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By Root 1846 0

Haynes drew attention to the correlation between the birth of “an ice-free, trans-Canadian corridor” and the “abrupt appearance of Clovis artifacts some 700 years later.” Thirteen thousand to fourteen thousand years ago, he suggested, a window in time opened. During this interval—and, for all practical purposes, only during this interval—paleo-Indians could have crossed Beringia, slipped through the ice-free corridor, and descended into southern Alberta, from where they would have been able to spread throughout North America. The implication was that every Indian society in the hemisphere was descended from Clovis. The people at Blackwater Draw were the ancestral culture of the Americas.

Haynes was the first to put together this picture. The reaction, he told me, was “pretty gratifying.” The fractious archaeological community embraced his ideas with rare unanimity; they rapidly became the standard model for the peopling of the Americas. On the popular level, Haynes’s scenario made so much intuitive sense that it rapidly leapt from the pages of Science to high school history textbooks, mine among them. Three years later, in 1967, the picture was augmented with overkill.

If time travelers from today were to visit North America in the late Pleistocene, they would see in the forests and plains an impossible bestiary of lumbering mastodon, armored rhinos, great dire wolves, sabertooth cats, and ten-foot-long glyptodonts like enormous armadillos. Beavers the size of armchairs; turtles that weighed almost as much as cars; sloths able to reach tree branches twenty feet high; huge, flightless, predatory birds like rapacious ostriches—the tally of Pleistocene monsters is long and alluring.

At about the time of Clovis almost every one of these species vanished. So complete was the disaster that most of today’s big American mammals, such as caribou, moose, and brown bear, are immigrants from Asia. The die-off happened amazingly fast, much of it in the few centuries between 11,500 and 10,900 B.C. And when it was complete, naturalist Alfred Russell Wallace wrote, the Americas had become “a zoologically impoverished world, from which all of the hugest, and fiercest, and strangest forms [had] recently disappeared.”

The extinctions permanently changed American landscapes and American history. Before the Pleistocene, the Americas had three species of horse and at least two camels that might have been ridden; other mammals could have been domesticated for meat and milk. Had they survived, the consequences would have been huge. Not only would domesticated animals have changed Indian societies, they might have created new zoonotic diseases. Absent the extinctions, the encounter between Europe and the Americas might have been equally deadly for both sides—a world in which both hemispheres experienced catastrophic depopulation.

PALEO-INDIAN MIGRATION ROUTES

North America, 10,000 B.C.

Researchers had previously noted the temporal coincidence between the paleo-Indians’ arrival and the mass extinction, but they didn’t believe that small bands of hunters could wreak such ecological havoc. Paul Martin, a paleontologist who was one of Haynes’s Arizona colleagues, thought otherwise. Extinction, he claimed, was the nigh-inevitable outcome when beasts with no exposure to Homo sapiens suddenly encountered “a new and thoroughly superior predator, a hunter who preferred killing and persisted in killing animals as long as they were available.”

Imagine, Martin said, that an original group of a hundred hunters crossed over Beringia and down the ice-free corridor. Historical records show that frontier populations can increase at astonishing rates; in the early nineteenth century, the annual U.S. birthrate climbed as high as 5 percent. If the first paleo-Indians doubled in number every 20 years (a birthrate of 3.4 percent), the population would hit 10 million in only 340 years, a blink of an eye in geological terms. A million paleo-Indians, Martin argued, could easily form a wave of hunters that would radiate out from the southern end of the ice-free