The Sixth Extinction: An Unnatural History

The Sixth Extinction (book)
Author Elizabeth Kolbert
Country United States, United Kingdom
Language English
Subject Conservation science, Wildlife, Epochs, Holocene extinction, The Anthropocene, Geology, Archaeology, Biology, Zoology, History of mass extinctions
Genre Nonfiction popular science
Published 2014 (Henry Holt & Company)
Media type Print
Pages 319
OCLC 853618709
LC Class QE721.2.E97 K65 2014
Preceded by Field Notes from a Catastrophe
Text The Sixth Extinction (book) at the book publisher's website

The Sixth Extinction: An Unnatural History is a 2014 nonfiction book written by Elizabeth Kolbert and published by Henry Holt & Company. The book covers past mass extinctions and demonstrates that the earth and humans are in the midst of a "sixth" mass extinction. She chronicles previous mass species extinction events, as well as specific species extinguished by humans thousands of years ago, centuries ago, such as the great auk; and she includes the accelerated widespread extinction of many species during our present time. Kolbert also describes prehistoric and historic ecologies surrounding prior and near-present species extinguishing events.

The target audience is the general reader, and scientific descriptions are rendered in understandable prose for the lay reader. The clear writing blends explanations of her treks to remote areas with interviews of scientists, researchers, and guides; without advocating a position, while maintaining objectivity. Hence, the sixth mass extinction theme is applied to flora and fauna existing in diverse habitats such as the Panamanian rainforest, the Great Barrier Reef, the Andes, Bikini Atoll, city zoos and the author's "own backyard". The book also applies this theme to a number of other habitats and organisms throughout the world and its oceans. When researching the current mainstream view of the relevant peer reviewed science, she estimates flora and fauna loss by the end of this century to be between 20% to 50% "of all living species on earth".[1][2][3][4][5][6]


Kolbert also equates general current unawareness of this issue to the previous widespread disbelief during the centuries preceding the late 1700s; at that time it was believed that prehistoric mass extinctions had never occurred. It was also believed there were no natural forces powerful enough to extinguish species en masse. Likewise, in our own time, the possible finality presented by this issue results in denialism. Human behavior disrupts earth's balanced and interconnected systems "putting our own survival in danger." Consequently, the earth systems currently affected are: the global atmosphere, the water cycle, the ocean's thermal or heat absorption, ocean acidity and coral reefs, soil moisture and drought conditions, plant destruction by pests or non-indigenous fauna or heat stress, heat regulation by the earth's ice, and so on.

The human species contributes to this disruption - even without intending to - because of our innate capabilities to alter the planet at this stage of our cultural evolution; for instance, we now have the ability to harness energy from beneath the earth's surface. Homo sapiens also has the ability to adapt relatively quickly to almost any environment on this planet's surface. Other species, however, have a hard time relocating to new, suitable habitats. They are unable to migrate ahead of current rapid ecological changes, or are hampered by artificial barriers such as, for example, roadways, cityscapes, and suburban sprawl, which cause increased discontinuity between viable habitats throughout world.[1][2][3][4][5]

The author

Elizabeth Kolbert, a science writer, is a staff writer at The New Yorker magazine, and is the author of Field Notes from a Catastrophe and several other books. Her writing focuses on the effects of humans and civilization on our planet’s ecosystem. She writes her experiences of various locations, as noted above. Previously, she was a reporter for the New York Times.[1][3] Kolbert resides in Williamstown, Massachusetts with her husband and children, and she writes in her home office across from Mount Greylock in Massachusetts.[7] Pertaining to this book, Kolbert has been interviewed by national news and media organizations.[8][9][10][11][12]


Kolbert's decision to write this book followed first from a 2008 National Academy of Sciences paper that she fortuitously read. This paper is entitled "Are We In the Midst of The Sixth Extinction". The second step toward writing this book came out of an article she wrote for the New Yorker magazine. This involved becoming aware of the condition of amphibians in Panama. She realized that she "hadn't scratched the surface, that there was a book there." [6][13]

Summary of Chapters

Chapter 1: The Sixth Extinction

The ancestors of the frogs crawled out of the water around 400 million years ago. 250 million years ago, frogs were the earliest representation of what would become the modern amphibian orders. Amphibians have been on Earth for longer than mammals or birds; they were even here before dinosaurs. Recently, it has been reported that the extinction rate of frogs is increasing. Based on these alarming rates, we can predict an event of similarly catastrophic nature was headed our way. [14] A decade ago, Panamanian golden frogs were plentiful in numbers and easy to find around Panama. However, within the past couple of years, the frogs started to disappear. Kolbert states that studies by the National Zoological Park in Washington D.C and a mycologist at the University of Maine prove the reason for the increased mortality of Panamanian frogs is due to a type of Chytrid fungi.[15] However, Chytrid fungi are not naturally found in Panama. This left a puzzling question: how did the fungi get to Panama if it doesn’t naturally live there? Evidence indicates that humans are actually how the fungi traveled. Kolbert uses the frog-fungi relationship as a symbol of how humans are introducing invasive species to species who would normally have the proper distribution of alleles for their environment.

Chapter 2: The Mastodon’s Molars

Kolbert explains how fossils of the American mastodon (Mammut americanum) shaped Georges Cuvier’s views on catastrophism. According to Cuvier, there was no reason the mastodon should have died out. The mastodon was large enough to avoid predation, had large enough teeth to consume an abrasive diet, and other phenotypes that would increase their survival. Cuvier concluded there must be sudden and violent natural catastrophes that would be causing such mass extinction of viable species. [16] Kolbert uses the mastodon as a symbol for the idea that catastrophe is an important mechanism of extinction.

Chapter 3: The Original Penguin

The great auk was a large flightless bird that lived in the Northern Hemisphere. It has a large, intricately grooved beak. When the first settlers arrived in Iceland, the auk’s population was probably in the millions. However, the settlers found the auk’s to be “very good and nourishing meat.” They also used them for fuel, fish bait, and for stuffing mattresses.[17] Kolbert uses the great auk as a symbol of how human overexploitation resources is an important mechanism of extinction.

Chapter 4: The Luck of the Ammonites

Kolbert explains that the main cause of the Cretaceous-Paleogene extinction event was not the impact of the asteroid itself. It was the dust created by the impact. The debris from the impact incinerated anything in its path.[18] She states that it is impossible to give anything near a full account of the various species that died out due to this catastrophe. Kolbert explains that even though amniotes were ‘fit’ for their current environment, a single moment can completely change which traits are advantageous and which are lethal. [19]

Chapter 5: Welcome to the Anthropocene

Kolbert uses the extinction of graptolites and other clades to explain glaciation as a mechanism for extinction. When carbon dioxide levels in the air are high, there typically is an increased level in temperatures and in sea level. Right around the time graptolites went extinct, carbon dioxide levels dropped. Temperatures fell and sea levels plummeted. This caused a change in the chemistry of the ocean. This can cause a devastating impact on life forms.[20] Kolbert states that human activity has transformed between a third and a half of land surface on the planet. We have dammed most of the major rivers of world, increased levels of nitrogen than can be fixed naturally by terrestrial ecosystem, used more than half of the world’s readily accessible freshwater run-off, removed more than one third of the primary producers of the oceans’ coastal waters, and changed the composition of the atmosphere by deforestation and fossil fuel combustion. [21]

Chapter 6: The Sea Around Us

Since the beginning of the industrial revolution we have seen increasing levels of carbon dioxide in the atmosphere at an alarming rate. Studies show we have added approximately 365 billion tons by burning of the fossils fuels and an additional 180 billion tons by deforestation. We add another 9 billion tons or so a year, an amount that has been increasing 6% annually. Essentially, we have increased the concentration of carbon dioxide in the air to higher than it has been in the last several million years. [22] Some of this carbon dioxide is being absorbed by our oceans to create carbonic acid. This is lowering the pH of our ocean and killing many of our marine life. Kolbert uses the drastic decline in life forms around the Castello Aragonese as a warning sign of what is to come if we continue to increase carbon dioxide levels in the atmosphere. [23]

Chapter 7: Dropping Acid

Coral reefs support thousands of species by providing food and protection. Subsequently, many species have co-evolved with corals. Due to ocean acidification, it is very possible that corals will become extinct by the end of the century. Prior to the Industrial Revolution, under water reefs had an aragonite saturation state between 4 and 5. However, if current emission intensity remain as they are today, by 2060, there will no longer be a region above 3.5. This will lead to an increase in energy needed for calcification.[24] The same energy that will be expended on calcification is vital to recover from being eaten away by marine species and being battered by waves. Corals prove to be a symbol of ocean acidification as mechanism of extinction.

Chapter 8: The Forest and the Trees

Global warming is most commonly seen as a threat to cold-loving species. As temperatures rise, the ice at the North Pole and South Pole will melt. Any animal that depends on the ice will be faced with extreme challenges that could ultimately drive them to extinction. [25] Kolbert surfaces attention to the fact that the poles are not the only place affected by global warming. She explains that climate change is a major force in mass extinction.[26]

Chapter 9: Islands on Dry Land

Kolbert points out how everything in life is interconnected. She traces how there is circus-like complexity in the life-forms of many species. She explains that one minor change causes a domino effect in various ecological systems. [27] [28] [29]

Chapter 10: The New Pangaea

Kolbert points out there is an evolutionary arms race in which each species must be equipped to defend against than any of their potential predators and to be more fit than their competition. For example, the new host has no defense if encountered by a new fungus, virus, or bacteria. This can be extremely deadly.[30] There was an example of this in the eighteen hundreds. The American chestnut was the dominant deciduous tree in the eastern forests. Then, a fungus (Cryphonectria parasitica) started to cause chestnut blight. It was nearly 100% lethal. The fungus was unintentionally imported to the U.S.[31] This furthers the idea of the first chapter that invasive species are a mechanism of extinction.

Chapter 11: The Rhino Gets an Ultrasound

The Sumatran Rhino was once so abundant in numbers it was considered an agricultural pest. However, as Southeast Asia’s forests were cut down, the rhino’s habitat became fragmented. In the 1900s, the rhino population has been shrunk to just a few hundred. Today, there are only four living rhinos. [32] Kolbert uses the rhino to show habitat fragmentation as a mechanism of extinction.

Chapter 12: The Madness Gene

Europe was the home to Neanderthals for at least a hundred thousand years. Then, about 30,000 years ago, the Neanderthals vanished. Fossil records show that modern humans arrived to Europe 40,000 years ago. Within 10,000 years, Neanderthals were bred out.[33] Through molecular sequencing, we have found that there is 1-4 percent Neanderthal DNA in all non-African humans. This would mean humans and Neanderthals reproduced. Then those hybrids reproduced. The pattern continued until Neanderthals were literally bred out.[34] Kolbert states there is every reason to believe that Neanderthals would still exist if it weren’t for humans.

Chapter 13: The Things with Feathers

Kolbert concludes with the hope in humanity. Whether meaning to or not, we are deciding which evolutionary pathways will be shut off forever and which can be left open to flourish.


Some sources for the book are: The Song of the Dodo by David Quammen, The Ghost With Trembling Wings by Scott Weidensaul, as well as reports from Edward O. Wilson, a biologist. The pioneering studies of naturalist Georges Cuvier and geologist Charles Lyell are also referenced . The book's title is similar to a 1995 book titie, The Sixth Extinction: Patterns of Life and the Future of Humankind by Richard Leakey and Roger Lewin. Also included are interview results from a forest ecologist, atmospheric scientist Ken Caldeira, wildlife and conservation experts, a modern day geologist, and fungus research in New England and New York state.[3][5]

See also


  1. ^ a b c Gore, Al (vice president of the United States from 1993 to 2001) (2014-02-10). "Without a Trace. ‘The Sixth Extinction,’ by Elizabeth Kolbert". New York Times Sunday Book Review (New York). Retrieved 2014-07-10. 
  2. ^ a b Schulz, Kathryn (2014-02-09). "The Sixth Extinction Examines Human Overkillers and the Next Great Die-Off". New York Magazine (New York: New York Media LLC). Retrieved 2014-02-13. 
  3. ^ a b c d Kakutani, Michiko (2014-02-02). "Cataclysm Has Arrived: Man’s Inhumanity to Nature". New York Times (New York). Retrieved 2014-02-13. 
  4. ^ a b Hannibal, Mary Ellen (2014-02-09). "Sixth Extinction". The Huffington Post – Green (New York:, Inc). Retrieved 2014-02-13. 
  5. ^ a b c Darwall, Rupert (2014-02-14). "Book Review: 'The Sixth Extinction' by Elizabeth Kolbert". The Wall Street Journal (New York: Dow Jones & Company). Retrieved 2014-02-14. 
  6. ^ a b Anthony, Andrew (2014-03-16). "'"Elizabeth Kolbert: 'The whole world is becoming a kind of zoo. The Guardian – Green (London: Guardian News and Media Limited). Retrieved 2014-02-13. 
  7. ^ "Elizabeth Kolbert". Henry Holt & Co. Retrieved 2014-02-13. 
  8. ^ The New York Times. "A Conversation With". Science (section). 2014-02-10
  9. ^ NPR's Fresh Air. National Public Radio. February 12, 2014
  10. ^ The Daily Show February 11, 2014.
  11. ^ CBS This Morning. CBS News. February 9, 2014.
  12. ^ All Things Considered. National Public Radio. February 12, 2014.
  13. ^ Wake, D. B.; Vredenburg, V. T. (2008). "Are we in the midst of the sixth mass extinction? A view from the world of amphibians" (Free PDF download). Proceedings of the National Academy of Sciences 105: 11466 . Bibcode:2008PNAS..10511466W. PMC 2556420. PMID 18695221. doi:10.1073/pnas.0801921105. Retrieved 2014-03-16.  PNAS
  14. ^ Alroy, John (2009). "Speciation and Extinction in the Fossil Record or North American Mammals". Cambridge University Press. Speciation and Patterns of Diversity: 310–23. Retrieved 29 April 2014. 
  15. ^ Johnson, Paul. "Amphibian Chytrid Fungus". U.S Department of the Interior. National Park Service. Retrieved 27 April 2014. 
  16. ^ Cuvier, Georges. "Elegy of Lamarck". Edinburgh New Philsophical Journal. Journal 20: 1–22. Retrieved 27 April 2014. 
  17. ^ Gaskell, Jeeremy (March 15, 2001). Who Killed the Greak Auk?. New York: Oxford University Press. p. 87. ISBN . 
  18. ^ Officer, Charles; Page, Jake (May 2008). Rhodes, Stone, Mailamud, ed. Language of the Earth: A Literary Anthology (2nd ed.). Chichester, England: Wiley: John Wiley & Sons Inc. p. 183. ISBN . 
  19. ^ Zalasiewics, Jan (November 2, 2009). The Earth After Us: What Legacy Will Humans Leave in the Rocks?. New York: Oxford University Press. p. 2008. ISBN . 
  20. ^ Kiessling, Wolfgang (2011). Global Change Biology (First Paperback author2=Simpson, Carl ed.). New York: Oxford Printing Press. p. 56–67. ISBN . 
  21. ^ Zalewicz, Jan (2008). "Are We Now Living in the Anthropocene?". Geological Society of America Today (18): 6. 
  22. ^ Sabine, Chris. "PMEL CO2". National Oceanic and Atmospheric Administration-Pacific Marine Environmental Laboratory. Retrieved April 28, 2014. 
  23. ^ Kolbert, Elizabeth. "The Acid Sea". National Geographic Magazine. National Geographic Society. Retrieved 26 April 2014. 
  24. ^ Fabricus, Katherina; Chris Langdon; Sven Uthicke; Craig Humphrey; Sam Noonan; Glenn De'ath; Remy Okazaki; Nancy Muehllehner; Martin S. Glass; Janice M. Lough (29 May 2011). "Losers and Winners in Coral Reefs Acclimatized to Elevated Carbon Dioxide Concentrations". Nature Climate Change 1 (3). doi:10.1038/nclimate1122. Retrieved 28 April 2014. 
  25. ^ Barnosky, Anthony (2009). Heatstroke: Nature in an Age of Global Warming. Washington, D.C: Island Press/ShearwaterBooks. pp. 55–56. ISBN . 
  26. ^ Tripati, Arahdna; =Eagle, Robert; Roberts, Christopher. (28 June 2009). "Coupling of CO2 and Ice Sheet Stability Over Major Climate Transitions of the Last 20 Million Years". Science 326 (5958): 1394-1397. doi:10.1126/science.1178296. Retrieved 28 April 2014. 
  27. ^ Bierregaard, Richard; Gascon, Claude; Mesquita, Rita; Lovejoy, Tomas. (September 2001). Lessons from Amazonia The Ecology and Conservation of a Fragmented. New Haven, Conn.: Yale University Press. p. 41. ISBN . 
  28. ^ Wright, Emma. "Army Ant Camp Followers". Conservation: The Environment and Food Security. Retrieved 29 April 2014. 
  29. ^ Ellis, Erla; Ramankutty, Navin (2008). "Putting People in the Map: Anthropogenic Biomes of the World". Frontiers in Ecology and the Environment 6 (8): 439-447. doi:10.1890/070062. Retrieved 28 April 2014. 
  30. ^ Ricciardi, Anthony (21 Jan 2007). "Are Modern Biological Invasions an Unprecedented Form of Global Change?". Conservation Biology 21 (2): 329–336. doi:10.1111/j.1523-1739.2006.00615.x. Retrieved 29 April 2014. 
  31. ^ Rellou, Julia. "Chestnut Blight Fungus (Cryphonectria parasitica)". Introduces Species Project. Retrieved 28 April 2014. 
  32. ^ Welz, Adam (27 Nov 2012). "The Dirty War Against Africa's Remaining Rhinos". Yale University Press. 
  33. ^ Callaway, Ewen. "Modern human genomes reveal our inner Neanderthal". Nature: International Weekly Journal Of Science. doi:10.1038/nature.2014.14615. Retrieved 27 April 2014. 
  34. ^ Alroy, John (1999). Putting North America's End Pleistocene Megafaunal Extinction in Context. New York: Kluwer Acdamix/Plenum. p. 138. 

External links

  • Official website
  • Elizabeth Kolbert Reports On The Dire Consequences Of Climate Change. Dec 10, 2007.
  • Will We Be the Next Extinction?. Geri Spieler. Huffington Post – Books. Feb 11, 2014.
  • Enter the Anthropocene – Age of Man. Elizabeth Kolbert. National Geographic. March 2011.
  • Why is biodiversity in crisis?. "pressure that humanity is placing on the planet". International Union for Conservation of Nature. 2014.
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