on 13 February 2014
As a former invertebrate paleobiologist, "The Sixth Extinction: An Unnatural History" is the book I have been waiting for years to be written. It is a clarion call for ending the current mass extinction that we humans are causing, and a book that should be, according to Scientific American, "this era's galvanizing text", worthy of comparison with Rachel Carson's "Silent Spring". It is also a vastly superior popular science book than last year's "Scatter, Adapt, and Remember: How Humans Will Survive a Mass Extinction" written by IO9 science editor Annalee Newitz, simply because Elizabeth Kolbert, a staff writer at The New Yorker, has done a superlative job in science reporting, accurately reporting and interpreting work done by some of the most notable researchers of our time studying mass extinctions, whether it is research from Berkeley vertebrate paleobiologist Anthony Barnosky (The lead author of a 2011 Nature paper estimating that current extinction rates are equivalent to those of the five great mass extinctions recognized from the fossil record; the terminal Ordovician, terminal Permian, terminal Triassic and the terminal Cretaceous; the latter in which non-avian dinosaurs became extinct.) or American Museum of Natural History curator of invertebrate paleontology Neil Landman, a noted researcher of Cretaceous ammonites, or evolutionary geneticist and anthropologist Svante Paabo, whose team is sequencing the entire Neanderthal genome and recognized the existence of another late Pleistocene hominid species, the Denisovans, from genomic material in a fragment of a finger bone found in a Siberian cave. What Kolbert has written is a spellbinding work of science journalism worthy of comparison with David Quammen's "The Song of the Dodo: Island Biogeography in an Age of Extinctions", and one that belongs on the bookshelves of anyone interested in science, and especially those who may not grasp the full extent of the ongoing mass extinction being caused by us, humanity. Moreover, at the end of her book, she provides an extensive bibliography which notes many of the most important relevant scientific papers as well as important texts written by the likes of notable ecologists James H. Brown and Michael Rosenzweig, and paleobiologists Michael Benton, Douglas Erwin and Richard Fortey. Without question, "The Sixth Extinction: An Unnatural History", may be one of the most discussed, most important, books of popular science published this year.
In her opening chapter, "The Sixth Extinction", in prose that is hauntingly beautiful and poignant, Kolbert cites the disappearance of Panamanian frogs and toads as one emblematic of the ongoing crisis in biodiversity, noting that of all the major groups of terrestrial vertebrates, amphibians are the ones which are most rapidly going extinct before our very eyes. She uses the discoveries of fossil mastodons and mammoths in North America and Europe in the 18th and early 19th Centuries in the second chapter ("The Mastodon's Molars") to introduce readers to the great French naturalist Georges Cuvier who was the first to recognize the existence of extinct species and the likelihood that they died during great cataclysms in Earth's history. Her third chapter, "The Original Penguin", is an especially lucid account of British geologist Charles Lyell's uniformitarian view of Earth's history, and how that inspired Charles Darwin's thinking, not only in geology, but especially, in his conception of the Theory of Evolution via Natural Selection, while describing the rapid extinction of the Great Auk - which was the first bird to be dubbed a "penguin" - in the North Atlantic Ocean along the northernmost coast of North America and Iceland. In the fourth chapter, "The Luck of the Ammonites", she offers an especially lucid account of geologist Walter Alvarez's discovery of the iridium-rich clay at the end of the Cretaceous, leading to the development of the asteroid impact theory for the Cretaceous mass extinction, while also discussing work by such notable invertebrate paleontologists as David Jablonski, David Raup, Jack Sepkoski, and Neil Landman, in noting how the Cretaceous mass extinction that wiped out the non-avian dinosaurs, ammonites and other notable terrestrial and marine organisms, was simply a case of bad luck, which she emphasizes further in describing the probable causes for the terminal Ordovician and terminal Permian mass extinctions (Chapter V).
Kolbert devotes two chapters (Chapters VI and VII) to the ongoing "experiment" humanity is performing on the world's oceans, ocean acidification, caused by an excessive increase in carbon dioxide being dumped into them, and noting that it was a likely cause for several of the mass extinctions known from the fossil record. I must commend her for an excellent discussion of the species-area curve known for decades by ecologists, especially through the important research by E. O. Wilson and his colleague Robert MacArthur in the early 1960s (Chapter VIII), as a means of understanding habitat fragmentation (Chapter IX) as a major contributing factor in determining a species' prospects for survival. There are also excellent discussions on how human activity has fostered the unexpected dispersal of animals and plants, creating, in essence a "New Pangea" (Chapter X), that has only accelerated the tempo of the ongoing mass extinction, and the "Pleistocene Overkill" hypothesis (Chapter XI) proposed by geologist Paul S. Martin that has been confirmed, in spectacular fashion, by palynological (fossilized pollen and spores) data from Australia and North America. She describes the extinction of Neanderthals as another, much earlier, example of human-driven extinction (Chapter XII) relying on the notable research by Svante Paabo and his team, noting the importance of the "Out of Africa" theory in explaining Homo sapiens' global dispersal, while also discussing Paabo's "leaky-replacement" hypothesis that accounts for Neanderthals' eventual replacement by Homo sapiens through interbreeding, resulting in hybrids whose descendants include all non-African populations of humanity, contributing between 1 and 4 percent within the genomes of non-African populations, remnants of the Neanderthal genome. In the concluding chapter (Chapter XIII), Kolbert acknowledges she has been amassing evidence demonstrating why the current mass extinction exists, and warning us that "...we are deciding, without quite meaning to, which evolutionary pathways will remain open and which will forever be closed. No other creature has ever managed this, and it will, unfortunately, be our most enduring legacy."