Loosed upon herds of unwary animals, Paleo-Indians (hereafter, simply Indians) slaughtered them or stampeded them over cliffs. They chiseled long stone blades especially designed to penetrate thick hides. Archaeologists have named these hunters after their ingenious blades, first found at Clovis, New Mexico. Clovis blades have been found in nearly every state of the United States and even at the southern tip of South America.
Around 12,000 years ago, however, the big mammals were disappearing from the Western Hemisphere. Thirty-three species became extinct, including mammoths, mastodons, saber-toothed cats, giant beavers, horses, and camels. Perhaps the hunters killed off the big mammals; or perhaps the heavily furred animals were ill-suited to a warming trend.
The disappearance of these mammals nearly coincided with the closing of the route from Beringia to the Americas, as melting ice worldwide raised ocean levels hundreds of feet, flooding the low-lying land that had joined Asia and Alaska. No more big mammals could make their way into the Americas.
These two factors profoundly influenced the course of human development in the Americas: The absence of big mammals deprived Indian peoples of ready sources of food and draft animals, and the geographical isolation of the Americas meant that the Indians would not be exposed to the waves of biological diversity—plants, animals, bacteria, and viruses—that repeatedly washed over Europe, Asia, and Africa.
World History
