Criticism — From the November 2015 issue

Rethinking Extinction

Toward a less gloomy environmentalism

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We now know that 99.9 percent of all species that ever existed are extinct. But until the end of the eighteenth century, the idea that any species had gone extinct was almost unknown. Nature was seen as a steady state, an unchanging tableau, not a process. Thomas Jefferson, whose passions included natural history, put it this way:

Such is the economy of nature that no instance can be produced of her having permitted any one race of her animals to become extinct; of her having formed any link in her great work so weak as to be broken.

The discovery of extinction is generally credited to Georges Cuvier, who taught at the Museum of Natural History in Paris and, in his spare time, studied the ancient bones in its collection. In 1796, Cuvier delivered a public lecture in which he announced that he had identified two lost species: the mastodon and the mammoth. By 1812, when he published a landmark four-volume treatise on fossil animals, he and others had identified forty-nine vanished species, including a cave bear, a pygmy hippopotamus, and a pterodactyl.

Cuvier’s discovery touched off a revolution in our understanding of nature that is still, in some ways, incomplete. In the years that followed his treatise, debate raged over the causes of extinction. Cuvier believed that extinctions were the result of planetary catastrophes, a view compatible with the Bible’s great deluge. Within a few decades, however, an alternative view propounded by the Scottish geologist Charles Lyell had won the day. Lyell argued that extinction happened gradually, over millennia, not in cataclysmic spasms. It would not be until 1980, when a study connected the extinction of the dinosaurs to the impact of an asteroid, that the possibility of abrupt mass extinction was again taken seriously.

Falling Bough, by Walton Ford. Courtesy the artist and Paul Kasmin Gallery, New York City

Falling Bough, by Walton Ford. Courtesy the artist and Paul Kasmin Gallery, New York City

Scientists now recognize that both mass and gradual extinctions have occurred. Mass extinctions get more press: five of them are known to have happened so far, and some say we are now embarking on a sixth, with humans playing the part of the asteroid. Yet scientists have calculated that the Big Five together account for only 4 percent of the extinctions that have taken place over the past 600 million years. The rest occurred in the absence of a global cataclysm.

As Elizabeth Kolbert recounts in The Sixth Extinction (2014), Cuvier’s discovery of extinction opened the door to Darwin’s discovery of evolution. If old species could disappear, maybe new species could emerge. Darwin’s theory of natural selection put the two processes together. In Kolbert’s words, “Extinction and evolution were to each other the warp and weft of life’s fabric.” But Darwin, like Lyell, believed that the process of extinction was so gradual as to be practically imperceptible. The idea that a mass extinction could happen in our own time, and that we could cause it, required a mental leap that even Darwin wouldn’t take.

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