IV.

Clovis-First Theory

The age of the earliest Clovis sites coincided neatly with geological evidence that by 11,500 years ago the Laurentide and Cordilleran ice sheets had retreated far enough to open a habitable ice-free corridor—a fact first recognized by University of Arizona archaeologist C. Vance Haynes. It appeared that Clovis groups had moved south from Alaska through the continental interior right after it became possible to do so. That no sites older than Clovis were found, at least initially, seemed to confirm that Clovis people were the first colonizers of the Americas.

A.

Rapid Migration

Once they had traveled south of the ice sheets, Clovis groups spread rapidly. Soon after 11,500 years ago, Clovis and Clovis-like materials appear throughout North America. The oldest sites are in the Great Plains and the southwestern United States; younger sites are found in eastern North America. No subsequent group would achieve such a wide distribution in North America. But Clovis groups did not stop in North America. According to the Clovis-first theory, they must have continued on to South America. As these groups pushed south, the traditional thinking went, they developed different tools and other artifacts that were no longer readily recognizable as Clovis. They arrived at Tierra del Fuego on the southern tip of South America within 1,000 years of leaving Alaska.

The rapid dispersal of Clovis peoples throughout the hemisphere was remarkable given the landscape they traversed. Not only did they travel through desert, plains, and forest, they did so during the environmental upheaval that marked the end of the last Ice Age. Climates were growing warmer—drier in some areas and wetter in others—and the distributions of plants and animals were shifting in complex ways in response to the changing climates. As they entered each new habitat they must have quickly learned to find suitable plant and animal foods. They would need stone to repair their toolkits, freshwater to drink, and the ability to overcome environmental challenges encountered along the way.

B.

Big-Game Hunters

A long-favored explanation for the rapid spread of Clovis people was that they preyed on large animals, such as mammoth and mastodon. These animals were themselves wide-ranging in their distribution. Archaeologists believed a reliance on big-game hunting meant that Clovis groups would have less need to learn about available local resources.

Archaeologists initially found some support for the big-game hunting hypothesis in archaeological excavations, as well as in the Clovis toolkit itself. Along the San Pedro River in Arizona, for example, are four Clovis sites separated by less than 20 km (12 mi). Each site yielded Clovis points embedded in the skeletons of mammoths. So similar are the points at these sites that they may be the handiwork of a single group, which obviously found good hunting in the area. The artifacts at San Pedro and other Clovis sites include a variety of tools handy for hunting, killing, and butchering game animals. There are the distinctive fluted spearpoints, shown experimentally by University of Wyoming archaeologist George Frison to be capable of bringing down elephant-sized animals. In addition, there are stone knives, scrapers, gravers (tools for scoring bone), drills, and a few preserved artifacts of ivory and bone. These tools, which occur in Clovis sites across North America, support the view that Clovis peoples were practicing the same way of life.

Clovis tools were typically made of superior quality fine-grained stone, including chert, jasper, and chalcedony. Such stone is durable and readily flaked by skilled toolmakers into a desired, sharp-edged form. More important, it is easily resharpened and reused. That would be important to hunters pursuing wide-ranging big game. They could continue to use their stone tools as they tracked game far from the quarries where they acquired their stone. Analysis of these tools suggests that Clovis groups commonly traveled distances of 300 km (185 mi). In one instance, a dozen Clovis points quarried from the Texas Panhandle were left as a cache in northeastern Colorado, 485 km (300 mi) away. These distances indicate a range of movement across the landscape far greater than is observed in later periods of American prehistory.

C.

Big-Game Extinctions

The idea that Clovis people were big-game hunters could help explain an unsolved puzzle of the Americas in the late Pleistocene: the catastrophic extinction of dozens of species of large animals. Across the Americas millions of large animals—known as megafauna—disappeared. These animals included the mammoth, mastodon, and the giant ground sloth, as well as the horse, the camel, and many other herbivores. Some very large and formidable carnivores also died out, including the American lion, the saber-toothed tiger, and the giant short-faced bear. These extinctions were thought to coincide with the arrival of Clovis groups, a chronological coincidence that led University of Arizona ecologist Paul Martin to propose the hypothesis of Pleistocene overkill. This hypothesis, first put forward in 1967, contends that Clovis big-game hunters caused the extinctions. Martin suggested that overkill was especially likely—even inevitable—if Clovis groups were the first Americans. For if the megafauna had never before faced human hunters, they would have been especially vulnerable prey to this new, dangerous, two-legged predator.