The Sixth Extinction: An Unnatural History by Elizabeth Kolbert

The Sixth Extinction by Elizabeth KolbertBacon Phat
00:00 / 1:13:42

The Sixth Extinction takes an investigative journalism approach to covering the real-time extinctions of several species throughout the world as a way to show the scope of a serious man-made problem—a problem that began with the arrival of the first humans and has continued, though for different reasons, today.

In this episode, we discuss:

Show notes:

The Sixth Mass Extinction

Prior to our current extinction, the planet experienced five mass extinctions, according to scientists. Kolbert offers several scientists’ descriptions of mass extinctions to communicate that message that they are really catastrophic. Under normal conditions, about one species should go extinct every 700 years. In a mass extinction, species go extinct left and right, seemingly without cause. According to Kolbert, the previous five mass extinctions happened at the end of the Ordovician period, in the late Devonian, at end of the Permian, in the late Triassic, and at the end of the Cretaceous.


Humans are responsible for several aspects of the planet’s sixth mass extinction, which began some 200,000 years ago. This argument is relatively new. In fact, until the 1800s scientists did not even agree that species could go exist, let alone that a mass extinction was taking place. Kolbert outlines the history of the study of extinction and its theories, beginning with the discoveries of strange bones belonging to unknown monsters.

Humans did not always believe in extinction


Charles Darwin, celebrated champion of the theory of evolution, did not believe in mass extinction. He believed species gradually declined, the process for a species’s end happening much slower than its beginning. And the sudden disappearance from the fossil record denoted a loss of fossils, not a mass extinction. Darwin’s predecessor, Jean Baptiste Lamarck, did not believe that species went extinct; he believed they simply transformed into other species. If a fish suddenly needed to develop feet for some reason, it would develop them and the regular fish would cease to be what it had been—but it would not be extinct. This idea was known as transformisme. And then there was George Cuvier, who didn’t believe in evolution like Darwin or transformisme like Lamarck but did believe in mass extinction. He believed major catastrophic floods wiped out large amounts of species at a single time, using geology as evidence of the theory.


Ocean acidification is a hidden cause of extinction

One of the methods by which humans contribute to mass extinction is through manmade carbon emissions. Increased carbon in the atmosphere means increased hydrogen ions in the ocean, which means a lower pH (i.e. ocean acidification) and an decrease in available carbonate ions to make calcium carbonate shells. Also affected are coral reefs. They and other calcium carbonate-dependent organisms will start to dissolve if the aragonite saturation state falls below 1. While this has not happened yet, the drop in saturation observed since the Industrial Revolution has been the greatest in the last 300 million years.

Most of the world's amphibians are going extinct


More than 50% of the world’s amphibians are facing extinction. All of a sudden, in the 1970s, frogs all over the world began dying in alarming numbers. Scientists eventually discovered that the chytrid fungus was the culprit, and scientists believe it is very possible that humans have helped spread it. One of the stupider ways humans have spread the fungus around the world is by harvesting the South African clawed frog for use in human pregnancy tests. Pee from a pregnant woman injected into the bladder of the clawed frog will force the frog to lay eggs within a few hours. This type of exploitation of a species (and the ramifications it has for the extinction of countless other frog species) shows the height of human selfishness, hubris, and cruelty.


To learn more about the amphibians’ mass extinction, Kolbert travels to Costa Rica to visit El Valle Amphibian Conservation Center (EVACC). The team travels into the rainforest to collect frogs for study at EVACC. While the team resists the temptation to take every frog it sees, it brings in a few frogs that are some of the last of their species. And Kolbert writes a chilling line to the effect of, “I realized they will never see the forest floor again.” Essentially, humans, largely responsible for the destruction of these frog species in the first place, are gathering up the last ones left and putting them in small glass boxes for the remainders of their short lives. Humans can tell themselves that sequestering the frogs is ultimately for the frogs’ benefit, but it seems to serve humans’ curiosity and assuage their guilt more than anything.

Millions of bats around the world have died

Similarly, bat species throughout North America are plagued by white nose syndrome, also due to a fungus. As of 2018, millions of bats have died, and in some places, bats have been 100% eradicated. The fungus colonizes the bat’s skin, disrupting its hibernation and making it active during the day when it should be asleep. It appears that some species throughout North America are more affected by it than others, and while the fungus has been found on bats in Europe and Asia, those bats don’t seem to be affected at all.

Hunting also causes extinction


Kolbert also suggests that humans partly cause the sixth mass extinction by hunting. The argument is that humans hunted animals with long gestation periods and low birth rates, so by the time humans had killed enough of the animals, there were no new animals to repopulate the species. For example, elephants’ gestation period is almost two years long, and elephants typically only give birth to one elephant at a time. If humans hunt a herd of elephants, they would quickly deplete the whole population.


Kolbert's Pulitzer Prize-winning account of humans' catastrophic impact on several species is a must-read for anyone who needs a reminder that humans are the worst thing ever. Kolbert travels with various groups of scientists to different parts of the world to explore the causes and ramifications of various species' extinctions that are happening currently. The book is sad and maddening and largely hopeless because many of the species under threat today will assuredly disappear within the next 50 years.

The book is not too scientific for the average reader, but it might require close attention. We listened to the audio book and needed to supplement with a hard copy to get all the details. We like the mix of historical and contemporary, but we wish the book offered more solutions for ways to combat the sixth mass extinction. We expected a book like The World According to Monsanto, but we got one more like Salt, Sugar, Fat. Regardless, we love the book and want anyone who purports to care about the planet to read it.