There have been five great die-offs in history. This time, the cataclysm is us.
Of the many species that have existed on earth—estimates run as high as fifty billion—more than ninety-nine per cent have disappeared. In the light of this, it is sometimes joked that all of life today amounts to little more than a rounding error.
Records of the missing can be found everywhere in the world, often in forms that are difficult to overlook. And yet extinction has been a much contested concept. Throughout the eighteenth century, even as extraordinary fossils were being unearthed and put on exhibit, the prevailing view was that species were fixed, created by God for all eternity. If the bones of a strange creature were found, it must mean that that creature was out there somewhere.
“Such is the economy of nature,” Thomas Jefferson wrote, “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.” When, as President, he dispatched Meriwether Lewis and William Clark to the Northwest, Jefferson hoped that they would come upon live mastodons roaming the region.
The French naturalist Georges Cuvier was more skeptical. In 1812, he published an essay on the “Revolutions on the Surface of the Globe,” in which he asked, “How can we believe that the immense mastodons, the gigantic megatheriums, whose bones have been found in the earth in the two Americas, still live on this continent?” Cuvier had conducted studies of the fossils found in gypsum mines in Paris, and was convinced that many organisms once common to the area no longer existed. These he referred to as espèces perdues, or lost species. Cuvier had no way of knowing how much time had elapsed in forming the fossil record. But, as the record indicated that Paris had, at various points, been under water, he concluded that the espèces perdues had been swept away by sudden cataclysms.
In his theory of natural selection, Darwin embraced extinction; it was, he realized, essential that some species should die out as new ones were created. But he believed that this happened only slowly. Indeed, he claimed that it took place more gradually even than speciation: “The complete extinction of the species of a group is generally a slower process than their production.” In “On the Origin of Species,” published in the fall of 1859, Darwin heaped scorn on the catastrophist approach:
So profound is our ignorance, and so high our presumption, that we marvel when we
hear of the extinction of an organic being; and as we do not see the cause,
we invoke cataclysms to desolate the world.
By the start of the twentieth century, this view had become dominant, and to be a scientist meant to see extinction as Darwin did. But Darwin, it turns out, was wrong.