The Sixth Extinction: An Unnatural History
That dinosaurs have permeated mainstream culture in the 21st century is confirmed by their presence in internet memes, such as ‘Whenever you’re sad imagine a T-rex making a bed ’ or the ‘Philosoraptor ’. What began in picture books replete with enormous, elegant creatures alongside lush jungle foliage and beautiful waterfalls has now grown up with the generation that read them. Consequently, extinction has become just another fact we encounter as an abrupt end to the narrative, and our bedtime stories. It is easy to forget that this unimaginably horrible cataclysmic event happened on our planet and wiped out innumerable distinct species. In what amounted to an instant in the earth’s history, the composition of life was irreversibly altered. In her book The Sixth Extinction, Elizabeth Kolbert questions whether humans today are having a similarly catastrophic impact on the biodiversity of the planet. As she put it in a recent interview with National Geographic, “We are the asteroid now.”
Kolbert’s book takes this issue away from dinosaurs and into our day and age, tackling the idea of extinction, from its relationship to evolutionary theory and acceptance by the scientific community, to the various triggers that can cause a species to disappear. In order to complete her project, Kolbert, a scientific layperson, makes a series of trips around the world in order to assemble the widespread drivers of extinction. From recording a bat census in New England mines to collecting water samples on a coral graveyard off the Great Barrier Reef, she tries her hand at fieldwork while learning how science approaches questions of extinction, past and present. In the narrating of her adventures, Kolbert’s journalistic pedigree and casual prose are both a blessing and a curse. The dialogue is, at times, weighed down with superfluous personal information and unnecessary anecdotes that add comedy at the expense of making scientists and their work seem laughable. This intimate writing style, however, allows the reader to encounter an honest view of the challenge of daily life in small remote scientific outposts. Kolbert manages to capture the enthusiasm and tenacity of scientists as they pursue a better understanding of our planet, from collecting daily water samples to embarking on twilight frog-napping excursions in the rainforest. Although her contrasts are occasionally clumsy, the juxtaposition of these stories with weighty scientific issues enables us to see how the aggregation of many seemingly trivial studies can address complicated questions and expand our knowledge.
Kolbert begins her book with the surprising fact that before Jean-Léopold-Nicholas-Frédéric Cuvier, the French natural historian, first proposed the idea that some osteological remains came from animals no longer in existence in 1796, we had no idea of the extinction of species. Cuvier’s proof of his revolutionary theory of espéces perdues came from the examination of teeth—specifically those of elephants, American mastodons, and Siberian mammoths. Fossil collecting suddenly became a hobby of the upper class. From his findings, Cuvier advanced the theory of catastrophism, according to which extinctions were caused by cataclysmic events that wiped out many species at one time. Catastrophism remained the dominant way of understanding extinction until, in 1830, Charles Lyell, an Oxford lawyer-turned-geologist, popularised the uniformitarian theory of geology in 1830, which asserts that extinction is a consistent and uniform process. Thus when Darwin published his On the Origin of Species in 1859, the question of how extinction happened was entangled in the concept of evolution. It was not until the discovery of the meteorite crash that ended the Cretaceous period in 1978 that scientists were able to arrive at a consensus that both Cuvier and Lyell were partly correct in their theories of extinction.
Climate change, globalization, and land development are altering ecosystems across the globe at rates much greater than evolutionary processes. Some argue this marks a catastrophic extinction event. These changes are creating paradoxical situations for many species. Increasing temperatures and shifts in rain patterns are forcing species to migrate to stay within habitable environments. Miles Silman, a scientist working high up in the Andes, has even shown that trees are moving: as the average temperature of South America increases, the average positions of some tree species are gradually heading up the mountain. But what happens if creatures cannot move? Cities become sprawling roadblocks, while agricultural land creates pockets of isolated wilderness. On top of these challenges, the movement of people and goods across the world spreads invasive stowaways and disease. If invasive species find their new environment amenable, native plants and animals become susceptible to new diseases, must compete for resources, and may face new predators against which they cannot defend themselves. As people continue to travel globally, they are homogenising the flora and fauna of the planet.
Our alteration of the atmosphere and land is only part of the human-planet relationship. Ocean acidification, climate change’s “equally evil twin”, is already having major effects on life in the seas. The oceans act as a sink of carbon dioxide. Therefore, burning fossil fuels and other anthropogenic carbon emissions increase the level of dissolved carbon dioxide. A significant fraction of the dissolved gas becomes carbonic acid, which decreases the pH of the water. Many creatures, especially corals, are highly sensitive to the acidity of their environment. These small creatures leave behind hard calcium-based exostructures that create colourful intricate reefs, but calcium degrades in the presence of acid. In fact, the plight of corals reefs—which are home to a myriad of other species—is so dire scientists predict that in fifty years coral growth will effectively cease. Our great-grandchildren may only ever see coral in textbooks. While the impact of changes to atmospheric chemistry and thermodynamics is still up in the air, scientists can confidently predict, with increasing certainty, what future oceans will look like. Currently, the media’s symbol of climate change is a melancholic polar bear stranded on a fragment of melting ice, but perhaps a more powerful warning of the effects of carbon emissions would be images of the vivacious coral reefs that have been reduced to dead rubble.
Humans have the rather dubious honour of being responsible for the birth of a new geologic epoch, the Anthropocene. The large changes to the land beginning in the Industrial Revolution, by fossil fuel emissions, alterations of waterways, and urban or agricultural development, will leave an indelible mark in the geological history of the planet. Kolbert points out that mankind’s impacts extend beyond the Anthropocene and examines the role Homo sapiens have historically played in nature. Throughout our existence, we have been skilled hunters. The demise of large animals followed the emergence of humans from Africa as they spread through Europe, Asia, and eventually the Americas. Humans were a new type of predator. They could create weapons, work in groups to overcome creatures much larger than themselves, and—most importantly—wandered extensively as a species. In Kolbert’s words, “before humans emerged on the scene, being large and slow to reproduce was a highly successful strategy, and outsized creatures dominated the planet. Then, in what amounts to a geologic instant, this strategy became a loser’s game.” When humans encountered Neanderthals and other similar species, we reproduced with them—and then wiped them out. Even to this day, 1-4% of the genetic make-up of non-Africans can be traced back to our sister species. This brings our current behaviour in modern times into a different light. Humans have left a trail of extinctions in their wake, in their existence as a species; it is merely the rate and extent of the impact that has recently changed.
Overall, Kolbert treats the heavy issues of anthropogenic impacts on the environment with a refreshingly neutral tone. While other popular science books often appear to condemn human behaviour and seek to proselytize, Kolbert does not pass judgment on our actions. The book serves as a powerful and effective warning not because of doomsday hyperbole, but rather because of the scientifically valid theories posited by scientists working in the field. Kolbert does not offer any idealistic solutions—many of the changes discussed in the book are happening now and will continue regardless of major shifts in policy or lifestyle in the next few decades. However, she is correct to address the vital importance of ensuring the public are aware of the effects we are having: “to argue that the current extinction event could be averted if people cared more and were willing to make more sacrifices is not wrong, exactly; still, it misses the point. It doesn’t matter whether people care or don’t care. What matters is that people change the world.”
The last chapter in the book offers a bittersweet message of hope. Homo sapiens have always been a disruptive interloper in any environment they encounter. But now we are finally recognizing the responsibility imbued by our unique position in the hierarchy of nature and actively using our resources to preserve and protect endangered species. Humans may be responsible for wreaking havoc on the balance of nature, but we are also the only species who can expend enormous resources to save others.
In looking to the future earth, we must examine our past. How many species will be reduced to cartoons in stories because of our actions? Are we doomed to be the meteorite that destroys life? Or can humans learn to become responsible citizens of our planet and respect our role in the intricate web of life? As the title suggests, humans are an incredibly destructive force, one that has already extinguished innumerable species, with many others destined to follow. Kolbert offers compelling evidence that the rate and extent of the carnage is only increasing, which underscores the acute importance of scientific research in fields like geology and zoology. We can only hope to find solutions to preserve the magical diversity and beauty of our planetary home if we first understand our impact on the planet’s intricate ecosystems.
Katherine Manfred  is reading for a DPhil in Chemistry at Magdalen College, Oxford.