The Sixth Extinction: An Unnatural History (2014)

In Chapter One, Kolbert introduces the readers to the golden frog of central Panama, an amphibian once so ubiquitous that it became a lucky symbol in Panama and could be found decorating everything from skirts to taxicabs to lottery tickets. Within the last decade, the frogs were easy to see in the hills of El Valle de Anton. Their bright yellow color signaled their toxicity, as “the poison contained in the skin of just one animal could kill a thousand average-sized mice” (4).

Then, to the west of Panama, the frogs began to disappear abruptly. The mysterious disappearance was first noted by an American graduate student who, when returning to Panama to complete her studies, could no longer find any of the frogs for observation. When she set up her research further to the east, she saw plenty of healthy frogs, for a time. Then they, too, began to die off. Suddenly, scientists realized they had a crisis on their hands as a blight spread through the region, effectively killing off the frogs. In desperation, scientists captured some frogs to keep them in a safe, secure location, out of the reach of the disease.

At this time, Kolbert read an article about this phenomenon wherein the authors claimed that the frogs’ destruction could be a sign of a Sixth Extinction. Intrigued, but somewhat skeptical, Kolbert decided to travel to Panama to see the situation for herself. After all, she rationalized that if the authors were correct, then “those of us alive today not only are witnessing one of the rarest events in life’s history, we are also causing it” (8).

In Panama, Kolbert meets the El Valle Amphibian Conservation Center’s director, Edgardo Griffith, who has dedicated significant time and effort to preserving as many amphibians as possible. To Griffith, “Every one of them has the same value … as an elephant” (9). He laments the loss of amphibian species, especially those species that have been utterly unknown to scientists. He notes that even the average citizens of El Valle ask him where the frogs have gone, as they can no longer locate them.

Kolbert notes that amphibians are “among the planet’s great survivors” (10), having survived for eons and having existed on the planet long before dinosaurs walked the earth. This incredible class of life has continued to live through massive upheavals, including being uprooted from its natural environments. Amphibians can now be found everywhere in the world except for Antarctica.

The most mysterious aspect of the vanishing frog species has to do with their geographical distribution. Frog species began disappearing from both populated areas and preserved rural places. Additionally, the species began to disappear at roughly the same time from multiple parts of the world. One culprit responsible for the frogs’ deaths was discovered to be a chytrid fungi that prevented frogs from absorbing electrolytes through their skin, effectively causing a heart attack.

Unfortunately, as the scientists at the conservation center have found, the chytrid fungi do not need amphibians to survive. Thus, if the frogs currently housed in secure locations within the center are released back into their natural environments, they will still be exposed to the fungi, sicken, and die. Griffith notes that “The point is to be able to take them back, which every day I see as more like a fantasy” (14). Worse yet, the chytrid has spread worldwide and appears to be unstoppable.

In the previous Five Extinctions, which Kolbert calls “panics,” the dominant organisms, like the amphibians, disappear or take on lesser roles, causing the “usual rules of survival [to be] suspended” (16). Today, however, amphibians are no longer alone in being an endangered class of animals. They are joined by coral reefs, sharks and rays, mollusks, birds, and reptiles, and species are being lost all over the world.

Human beings are partially to blame: as Kolbert explains, the chytrid fungi would not have been able to spread worldwide if it had not been transported by plane or boat. Indeed, this “intercontinental reshuffling, which nowadays we find totally unremarkable, is probably unprecedented in the three-and-a-half-billion-year history of life” (18).

Accompanying Griffith on an expedition to test some frogs and bring back new species to the center, Kolbert realizes that these frogs, their offspring, and their offspring’s offspring “will never again touch the floor of the rainforest but would live out their days in disinfected glass tanks” (21).

Kolbert introduces the concept of extinction and explains how modern humans, taught the idea in general through stories and toys of dinosaurs, grow up accepting that it exists. This was not always true throughout human history. Great philosophers, thinkers, and scientists like Aristotle, Pliny, Pope, and Linnaeus didn’t even consider extinction as a possibility. Despite fossil evidence to the contrary, extinction was not accepted as a concept until the days of revolutionary France.

The focus of this chapter is naturalist Jean Leopold Nicolas Frederic Cuvier, a scientist who was ahead of his time and had an “essentially tragic vision of earth history [that] has come to seem prophetic” (24). Cuvier came to North America from France to weigh in on the mystery surrounding giant bones found along the Ohio River in what is now Kentucky.

The first European-American discovery of American mastodon bones came at the hands of Charles le Moyne when he was leading his troops down the Ohio River in 1739. After setting up camp along the river one day, le Moyne’s troop came upon a smelly marsh that contained “hundreds—perhaps thousands—of huge bones … like spars of a ruined ship” (25). After the humiliating defeat of his troops by the Chickasaw, le Moyne shipped the bones—a tusk, teeth, and giant femur—to France as a gift for King Louis XV.

The king promptly put the bones on display, and arguments began as to what kind of creature these bones belonged. The tusk and femur looked like an elephant’s or a mammoth’s, but the teeth did not. This creature’s teeth were unlike mastodon teeth, which are cusped, and entirely unlike elephant’s teeth, which are flat on top. These differences led to many theories, some sensible and some wild, as to the creature’s origins, with one physician, William Hunter, noting that the teeth appeared to have belonged to a carnivorous animal.

Even Thomas Jefferson was caught up in the mystery, dispatching Meriwether Lewis and William Clark on a Northwestern expedition in hopes that they would find live specimens of this unknown American animal.

Then Cuvier came onto the field. His primary job was to teach at the Natural Museum of History in Paris, but when he wasn’t in class, he spent his time in the museum’s collections. Cuvier spent many hours studying the bones sent by le Moyne from America, and in 1796, he gave a public lecture about his findings. In his speech, he discussed how different species of elephants, specifically elephants from the Ceylon and the Cape of Good Hope in Africa, had significant differences in tooth structure. Therefore, Cuvier believed that the bones of the mysterious American monster belonged to a lost species. He argued that there were at least four extinct species of these elephant-like creatures around the globe.

In presenting his theory, Cuvier “had conceived of a whole new way of looking at life” (29)—that is, that species could become extinct. For Cuvier, this conclusion prompted questions such as what the primitive earth was like, and what could have caused its species to be entirely eradicated.

In this chapter, Kolbert meets with Pascal Tassy, the director of the Natural Museum of History, who takes her to the teeth in question, the very ones that Cuvier had studied and drawn. She notes how incredible it was that Cuvier hit upon the right idea behind the bones, considering his lack of evolutionary experience and study.

To support his theory that there must be evidence of other extinct species from earlier epochs on Earth, Cuvier set out to find some of them. He received extensive assistance from people all over Europe who enthusiastically shared their finds with him. By 1800, Curvier had amassed a “fossil zoo” (33), full of the bones of at least twenty-three suspected extinct species. To prove some of his hypotheses, Cuvier would indulge audiences in a public test where he would prove that one set of bones belonged to a marsupial or giant amphibian. Then, Cuvier received an engraving of a strange fossil found in Bavaria of a beaked creature with long arms and fingers. He determined, based on the engraving, that the animal was “a flying reptile. He called it a ptero-dactyle, meaning “wing-fingered” (35).

Cuvier’s findings created a sensation around the world, putting ancient bones in high demand. One example provided by Kolbert is that of an American mastodon found in Newburgh, New York in the late 18th century. The skeleton was put on public display, causing “mammoth fever” (36), with towns creating mammoth-themed foods and products to capitalize on the mayhem surrounding the animal’s fame. It was Cuvier who gave the creature its scientific name, mastodonte, and his reputation only grew as the naturalist garnered more bones and skeletons for his study. The enthusiasm stoked by Cuvier’s work produced a whole new career field, that of “fossilists.” Fossil-hunters began finding the bones of bizarre-looking animals, including parts of what would eventually be recognized as dinosaurs, within the decade.

Originally, Cuvier argued that animal extinctions had happened because of “some kind of catastrophe” (42), but he changed his position after further study to the theory that there had been multiple disastrous events on Earth and that “[l]iving organisms without number [had] been the victims of these catastrophes” (43). He did not believe that smaller disturbances, such as volcanic eruptions or forest fires, were enough to wipe out a whole species. In Cuvier’s opinion, “the changes that had caused extinctions must therefore have been of a much greater magnitude—so great that animals had been unable to cope with them” (44).

Cuvier, citing changes in rock formations and referencing ancient texts and myths, wrote a major essay about his cataclysmic stance. Although the empirical grounds of Cuvier’s theory have since been disproved, many of his original claims turned out to have been entirely accurate. In fact, his belief that the American mastodon had been killed off thousands of years ago was correct, and the reason for its extinction was indeed a cataclysm: the spread of human beings. 

Kolbert begins Chapter Three by addressing the term “catastrophist,” coined by William Whewell, president of the Geological Society of London in 1832. Whewell’s position that a catastrophe was indeed causing environmental change was disregarded by a young geologist named Charles Lyell. A friend of Cuvier’s, Lyell often dined with the naturalist, making casts of many of Cuvier’s most famous fossils. Although he was friends with Cuvier, Lyell dismissed Cuvier’s theories of cataclysms and extinctions. Lyell thought that, at any time, a species that might have appeared to be gone for good could reappear again.

Lyell published his work, called Principles of Geology, in three volumes, and it became a commercial success. One twenty-two-year-old graduate named Charles Darwin was given a copy of the first volume to take with him on the four-year sea voyage where he would first garner ideas for his scientific theory. He was so intrigued by what he read that he had the second and third volumes shipped to him at different points in his journey.

While traveling along the South American coast, Darwin experienced an earthquake and described the ensuing rubble and destruction as a “most awful yet interesting spectacle” (51). Using surveying measurements, Darwin found that the harbor in Concepcion had been elevated eight feet due to a series of earthquakes, thus reinforcing Lyell’s theory. Darwin also saw the coral reefs and began to see that “the key to understanding coral reefs was the interplay between biology and geology” (52). Upon returning to England, Darwin presented Lyell with his findings, which thoroughly delighted Lyell.

Like Cuvier, Lyell was much more interested in extinct species than in understanding how new species developed. Darwin, however, with his theory of natural selection, recognized that just as the inorganic world could change over time, “the organic world similarly was subject to constant flux” (53). Lyell disagreed with Darwin’s position, and this disagreement ended their friendship. In truth, Darwin’s theory provided reasoning for both the extinction of species and the emergence of new species. Kolbert points out that although Darwin believed that extinction happened at such a slow rate as to be unnoticeable, during his own lifetime, the extinction of the great auk proved him wrong.

To flesh out this story, Kolbert travels to the Icelandic Institute of Natural History in Reykjavik to see its great auk, as the museum has one of the last specimens, killed in 1821. The deputy director, Gudmundur Gudmundsson, takes Kolbert to where the auk is preserved, “perched on a fake rock, next to a fake egg” (56). The auk was a large, flightless bird of the Northern Hemisphere with tiny wings and a “large, intricately grooved beak” (57). In its prime, the great auk numbered in the millions, and its population only began to decline with the advent of human settlers who regularly used the bird as a food source. Kolbert argues that the great auk lived a life similar to that of penguins, and that great auks were “the original ‘penguins’” (57). This was the term that sailors gave to the flightless birds; the term was used to name a variety of flightless birds, even though penguins and auks are from completely different families.

Like penguins, the great auks were exceptional swimmers, but they needed to come ashore during the summer months to breed, making them vulnerable to hunters. With the advent of Europeans’ voyages to Newfoundland, the great auk’s existence was endangered. Over a period of decades, the great auks were used for much more than meat: they were used as fuel and fish bait, and their feathers were used in mattresses. The methods by which they were killed—plucked or burned alive—were heartless and inhumane. By the 1700s, the great auk population was in severe decline, and by 1844, the bird was gone from North America.

The great auks’ last refuge was in Iceland, on an island called Eldey, but it was a temporary haven. The rarity of the great auk had made it a valued prized amongst hunters who wanted to add to their collections. In 1844, the last pair of auks was killed for this purpose.

Kolbert arranges transportation out to Eldey to see where the great auks once lived. She recounts how Alfred Newton, future Cambridge professor of zoology, had traveled to Eldey and determined that the great auk was indeed extinct, and how it caused him to consider the future of other birds, specifically those that lived and bred along the British coast. Newton realized that birds were being hunted in exorbitant numbers, and that the hunting birds could lead to extinctions like that of the great auks.

Due to Newton arguing for a hunting ban during breeding seasons, the first wildlife protection law, the Act for the Preservation of Sea Birds, was enacted in 1869. Newton became associates with Darwin, and both men discovered they had similar positions regarding the extinction of species. Darwin had good reason to believe in human-caused extinction as he had witnessed it to some extent during his trip to the Galapagos. This meant that naturalists like Darwin and Newton had to identify a specialized category of extinction for those cases where species had been killed off quite suddenly by human beings.