The Sixth Extinction: An Unnatural History.
Bloomsbury. 2014. 319 pp.
ISBN 978 1 4088 5121 0.
As Elizabeth Kolbert begins her book, she is in a market in the town of El Valle de Anton in Panama. It has, she says, "what must be the largest selection of golden frog figurines in the world," because, here, the golden frog is a lucky symbol. Once, there were thousands and thousands of golden frogs in the El Valle area, but by 2002 they had all disappeared. Scientists who decided to capture and breed a few in captivity were too late. It quickly became apparent that the golden frog and amphibians of all kinds were disappearing rapidly, not just in South America but also in Central America, Costa Rica, Australia, and many other places, too. The culprit was found to be a chytrid fungus that lives on the animal's skin and interferes with its metabolism.
The golden frog and many other amphibian species are now extinct in the wild, and amphibians are currently the world's most endangered species. Should that worry us? Yes, says Kolbert. Extinction takes place very rarely in geological time and usually very slowly. Sudden mass extinction, such as that which is currently happening to amphibians, and, worryingly, to other species such as reef-building corals, fresh-water molluscs, rays and sharks, and some species of mammal, is usually associated with a sudden change in the environment caused by a catastrophe of some kind. So, what is happening?
One major factor cited by Kolbert is "intercontinental reshuffling"—the ease with which animals and organisms are transported around the world. Recent concern about the spread of the SARS virus is one example of the danger this poses. But there are other things which are changing the environment. And who is responsible for this? "One weedy species." Us.
Having pointed the finger, Kolbert digresses into an interesting history of the way in which the concept of extinction came about. Not until the 18th century was there any idea that a species might die out. Huge fossilized bones were found and studied in America in 1739, and they were argued over for years, but it was assumed that the animal from which they came was "still out there somewhere." Not until Frenchman George Cuvier made a close study of as many of these huge bones as he could collect, did the idea of a vanished species arise. In 1800, Cuvier determined that there were at least four species of animal that no longer existed, but he argued with Jean Baptiste Lamarck as to whether these animals were a separate species or were creatures that had "transformed" (evolved) into animals that currently existed.
Kolbert follows this argument through, introducing seminal figures in the debate, such as Charles Lyell, whose Principles of Geology strongly influenced Charles Darwin. She also discusses those who proposed and argued over various theories about the cause of mass extinctions. And she brings the arguments up-to-date by visiting places where important discoveries have been made and talking to scientists, ecologists, geologists, conservationists, and others whose current work adds to the debate. Her style is journalistic, which makes for easy reading. But her habit of introducing each person by their physical attributes gets rather wearing: x is lanky, long faced, with bushy eyebrows; y wears a silver ear-ring in each ear and has a large tattoo; z has curly brown hair and a boyish smile; and so on.
Five mass extinctions are known, and Kolbert discusses each of them. This current "Sixth Extinction" as she has called it is, like the others, put down to sudden change—caused, not as earlier mass extinctions apparently were by an asteroid strike or a massive volcanic eruption, but by our disruption of the Earth's biological and geochemical systems.
Can we stop it? Halfway through this book, reading of the first appearance of homo sapiens and our supposed culpability in the extinction of the Megafauna and also of our close relatives, the Neanderthals, ten thousand years ago, and reading of our continuing responsibility for the loss of various species of birds, bats, trees etc., I began to find the book depressing. Kolbert, however, is not a doom-monger. She pins her hope on "our restlessness, our creativity, our ability to cooperate to solve problems and complete complicated tasks." But at the same time, she believes that we are now at the point of "deciding, without quite meaning to, which evolutionary pathways will remain open and which will forever be closed."
Kolbert's accounts of her travels, her descriptions of specific events and of particular animals and historical developments, are all good reading. The overall message, however, is clear: the Sixth Extinction is ongoing, and it will change our world. Whether we will survive or not, we don't know, but we should heed the warning of ecologist Paul Ehrlich, who wrote that "in pushing other species to extinction, humanity is busy sawing off the limb on which it perches."
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