Jonathan B. Mabry, Desert Archaeology, Inc.
After a relative lull, scientific interest in the peopling of the Americas is increasing again, and the southwestern U.S. has recently hosted some well-attended meetings at which this hot topic was debated. Following closely on the heels of the “Clovis and Beyond” conference in Santa Fe, New Mexico (see related article), anthropologists from all three of Arizona’s state universities met in Tempe, Arizona on December 4, 1999, at a conference entitled “Pioneers on the Land: How North America Got Its People.” During this intensive one-day colloquium, faculty from Arizona State University (ASU), University of Arizona (UA), and Northern Arizona University (NAU) gathered to present and discuss data from the fields of genetics, linguistics, archaeology, physical anthropology, and geoscience that bear on the initial human colonization of the New World.
Genetic data comprised a major topic. Mike Hammer and Tanya Karafet (UA) summarized studies of Y-chromosome variability among contemporary Native Americans and Asians. They identified two “paternal haplotypes” (male genetic lineages) among Native Americans that represent founder populations, and some possible source populations in the Lake Baikal region of northeast Asia.
Steve Zegura (UA) reviewed a variety of genetic evidence related to the timing, source populations, and number of migrations involved in the peopling of the Americas. He concluded that the two founding Y-chromosome haplotypes described by Hammer and Karafet originated in northeast Asia between 24,000 and 20,000 years ago. He argued that a patrilocal organization, in which women married into groups other than their parents’, thereby spreading their genes, would explain why only one maternal founding haplotype has been identified by some researchers studying variability in Native American mitochondrial DNA (mtDNA).
The two major linguistic models of the peopling of the Americas were summarized and assessed by Jane Hill (UA). Based on very different methods, the models also diverge in terms of the numbers, timings, and routes of early migrations they reconstruct. One model supports an inland migration from northern Eurasia about 12,000 years ago, whereas the other model reconstructs three pre-Clovis migrations, with the first originating in Australasia before 20,000 years ago, and the next two originating from the Pacific Rim of Asia (see related article).
Clues provided by flaked stone artifacts were also discussed. Jeff Brantingham (UA) summarized what is known about late Pleistocene flaked stone technology in northeast Asia, explaining that the Upper Paleolithic of Mongolia and southern Siberia was dominated by flat blade technology and generalized tool forms. During the waning of the last Ice Age, between about 17,000 and 11,000 years ago, microblade technology was ubiquitous throughout northeast Asia. In contrast, Clovis lithic technology in North America was dominated by prismatic blades and more formal tools (particularly the projectile points); microblades were rare. Brantingham concluded that, because of its generalized character, the lithic technology of northeast Asia could be the source for Clovis lithic technology. However, he pointed out that the presence of microblades at Paleoindian sites in northwestern North America—and their rarity to the south—are not explained by that scenario.
The first human uses of the southern Rocky Mountains were reconstructed from the distributions of Paleoindian projectile point types by Bonnie Pitblado (UA). She pointed out that fluted points are rare, and Angostura points are the most commonly found Paleoindian point type in that region. Based on the known time span of this type, the initial occupation of the higher elevations of western North America can be bracketed between 9,700 and 7,500 radiocarbon years b.p. (uncalibrated). Site locations and artifact characteristics indicate that this late Paleoindian population lived in the mountains year-round, was adapted to highland environments, and was distinct from its contemporaries in the West.
Because the most common type of early point in the Great Basin and on the Colorado Plateau is the Great Basin Stemmed, Pitblado suggested that the early Holocene populations of these regions were related. However, Angostura points are the second most common type of early point on the Colorado Plateau and in the mountains at the basin-plateau interface; its prominent presence may indicate a relationship with the late Paleoindian population of the southern Rockies, as well.
Todd Surovell (UA) considered a Paleoindian paradox: If the Monte Verde II site in Chile indeed predates the Clovis complex of North America by more than a millennium, and if humans entered the New World by the Bering land bridge, how could they travel more than 13,000 kilometers without leaving a trace along the way? A coastal migration route, with the earlier North American sites now submerged, giving the appearance that humans arrived first in South America, is one possible answer. To explore the necessary conditions for arrival at Monte Verde before migration into inland North America, Surovell simulated a coastal migration. He concluded that the population would have been spread too thin: “the coastal migration hypothesis is fundamentally flawed because it requires hunter-gatherers to exist under conditions in which they could not maintain viable populations.” He suggested three alternative possibilities, in order of plausibility: 1) Earlier sites exist in North America, but have not yet been discovered or accepted; 2) Monte Verde II is not as old as it is thought to be—either it is not a site, or the original stratigraphy is not intact; or 3) people came across the ocean directly to South America. None of these explanations are mutually exclusive, he added.
Continuing on the theme of colonization, Michael Barton, Steve Schmich, and Steve James (ASU) presented the results of simulations based on the ecological factors potentially involved in the initial colonization of empty landscapes. The simulations predict that first colonizers, because they don’t know details about resources on a landscape, tend to focus on low-cost/high-return resources initially. These types of resources are easily depleted locally, leaving only two options: move to another area or shift to higher-cost/lower-return resources. Before a landscape is fully populated, it is “cheaper” to move, but once a landscape is populated and high-return resources are depleted, people reduce their mobility and shift to lower-return resources. They also begin to exploit a higher diversity of resources as their knowledge of the local landscape increases. Barton and his colleagues concluded that the Clovis pattern matches the model for first colonizers. If there were groups before Clovis, they were ineffective competitors, because the Clovis people behaved as if they were colonizing an empty landscape. A second conclusion was that initial colonizers will move as soon as procurement costs rise, before resources are exhausted, because movement costs are low when they are not competing with anybody. The faunal record of Paleoindian times was also reviewed.
Jim Mead (NAU) focused on the timing of the extinctions of late Pleistocene megafauna in the dry cave record of the Southwest. He observed that the disappearance of mammoths, ground sloths, mountain goats, and other megafauna in this region is bracketed between 11,300 and 10,900 radiocarbon years b.p. (uncalibrated), about the same time span as the Clovis culture. With examples, he showed that much information about Paleoindian environments in the Southwest is represented in the pollen and plant parts preserved in the dried dung of these animals.
Larry Agenbroad (NAU) reported some new discoveries of terminal Pleistocene remains of mammoths in the Southwest and California, and noted that almost a third of the mammoth sites in North America younger than 15,000 years old also have cultural remains. He sees this as strong evidence of human predation playing a role in the extinction of New World elephants. He believes that the Clovis culture is the best candidate for this feat. In his opinion, the archaeological record of North America includes no substantial evidence for pre-Clovis peoples. “If there were pre-Clovis people, then they were impoverished, frugal, and remiss in terms of reproduction,” he remarked.
Geoff Clark (ASU) critiqued the recently revived model, based on similarities between tool technologies, of a connection between the Clovis and Solutrean cultures of North America and western Europe, respectively. He pointed out that similarities can develop between the tool technologies of unrelated peoples because of the inherent possibilities and limitations involved in making tools. He argued that neither Clovis nor Solutrean represent “cultures” like the identity-conscious social units known historically, and that they should be treated as different kinds of analytical units. He also suggested that “migration” is an inappropriate concept for Paleolithic archaeology; he believes that models of range extension by hunter-gatherers are more appropriate.
The “Pioneers on the Land” conference, like the larger “Clovis and Beyond” meeting that preceded it, included varied conclusions from different types of data. Perhaps the biggest challenge for scientists grappling anew with the origins of the first Americans and how the New World was initially colonized is to develop models that integrate the different lines of evidence. Some initial steps in that direction were taken that day in Tempe, and the planned publication will be eagerly read by scholars.