The central theme of The Sixth Extinction is, unsurprisingly, extinction. In the book, Elizabeth Kolbert examines the different ways that scientists have understood species extinction. In particular, she argues for the “catastrophist” theory of extinction. According to this theory, species do not go extinct slowly and gradually; instead, there are eras of planetary history during which global catastrophe causes many thousands of species to go extinct almost simultaneously. It is likely, she argues, that we are living in an age of mass-extinction caused by human attempts to reshape the environment. Kolbert’s analysis of the catastrophist theory leads her to ask an important question: given that humans may be causing a mass-extinction, what moral obligation do they have to their environment, and to other species?
In the first half of the book, Kolbert draws an important distinction between ordinary extinction and mass-extinction, based on Charles Darwin’s theory of natural selection. According to Darwin, plants and animals are locked in a constant competition for the Earth’s resources, particularly food and shelter. The result is that some species will succeed in feeding and protecting themselves, and will therefore bear offspring, while less successful species will fail to survive and have offspring, and will therefore go extinct. In such a way, extinction is an inevitable result of the fact that there are too many species competing for too few resources. While Kolbert doesn’t disagree with Darwin’s reasoning, she argues (citing many 21st century scientists) that there have been some eras in planetary history in which sudden environmental changes caused many species to die out suddenly. The most famous example of this is the extinction of the dinosaurs after an asteroid hit the Earth hundreds of millions of years ago, but Kolbert posits that there have been at least six major global catastrophes in the Earth’s history, each of which caused a mass-extinction.
While mass-extinction isn’t a uniquely contemporary phenomenon, Kolbert argues that the current age of mass-extinction is different from its predecessors because it’s manmade. Humans aren’t the only creatures to alter their environments, but they do so to a far greater degree than any other life form on Earth. Since the Industrial Revolution, humans have consumed billions of tons of coal and gas, greatly increasing the amount of carbon dioxide in the atmosphere. They have also cut down millions of trees, an act which scientists believe has already raised the Earth’s temperature. The effect of human activity on the environment has been enormous and devastating, particularly for other life forms. CO2 emissions have changed the acidity of the oceans and increased the temperature of the world’s coral reefs and rainforests, making it difficult, if not impossible, for thousands of species to survive. Kolbert argues that, if humans continue their behavior unchecked, rising temperatures and other environmental changes could result in the extinction of a huge chunk of the world’s species—perhaps even more than half.
Kolbert’s book is neither a diatribe nor an instruction manual: she lets readers make up their own minds about what humanity’s response to the Sixth Extinction should be, rather than telling them exactly what to do. Nevertheless, Kolbert personally seems to believe that humans have an obligation to change their behavior and protect endangered or at-risk species from dying out. Kolbert offers two main reasons for humanity’s obligation to other species, one selfless, the other selfish. First, she suggests that human beings have a moral obligation not to cause pain or harm to other beings, even if these other beings are non-human. Second, she suggests that human beings should not alter their environments because they’d be harming their own interests. Manmade climate change endangers human life by disturbing “environmental equilibrium” and unleashing new viruses and bacteria—and, more abstractly, by altering their own environments, humans are cheating themselves out of the world’s wonder and beauty. Ultimately, The Sixth Extinction argues that manmade extinctions are unlike anything in the history of the planet, and, as such, the book suggests that humans will need to change their behavior to an unprecedented degree.
Related Themes from Other Texts
Mass-extinction and Morality ThemeTracker
Mass-extinction and Morality Quotes in The Sixth Extinction
The process continues, in fits and starts, for thousands of years, until the species, no longer so new, has spread to practically every corner of the globe. At this point, several things happen more or less at once that allow Homo sapiens, as it has come to call itself, to reproduce at an unprecedented rate. In a single century the population doubles; then it doubles again, and then again. Vast forests are razed.
The history of life thus consists of "long periods of boredom interrupted occasionally by panic."
By the middle of the nineteenth century, many of [Georges Cuvier’s] ideas had been discredited. But the most recent discoveries have tended to support those very theories of his that were most thoroughly vilified, with the result that Cuvier's essentially tragic vision of earth history has come to seem prophetic.
… if there were four extinct species, Cuvier declared there must be others. The proposal was a daring one to make given the available evidence. On the basis of a few scattered bones, Cuvier had conceived of a whole new way of looking at life. Species died out. This was not an isolated but a widespread phenomenon.
Cuvier's essay was pointedly secular. He cited the Bible as one of many old (and not entirely reliable) works, alongside the Hindu Vedas and the Shujing. This sort of ecumenicalism was unacceptable to the Anglican clergy who made up the faculty at institutions like Oxford, and when the essay was translated into English, it was construed … as offering proof of Noah's flood.
Darwin's familiarity with human-caused extinction is also clear from On the Origin of Species. In one of the many passages in which he heaps scorn on the catastrophists, he observes that animals inevitably become rare before they become extinct, "we know this has been the progress of events with those animals which have been exterminated, either locally or wholly, through man's agency." It's a brief allusion and in its brevity, suggestive. Darwin assumes that his readers are familiar with such "events" and already habituated to them. He himself seems to find nothing remarkable or troubling about this.
But how, then, to make sense of cases like the great auk or the Charles Island tortoise or, to continue the list, the dodo or the Steller's sea cow? These animals had obviously not been done in by a rival species gradually evolving some competitive advantage. They had all been killed off by the same species, and all quite suddenly—in the case of the great auk and the Charles Island tortoise over the course of Darwin's own lifetime. Either there had to be a separate category for human-caused extinction, in which case people really did deserve their "special status" as a creature outside of nature, or space in the natural order had to be made for cataclysm, in which case, Cuvier— distressingly—was right.
Darwin's successors inherited the "much slow extermination” problem. The uniformitarian view precluded sudden or sweeping change of any kind. But the more that was learned about the fossil record, the more difficult it was to maintain that an entire age spanning tens of millions of years, had somehow or other gone missing. This growing tension led to a series of increasingly tortured explanations. Perhaps there had been some sort of “crisis,” at the close of the Cretaceous but it had to have been a very slow crisis. Maybe the losses at the end of the period did constitute a "mass extinction."
The history of the science of extinction can be told as a series of paradigm shifts. Until the end of the eighteenth century, the very category of extinction didn't exist. The more strange bones were unearthed—mammoths, Megatherium, mosasaurs—the harder naturalists had to squint to fit them into a familiar framework. And squint they did. The giant bones belonged to elephants that had been washed north, or hippos that had wandered west, or whales with malevolent grins. When Cuvier arrived in Paris, he saw that the mastodon's molars could not be fit into the established framework, a "My God" moment that led him to propose a whole new way of seeing them.
"Because of these anthropogenic emissions" Crutzen wrote, the global climate is likely to "depart significantly from natural behavior for many millennia to come."
Crutzen published "Geology of Mankind" in 2002. Soon, the 'Anthropocene" began migrating out into other scientific journals.
Ocean acidification increases the cost of calcification by reducing the number of carbonate ions available to begin with. To extend the construction metaphor, imagine trying to build a house while someone keeps stealing your bricks.
Thousands—perhaps millions—of species have evolved to rely on coral reefs, either directly for protection or food, or indirectly, to prey on those species that come seeking protection or food. This coevolutionary venture has been under way for many geologic epochs. Researchers now believe it won't last out the Anthropocene.
There are various ways to calculate migration rates: for instance, by the number of trees or, alternatively, by their mass. Feeley grouped the trees by genus. Very roughly speaking, he found that global warming was driving the average genus up the mountain at a rate of eight feet per year. But he also found the average masked a surprising range of response. Like cliques of kids at recess, different trees were behaving in wildly different ways.
How many species overall will be capable of moving fast enough remains an open question, though, as Silman pointed out to me, in the coming decades we are probably going to learn the answer, whether we want to or not.
You could be studying a chain of islands or a rainforest or a nearby state park, and you'd find that the number of species varies according to the same insistent equation: S = cA squared.
Smaller areas harbor smaller populations, and smaller populations are more vulnerable to chance. To use an extreme example, an island might be home to a single breeding pair of birds of species X. One year, the pair's nest is blown out of a tree in a hurricane. The following year, all the chicks turn out to be males, and the year after that, the nest is raided by a snake. Species X is now headed toward local extinction. If the island is home to two breeding pairs, the odds that both will suffer such a string of fatal bad luck is lower, and if it's home to twenty pairs, it's a great deal lower. But low odds in the long run can still be deadly.
I thought about this as we trudged back to camp. If Cohn-Haft was right, then in its crazy, circus-like complexity the ant-bird-butterfly parade was actually a figure for the Amazon's stability. Only in a place where the rules of the game remain fixed is there time for butterflies to evolve to feed on the shit of birds that evolved to follow ants.
Long-term relationships between pathogens and their hosts are often characterized in military terms; the two are locked in an "evolutionary arms race," in which, to survive, each must prevent the other from getting too far ahead. When an entirely new pathogen shows up it's like bringing a gun to a knife fight. Never having encountered the fungus (or virus or bacterium) before, the new host has no defenses against it.
If we look even farther ahead than Elton did—millions of years farther—the biological world will, in all likelihood, become more complex again. Assuming that eventually travel and global commerce cease, the New Pangaea will, figuratively speaking, begin to break up. The continents will again separate, and islands will be re-isolated. And as this happens, new species will evolve and radiate from the invasives that have been dispersed around the world. Hawaii perhaps will get giant rats and Australia giant bunnies.
If, on the other hand, people were to blame—and it seems increasingly likely that they were—then the import is almost more disturbing. It would mean that the current extinction event began all the way back in the middle of the last ice age. It would mean that man was a killer—to use the term of art an "overkiller"—pretty much right from the start.
It’s only fully modern humans who start this thing of venturing out on the ocean where you don't see land. Part of that is technology, of course; you have to have ships to do it. But there is also, I like to think or say, some madness there. You know? How many people must have sailed out and vanished on the Pacific before you found Easter Island? I mean, it's ridiculous. And why do you do that? Is it for the glory? For immortality? For curiosity? And now we go to Mars. We never stop.
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 the woolly rhinos. With the capacity to represent the world in signs and symbols comes the capacity to change it, which, as it happens is also the capacity to destroy it.
Certainly humans can be destructive and shortsighted; they can also be forward-thinking and altruistic. Time and time again, people have demonstrated that … they’re willing to make sacrifices on those creatures’ behalf.
Among the many lessons that emerge from the geologic record, perhaps the most sobering is that in life, as in mutual funds, past performance is no guarantee of future results.
