In the early 1780s Thomas Jefferson, having just witnessed the birth of a nation, struggled to comprehend the death of an entire species. Jefferson wondered if it could be possible that the animal we know today as the mammoth had entirely ceased to exist. Gathering observations for one of this country’s first great scientific and literary masterpieces, Notes on the State of Virginia, Jefferson decided that the answer had to be no. His mind shackled by a venerable scientific theory known as the great chain of being–the notion that all life in God’s creation took the form of hierarchical links that could never be sundered–he refused to accept the reality of extinction. "Such is the economy of nature," 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." Waving away the absence of mammoths in the settled portion of the continent, Jefferson speculated that perhaps the elusive giant ranged outside the gaze of contemporary observers, lumbering throughout the landscape onto which he routinely projected his dreams for the young United States: the West.
Beyond bowing to the scientific state of the art, Jefferson the naturalist remained answerable to Jefferson the nationalist. Europe’s great cities might feature sumptuous palaces and vast cathedrals, he allowed, as well as libraries groaning beneath the weight of humankind’s accumulated knowledge and museums stocked with centuries’ worth of masterpieces. But the United States boasted natural wonders that beggared description. Abundance in the New World seemingly overflowed into limitlessness: forests stretching to the horizon, mountain ranges of surpassing majesty and curiosities like Virginia’s Natural Bridge, which Jefferson owned and labeled "the most sublime of Nature’s works." For Jefferson the patriot, America’s natural advantages counterbalanced Europe’s prodigious cultural patrimony. So in picking a fight with the Old World, he no doubt found it prudent to recruit a massive beast like the mammoth to his side.
A worldview in which extinction appeared beyond the pale of the natural order and an affront to national destiny now sounds at once anachronistic and alluring. Today we find ourselves in the midst of what scientists believe is the sixth great era of extinction. Five times previously, between 450 million and 65 million years ago, huge numbers of species died off, including during the Cretaceous period, when, after a gigantic asteroid or volcanic eruptions abruptly altered the earth’s environment, most of the dinosaurs shuffled off this mortal coil. The current wave of extinctions, which began within the past 100,000 years, is different; people are the cause of the disruption this time. As modern humans scattered across the globe, wherever they went they brought with them exotic diseases and seeds of invasive species. They exploited the resources they found: depleting fisheries, felling vast stands of timber and overhunting game. And as their numbers grew–from roughly 5 million 10,000 years ago to nearly 7 billion today–the habitats they despoiled precipitated the current crisis. By the century’s end, perhaps 50 percent of the now extant species will have died off. An alphabet soup of animals has already disappeared: the Arabian gazelle, the bulldog rat, the Caribbean monk seal. Hundreds of others are gone, and an unknown number will likely soon join them.
Mark Barrow is less concerned with gazing into the hazy future than clarifying the growing awareness of humankind’s role in extinction. In Nature’s Ghosts, he explains how naturalists, driven by affection for the nonhuman world, gradually became worried about the "specter of extinction" and eventually "mobilized to act." By following their example, Barrow suggests, we might still chart a course from this precarious moment to a future of biodiversity.