The Sixth Extinction: Chapter 10 Summary & Analysis

In 2007, a team of biologists decided to count the number of bats in Albany, New York. In the dead of winter, they climbed into caves with the expectation of seeing bats in hibernation. What they found was shocking: thousands of bats, seemingly lying dead on the ground, covered in a strange, powdery white substance. The next year, the scientists investigated the caves and again found freshly dead bats, covered in the same white substance. The bat die-off continued for years and spread to other states. Eventually, scientists learned that the white powder was a cold-loving fungus, Geomyces destructans, that is deadly to bats.

Darwin’s ideas are helpful to understanding the significance of the bat die-off. Darwin argued that, for all intents and purposes, most animals cannot travel long distances. The idea of natural selection assumes the existence of isolated environments with natural barriers like mountains, oceans, rivers, etc. Thus, it’s possible to speak of the Galápagos Islands or the western Caribbean as separate “units,” each with its own unique life. The problem with Darwin’s assumption, of course, is that many animals are capable of traveling long distances over natural barriers. And in the Anthropocene, animals are dispersed around the world, thanks to the actions of human beings. Humans travel to every different continent and they move animals, plants, and microbes with them—an event that is utterly unprecedented in planetary history.

Kolbert, who lives near the Albany bat caves, discovered that the lethal fungus had spread as far as West Virginia. She met with Al Hicks, one of the scientists who had discovered the dead bats in Albany. Hicks took Kolbert into the Adirondacks, the mountains where his team was conducting environmental tests. Hicks counted brown bats (Myotis lucifugus) and other endangered bat species. Many bats had the telltale white fungus growing on their bodies.

In the Anthropocene, species move around the world in a process similar to Russian roulette. When a species encounters a new environment, two things can happen: 1) nothing; 2) the new environment kills the species. Most of the time, a species can’t adapt to a new environment. But when a species does so, it reproduces and may sometimes spread to other surrounding environments. It’s not clear why some species are better at adapting and proliferating than others—perhaps their success is as random as Russian roulette. However, scientists have hypothesized that when a species moves to a new environment it often has fewer evolutionary rivals and predators, and therefore its population explodes.

When a species is introduced to a new environment, the species sometimes wipes out the diversity of life in that environment. For instance, humans brought the brown tree snake to Guam from Australia in the 1940s; within a few years, a huge chunk of Guam’s bird species were extinct, eaten by the brown tree snake. New pathogens (viruses, bacteria, fungi, etc.) are particularly quick to spread; introducing a fungus to a new environment often leads to the near-extinction of other life forms. To give one example, the sudden appearance of a Japanese fungus in the U.S. in the early 20th century virtually wiped out the country’s chestnut population. The white fungus that killed off bats in Albany is also an example of how dangerous a new pathogen can be.

Chances are, wherever you are on Earth, you can see a couple of species that humans have introduced to the environment. There are vast databases of “invasive species”—species that have been introduced to a new environment and have harmed the environment’s biodiversity. In Brisbane, Australia, for example, the cane toad, introduced in the early 20th century, has wiped out hundreds of plant and insect species. In a way, the phenomenon of global species travel is “turning back the clock” to the prehistoric time when the Earth’s landmass was one huge supercontinent, Pangaea. In the “New Pangaea,” there are, in effect, no natural barriers anymore—species can move anywhere in the world, thanks to human beings.

Kolbert and Hicks travel to the famous Aeolus Cave in Vermont, the home of one of the largest bat caves in America. As they enter the cave, they notice a huge pile of dead bats, some freshly dead, some badly decomposed. Hicks and his team proceed to put the dead bats in plastic bags so that they can be tested in a lab later on.

When did the “New Pangaea” come into existence? Humans have used their ingenuity to cross natural barriers for many thousands of years, but particularly in the post-Columbian era, when nautical travel has become more common, the rate of species exchange has increased enormously. One group estimates that California alone acquires a new invasive species every sixty days. The short-term impact of species invasion is more diversity, since there is, literally, one extra species in the ecosystem. But in the long-term, biodiversity decreases as a result of the invasive species’ dominance.

The study of invasive species arguably began with the work of Charles Elton in the 1950s. Elton compared the movement of species to the exchange of gases in a set of tanks. If closed-off tanks of different gases were suddenly allowed to intermingle, the previously isolated gases would combine into new chemicals. In the short-term, there would be a lot of molecular movement. Eventually, however, the gases would reach a new equilibrium, in which there was less molecular variety. Following Elton’s analogy, it seems that, in the future, the New Pangaea will reach a new equilibrium, but this new equilibrium will probably host fewer species than exist on Earth now. Perhaps many millions of years from now, if human commerce ceases, biodiversity will begin to grow again.

Kolbert returns to the Aeolus Cave the next year, with a team of biologists from the Vermont Fish and Wildlife Department. The team counts only 112 bats—less than 10% of the norm. Geomyces destructans has thrived in New England because bats are highly sociable creatures; they spread the white fungus to other bats quickly. Meanwhile, the brown bat, and a few other bat species, has become endangered.