks which are already gone, and to the coral which will likely be destroyed by acidification of the oceans. A chapter is devoted to heroic efforts being made to save the rhinos. Another chapter describes how gradual warming causes various species of trees in the Amazon rain forest to gradually move to higher ground. As I read this book, I reflected on the most likely scenario moving forward. Politicians continually borrow against the future, building up budget deficits year after year in the belief that growth will erase the deficits. Yet as the earth warms, its carrying capacity will diminish. Population growth will be replaced by lower population due to much of the equatorial region of planet earth becoming less habitable. Economic growth will falter and the notion of perpetual growth will become untenable. Yet people somehow still cling to the notion of growth as a solution to all problems economic. Just as Ehrlich could not tell whether it might be starvation or environmental destruction that would be the binding constraint, we cannot know the details of how the end to growth will work out. Will there be a new dark ages? Will there be a reassertion of superstition? Will there be nuclear wars over resources? What is it that caused us to ignore Ehrlich’s warning, which makes the problem twice as difficult now as it was then? Why can we not see even now that we need not only to replace fossil fuels but also encourage humans to use birth control, so that we control our own population growth before a warming earth does it for us?