The Sixth Extinction: Chapter 2 Summary & Analysis

Extinction is one of the first scientific concepts that children learn about; when small children play with toy dinosaurs they learn that the dinosaurs died a long time ago. Strange as it sounds, a small child living in the 21st century has a better grasp of the history of life on Earth than scientists did thousands of years ago. Aristotle, for instance, wrote a long treatise on animals without considering the possibility that some animals went extinct. In the mid-18th century, when the great biologist Carl Linnaeus began taxonomizing the animal kingdom, he didn’t address the possibility that some animals had died out long ago. Even today, there are some people who believe that no animals have ever gone extinct—or that the animals that went “extinct” drowned in the great flood described in the Biblical Book of Genesis.

Scientists first proposed the concept of extinction in the late 18th century. A naturalist named Georges Cuvier studied the fossils of an animal now known as the American mastodon, or Mammut americanum, and concluded that all such creatures must have died out in the distant past. In his own lifetime, many of Cuvier’s own ideas about extinction were harshly criticized—but now, hundreds of years later, Cuvier is praised for being ahead of his time.

European explorers probably discovered mastodon teeth in the early 18th century; then, in 1739, Charles le Moyne, the Baron de Longueuil, discovered mastodon bones while exploring present-day Ohio. His men carried the bones back to New Orleans, where they were shipped back to King Louis XV in France. Louis kept the mastodon bones in his museum.

For most of the 18th century, French scientists debated the origins of the mastodon remains. Some argued that the bones actually belonged to two or three creatures, including a hippopotamus. Other scientists proposed that the bones belonged to an entirely new animal—the “American elephant.” Georges-Louis, Leclerc, Comte de Buffon, France’s most famous naturalist, proposed that the remains belonged two three animals—an elephant, a hippopotamus, and a new species, which had disappeared a long time ago. Even Thomas Jefferson, a naturalist as well as a statesman, wrote a paper in which he argued that the remains must belong to an existent, undiscovered animal, probably the largest animal alive. Jefferson hoped to track down this mysterious animal somewhere in the American continent.

Cuvier lived in Paris at the end of the 18th century, and worked as a lecturer for the Paris Museum of Natural History. On April 4, 1796, Cuvier delivered a revolutionary lecture in which he discussed the Mastodon remains from Ohio, as well as the remains of a similar creature that had been discovered in Russia. Cuvier proposed that the two sets of remains belonged to huge, elephantine creatures—two new animal species, neither one of which had survived. Cuvier called these kinds of creatures “espèces perdues,” or “lost creatures.” Cuvier based his theory of lost creatures on his own research into the Ohio and Russia fossils, as well as animal remains from Argentina. Finding evidence of other lost creatures among those remains, Cuvier concluded that they must have belonged to vanished species. He extrapolated these findings to conclude that there must be a huge number of species that died out over time. Cuvier did not, however, understand what could have led these lost species to die out.

Kolbert meets with Pascal Tassy, the current director of the Paris Museum of Natural History. Tassy shows Kolbert the museum’s vast collection of elephant, mammoth, and mastodon remains, including the mastodon teeth that Longueuil found in Ohio. Mastodon teeth are huge and brownish, but they have the same basic structure as human teeth; dentin, surrounded by brittle enamel. Tassy also shows Kolbert the “Maastricht animal,” a famous fossil that Cuvier identified, correctly, as belonging to an extinct marine reptile (now known as the mosasaur).

Cuvier’s lectures at the Museum popularized the theory of extinction. However, Cuvier needed to find more fossils to bolster his claim that the Earth was once full of now-extinct species. Cuvier investigated the quarries surrounding Paris, eventually identifying twenty-three new species that he believed to be extinct. Cuvier traveled around Europe, exhibiting his fossils with a showman’s theatricality. One of Cuvier’s most famous discoveries was the pterodactyl, which he correctly identified as an extinct flying reptile.

The theory of extinction was particularly popular in the early United States, owing partly to the influence of Thomas Jefferson. Jefferson’s close friend, Charles Willson Peale, established a natural history museum in Philadelphia, where he displayed many notable fossils discovered in North America. Peale arranged for fossils to be reconstructed at the museum—one of these, an American mastodon, was dubbed a “mammoth” because of its size. The popularity of the so-called “mammoth” (technically, a mastodon) sparked a national vogue of foods and taverns named after the creature. In 1806, Cuvier published a paper in which he officially named the creature a “mastodon”—however, the name “mammoth” had caught on by that time, creating a lasting confusion between the two terms. Later, scientists discovered another extinct, elephantine creature, and named it the “mammoth,” further increasing the confusion.

Toward the end of his life Cuvier became a hero throughout Europe and the U.S.—scientists accepted his theory of extinction, and wealthy aristocrats took up “fossil hunting” as a hobby. One fossil hunter discovered the remains of a huge, lizard-like creature, the ichthyosaur. Slowly, scientists began to notice a pattern with fossils—the older the fossil, the deeper in the earth it was likely buried (fossils discovered near the surface likely belonged to non-extinct animals).

Strangely, Cuvier’s theories of extinction blinded him to the existence of biological evolution. He noticed that animals’ bodies were perfectly calibrated to their diet and habitat—for example, horses have hooves, rather than claws, since they are herbivores that don’t need to hunt other animals for food. Based on his observations, Cuvier concluded that it was impossible for animals to mutate or evolve over time, since even the tiniest changes in an animal’s body would prevent it from surviving. Cuvier’s great rival was his colleague at the Museum of Natural History, Jean-Baptise Lamarck. Lamarck proposed that animals could slowly change their own bodies over time—for example, he argued that giraffe’s necks were long because giraffes had spent millennia reaching for leaves in tall trees. Cuvier ridiculed Lamarck’s theories, citing the remains of ancient Egyptian cats as proof that animals today are no different from animals thousands of years ago.

Cuvier had determined that some species went extinct over time. But he still needed an explanation for why this happened. At first, he proposed that one great disaster in the distant past had wiped out species simultaneously. Later, after fossil hunters had identified distinct “layers” of fossils, he changed his mind and argued that there had been multiple cataclysmic events that led to multiple extinctions. In 1812, Cuvier wrote an influential essay about the possibility of ancient, cataclysmic events. Although Cuvier made a point to cite multiple religious texts in his essay, the predominately Anglican staff of Oxford and Cambridge ensured that, when the essay was translated into English, it favored a Christian interpretation. In this way, Cuvier’s research was used to “prove” the existence of Noah’s flood.

Many of Cuvier’s ideas have been debunked, wholly or partially—for example, he believed that there was a mass-extinction just before the beginning of recorded history, which is untrue. However, his basic idea that species go extinct over time paved the way for future research. Interestingly, Cuvier pointed out that the American mastodon went extinct about 13,000 years ago, which is correct. However, though he thought this was due to floods or other large natural disasters, the mastodon probably went extinct because human beings hunted it to extinction.