Standing more than twelve feet tall, this Columbian mammoth skeleton may be the largest in the world. Until it became extinct around 10,000 years ago, this species roamed the plains of North America—and was hunted by the early human inhabitants of the continent, who used spears to bring down mammoths and other big game.
THE UNITED STATES DEVOTES TWO NATIONAL holidays, Columbus Day and Thanksgiving, to celebrating the European “discovery” of America. No holidays celebrate the much earlier discovery of the Americas by the ancestors of the Indians. Yet archaeology suggests that, for sheer drama, the earlier discovery dwarfs the adventures of Christopher Columbus and the Pilgrims of Plymouth Rock. Within perhaps no more than a thousand years, Indians found a way through an Arctic ice sheet and swept all the way to Patagonia, at the southern tip of South America. At the end of that time they had populated two productive and unexplored continents.
The Indians’ march southward was the greatest expansion of our species’ range in the history of Homo sapiens. Nothing like it can ever happen again. It was marked by another drama: a mass extinction. When the first hunters arrived, they found the Americas teeming with big mammals that are now extinct: elephant-like mammoths and mastodons, three-ton ground sloths, beavers the size of bears, and sabertoothed cats, plus lions, cheetahs, camels, horses, and more.
What happened when humans met these beasts? Archaeologists and paleontologists disagree. The interpretation that makes the most sense to me is a “blitzkrieg”—a lightningfast assault in which the animals were quickly exterminated by humans, perhaps in just ten years at any given site. If that view is correct, it would have been the quickest and most severe extinction of big animals since the dinosaurs disappeared. It would also have been the first of many blitzkriegs that marred our mythical golden age of environmental innocence.
The Greatest Expansion in Human History
The confrontation between animals and the first people in the Americas was the last act in a long epic of human expansion. Spreading out of their center of origins in Africa, humans expanded into Asia and Europe, and then from Asia to Australia. This left North and South America as the last habitable continents without people. So how and when did people get to the Americas?
From Canada to the southern tip of South America, Indians look more like one another than the inhabitants of any other continent. They must have arrived here too recently to have evolved much genetic diversity. At the same time, American Indians resemble certain East Asian peoples. The evidence from both archaeology and genetics proves that Native Americans originated from Asia. The easiest route from Asia to America is across the Bering Strait, a narrow strip of water that separates Siberia and Alaska. Between twenty-five thousand and ten thousand years ago, during the Ice Age, sea levels were lower all over the world because so much water was locked up in ice. At that time, Siberia was linked to Alaska by a land bridge that is now under the Bering Strait.
Colonizing the Americas needed more than a land bridge. It also needed people to be living at the Asian end of the land bridge, in Siberia. Because of its harsh climate, the Siberian Arctic was not colonized until late in human history. But by twenty thousand years ago, mammoth hunters were living there, leaving stone tools and other traces of their presence. And stone tools similar to those of the Siberian hunters have been found in Alaska, dating from around twelve thousand years ago.
Once they had reached present-day Alaska, the Ice Age hunters found themselves separated from what is now the United States by another barrier. A broad ice cap stretched across Canada. Then, around twelve thousand years ago, a narrow, ice-free corridor opened up just east of the Rocky Mountains. We know that hunters soon moved south through that ice-free corridor, because their stone tools have turned up in archaeological sites south of the ice cap. At that point the hunters met America’s great beasts, and the drama began.
Archaeologists call these pioneering ancestral Indians the Clovis people because their stone tools were first recognized at a site near Clovis, New Mexico. Since then, Clovis tools or ones similar to them have been found throughout North America. These tools are much like the ones used by earlier eastern European and Siberian hunters, but with the addition of grooves on both sides of the stone spear points. These grooves made it easier to tie the stone points to sticks, but we don’t know whether the hunters threw their weapons or stabbed with them. Somehow, though, the hunters drove the points into big mammals hard enough to penetrate bone. Scientists have dug up mammoth and bison skeletons with Clovis points inside them.
The Clovis people spread quickly. The known sites in the United States were occupied for just a few centuries, just before eleven thousand years ago. Then Clovis points were replaced by smaller, more finely made tools called Folsom points. (These were discovered near Folsom, New Mexico.) These points are found with bison bones but never with mammoth bones.
Why did hunters switch from the Clovis spear points to the smaller Folsom points? Maybe they no longer needed the big points, because the biggest game animals were gone. There were no mammoths left. Camels, horses, giant ground sloths, and other big mammals had disappeared as well. Both North and South America lost large numbers of big mammal species at the same time.
As the human population has grown since 1800 (measured on the right), the number of species becoming extinct has steadily increased (shown on the left). The parallel lines raise the question: How many of these modern extinctions have humans caused?
Many paleontologists blame the extinctions on climate and habitat change at the end of the Ice Age. Yet the end of the Ice Age brought more habitat for animals, not less, as melting ice opened up areas of forest and grassland. Anyway, the big American mammals had already survived the ends of at least twenty-two earlier ice ages. In addition, both warmth-loving and cold-loving species went extinct, which should not have been the case if the cause was climate change.
Paul Martin of the University of Arizona described the outcome of hunter-meetsmammals as a blitzkrieg. In his view, the first hunters to emerge from the ice-free corridor thrived and multiplied because they found an abundance of big-game animals that had no fear of humans and were easy to hunt. When game was killed off in one area, the hunters and their offspring fanned out into new areas and killed the mammal populations there. By the time the hunters had reached southern South America, most big mammal species of the Americas had been exterminated.
Martin’s blitzkrieg theory has drawn vigorous criticism. Doubters ask: Could a small band of hunters passing through the ice-free corridor breed fast enough to populate two continents in a thousand years? Could they cover the eight thousand miles to southern South America in that time? Were Clovis hunters really the first people in the Americas? And could they have killed millions of big animals so efficiently that not a single individual of many species survived?
In modern times, when colonists have settled an uninhabited island, their population has grown as rapidly as 3.4 percent a year. This growth rate—four children per couple, and a new generation every twenty years—would multiply 100 hunters into 10 million in only 340 years. To reach the tip of South America in 1,000 years, humans would have had to expand southward an average distance of 8 miles a year, an easy task. Some migrations of Africa’s Zulu people in the nineteenth century are known to have covered 3,000 miles in 50 years.
As for whether the Clovis people were the first humans to spread south of the Canadian ice sheet, that’s a harder question. It’s also extremely controversial among archaeologists. Dozens of sites have been believed by a few researchers to contain evidence of human remains earlier than the Clovis people, but none of these supposed pre-Clovis sites is accepted without question by the whole scientific community.
In contrast, the evidence for the Clovis culture is undeniable, found in many places, and widely accepted. At site after site, archaeologists find a layer of Clovis tools with the bones of large extinct species. Above the Clovis layer is a younger layer of Folsom tools, but no bones of large mammals except bison. Below the Clovis layer lie thousands of years’ worth of fossils of large extinct mammals, but no human tools or remains. It makes good sense to me that the Clovis people were the first Americans.
MEADOWCROFT AND MONTEVERDE: UNANSWERED QUESTIONS
SOME ARCHAEOLOGISTS CLAIM TO HAVE FOUND evidence of human presence in the Americas before the time of the Clovis people. Almost all these claims raise questions about whether the material used for radiocarbon dating was mixed with older material, whether the dated material was actually found with human remains, or whether tools supposedly made by humans are really just naturally shaped rocks.
The two most nearly convincing of the claimed “pre-Clovis” sites are Meadowcroft Rockshelter in Pennsylvania, dated to about sixteen thousand years ago, and Monte Verde in Chile, South America, dated to at least thirteen thousand years ago. Monte Verde has many types of wellpreserved human artifacts, but the radiocarbon dating of these artifacts is open to question. At Meadowcroft there has been debate about whether the radiocarbon dates are accurate, especially because plant and animal species from the site are not thought to have lived there until much more recently than sixteen thousand years ago. Until questions about Monte Verde and Meadowcroft can be answered with more certainty, the Clovis people should be considered the oldest definitely known inhabitants of the Americas.
Another hotly debated argument about the blitzkrieg theory concerns the overhunting and extermination of big mammals. It seems hard to imagine Stone Age hunters killing mammoths at all, much less hunting them to extinction. Yet we know that Stone Age hunters who lived in what is now Ukraine, south of Russia, regularly killed mammoths—and built their houses out of neatly stacked mammoth bones. Picture a band of early American hunters spearing a terrified mammoth ambushed in a narrow streambed. Such hunts must have taken place many times.
Remember that the big mammals of the Americas had probably never seen humans before the Clovis hunters. Animals that evolved without humans around are surprisingly tame and unafraid. When I visited New Guinea’s isolated Foja Mountains, which have no human population, I found the large tree kangaroos so tame that I could approach within a few yards of them. Probably the big mammals of the Americas were killed off before they could evolve a fear of humans.
Could Clovis hunters have killed mammoths fast enough to exterminate them? Modern elephants are slow breeders that take about twenty years to reproduce their numbers. Prehistoric mammoths probably bred slowly, too. Few other large animal species breed fast enough to reproduce their numbers in less than three years. It could have taken Clovis hunters only a few years to kill off the large mammals in a given area and then move on to the next area.
The Clovis hunters probably killed often, too. A mammoth might have 2,500 pounds of meat, but to use all that meat would mean preserving it by drying it. Would you go to the work of drying a ton of mammoth meat when you could just go kill another mammoth? Hunters probably used only part of the meat from each kill, along with other desirable parts such as skins and tusks.
We are all too familiar with the blitzkriegs by which modern European and American hunters nearly wiped out bison, whales, seals, and many other large animals. We also know that similar blitzkriegs occurred on oceanic islands when earlier hunters reached unoccupied lands. How could it have been different when the Clovis hunters entered an unoccupied New World?
