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Emergence and Collapse of Early Villages
Models of Central Mesa Verde Archaeology
By Timothy A. Kohler, Mark D. Varien
UNIVERSITY OF CALIFORNIA PRESSCopyright © 2012 Regents of the University of California
All rights reserved.
Emergence and Collapse of Early Villages in the Central Mesa Verde
Timothy A. Kohler and Mark D. Varien
Two hundred and forty years after the last Pueblo people left Colorado, Hernán Cortés de Monroy y Pizarro—or maybe it was Quetzalcoatl—stepped onto the shores of Veracruz. Arriving at the Aztec capital of Tenochtitlan less than seven months later, the Spanish had no trouble recognizing kings and slaves, temples and markets, gods and warriors, and all manners of artifacts and other institutions, none of which had existed when the ancestors of these two societies last lived together in Eurasia. What accounts for the surprising mutual intelligibility of social forms between two societies that had shared their last common biological and cultural ancestors tens of thousands of years ago?
Undoubtedly the shared biology (proximate by the standards of biological evolution) and perhaps the shared culture (which, however, was very distant by the more rapidly changing standard of culture itself) had some effect on channeling development in certain directions rather than others. But another possibility that needs to be considered is that winnowing of less-efficient forms by selection through competition among groups may have shaped these otherwise independent historical trajectories. Some solutions to the puzzle of how to induce people to cooperate with large numbers of other unrelated people probably work better than others, and, if invented independently, might be maintained. This logic helps us understand, for example, why markets appeared alongside older reciprocal exchange systems as Pueblo peoples began to concentrate in the northern Rio Grande region of New Mexico in the A.D. 1300s (Kohler, Van Pelt, and Yap 2000). Over long enough periods, solutions that are markedly less workable may tend to be supplanted, whether through lethal intergroup competition, nonlethal cultural group selection, selective migration, or related processes (see review in Salomonsson 2010).
But such arguments are plausible only if we can show that adaptation, a concept we are borrowing from biology, has some relevance for understanding cultural behavior. This might seem a modest claim: we are not, for example, proposing that natural selection is a "universal acid" explaining all aspects of culture and its contents, as Daniel Dennett (1995) sometimes seems to do. But as we shall see, even this modest claim would be dismissed by some.
Societies are likewise in constant interaction with the environments they inhabit. They modify those environments by accident and on purpose, affecting their short-and long-term productivity. How could it not be the case that this also affects the success of the societies? One common characteristic of Neolithic societies is the rapid population growth they experience. If per capita use of resources remains constant as population grows, resources that regenerate slowly will be drawn down. This may soon require societies to move to previously uninhabited areas, if they are available—but eventually, this option will be impossible and new patterns of resource usage must be developed. Societies unable to innovate these patterns will be displaced by those that can.
The general growth of Neolithic populations also favors those groups that can effectively coordinate the largest numbers of people, since large cohesive groups can displace smaller or less cohesive groups, or resist displacement by others. These two pressures—building larger sedentary groups and not depleting the environment—are at odds with each other. This contributes to the dynamic character of the Neolithic record in most areas; in finding an effective compromise between these two opposing forces, societies are driven to a position on a metaphorical fitness landscape where they become extremely vulnerable to external perturbations such as climate change.
Eventually we would like to examine how these processes play out in Neolithic societies all over the world. (We suspect that they are completely general.) Unfortunately, there are few places where the Neolithic sequences are known well enough to make this possible in any convincing detail. In this book we analyze these social and "socionatural" processes through an extended case study set in southwestern Colorado between A.D. 600 and A.D. 1300. This is a fascinating 700 years that takes us, in its first two centuries, from the arrival of small groups of maize farmers in an almost uninhabited mesa and canyon country to the emergence of some of the Southwest's earliest and largest villages. But around 100 years later, by A.D. 900, most of the villages in our study area had disbanded and their inhabitants departed for the south or west. The remaining house holds once again lived mostly in small hamlets until about A.D. 1080, when a new wave of colonists arrived from the south, bringing a differently organized village lifeway backed by a novel, powerful political and religious system that united most of the eastern Southwest. Within 200 years this wave, too, receded, again to the south, leaving behind the famous ruins of Mesa Verde National Park and the less-well-known but more populous district that includes Canyons of the Ancients National Monument, where our work centers (Figure 1.1).
Even before the project on which we report here began in 2001, archaeologists knew more about the development of societies in this area than was known about almost any other comparable Neolithic society anywhere in the world. For that we thank generations of researchers, recently including Hayes (1964), Kane (1986), Lipe et al. (1999), Rohn (1977), Varien (1999a), and Varien and Wilshusen (2002), among many others.
Why, then, another book? The answer lies in an exciting opportunity that the National Science Foundation (NSF) presented in 2001 for a Biocomplexity in the Environment Special Competition in "coupled natural and human systems." NSF recognized that understanding how humans interacted with ecosystems over long periods required both deep interdisciplinary collaboration and modeling. They also realized that such research was not being generated by their existing programs. When we saw this call for proposals, we recognized it as providing precisely the sort of research program we had been trying to put together. We also understood that we needed help to carry out the kind and scope of research that NSF was requesting, and we assembled a team to create a research proposal that came to be known as the Village Ecodynamics Project (VEP).
Fortunately we were not starting from a blank slate. Timothy Kohler, an external professor at the Santa Fe Institute (SFI), had recently hosted a conference there on agent-based modeling (Kohler and Gumerman, eds. 2000), at which Bob Reynolds presented a paper on his research with Joyce Marcus and Kent Flannery on the role of conflict in the prehispanic emergence of chiefdoms and states in the Valley of Oaxaca (Reynolds 2000). Reynolds is nearly unique among computer scientists in having a long history of collaboration with archaeologists: complexity pioneer John Holland and archaeologist Flannery had co-chaired Reynolds's dissertation committee at the University of Michigan. By then a computer scientist at Wayne State University, Reynolds agreed to join our team as a principal investigator on the proposal, and among the many assets he brought to the collaboration was Ziad Kobti, then Reynolds's Ph.D. student. In Chapter 13 of this book, Kobti reports on VEP efforts to model local exchange among house holds in our simulations.
Given NSF's charge to understand how societies were shaped by their changing environments, and how those societies in turn altered their environments, we also needed a partner who could bring a broad understanding of humans in their landscapes. A second acquaintance from an SFI workshop, hydrologist Ken Kolm, agreed to take a leading role in this research to help us understand the interactions through time between people and water, which we thought would be especially important to model on this semiarid landscape. Kolm, then of the Colorado School of Mines, brought along his Ph.D. student Schaun Smith. In late 2001 this team drafted a successful proposal to fund what we came to call VEP I (NSF BCS-0119981). Kohler also brought a group of graduate students at Washington State University (WSU) to the team, and Varien involved the staff at the Crow Canyon Archaeological Center, especially Scott Ortman, who assembled the database of archaeological sites discussed in Chapters 2 and 14.
We have been at it ever since. As we write this in 2011, our research is supported by the NSF grant program Dynamics of Coupled Natural and Human Systems, which grew out of the special competition that funded the first phase of the VEP. VEP II is organically connected to VEP I because it has many of the same researchers and most of the same research interests. Many students from the first team, however, have now entered the professional workforce: Fumi Arakawa is embarking on an assistant professorship at New Mexico State University; Sarah Cole is president of Red River Archaeology in Dallas; Jason Cowan works as an archaeologist for Cultural Resource Consultants Inc. (CRC) in Washington state; Donna Glowacki is an assistant professor of anthropology at the University of Notre Dame; Dave Johnson is an archaeologist and a tribal liaison for the Bureau of Land Management in Arcata, California; Scott Ortman holds a dual position as the Lightfoot Fellow at Crow Canyon Archaeological Center and the Omidyar Fellow at SFI; Schaun Smith is a staff scientist in the Environmental Unit of Chevron Energy Technology Company in Houston; and Ziad Kobti is an associate professor of computer science at the University of Windsor.
Over the years we have seen the stream of research undertaken in 2001 lead to some fundamentally new ways of thinking about and seeing the past. Part of this is due to the interdisciplinary nature of our research, part is due to modeling the past using computer simulation, and part is due to amassing synthetic databases on all known archaeological sites in our study area. Together these allow us to develop "model-based approaches" (Kohler and van der Leeuw 2007) to generate and test expectations about what the past might have looked like if certain processes were dominant. For the VEP, it was a case of being in the right place at the right time. There are few areas in the world where the past environment can be reconstructed in such detail and linked so precisely to ancient subsistence practices; this reconstruction of ancient environments and subsistence practices was a fundamental aspect of the computer simulation. Further, there are few places where we could assemble so much previous archaeological research and analyze it in productive ways, though we had to develop new approaches to make that possible (Ortman et al. 2007). As a result, the VEP can use the computer simulation to generate models and evaluate them through quantitative comparisons to the archaeological data.
A SOCIONATURAL RESEARCH AGENDA
The VEP conducts socionatural research (van der Leeuw and Redman 2002); we examine the long-term interactions between humans and their environments. The network of scientists making this possible includes archaeologists, computer scientists, ecologists, an economist, geologists, and hydrologists, among others. We focused this research on an 1817 km2 study area in southwestern Colorado, in the heart of the central Mesa Verde region, one of the most densely occupied portions of the prehispanic Pueblo world. For analytical purposes we divided this area into 45,400 cells that are 200 m on each side, or 4 ha in size, and selected the period between A.D. 600 and A.D. 1300 as the time frame for our research. An important goal of the VEP is historical research that seeks to explain the development of Pueblo Indian society in this area during these seven centuries. Equally important, the VEP seeks to use what we learn about these societies to better understand the general processes that underlie human social evolution, especially during the Neolithic period, that pivotal epoch when humans first adopted domesticated food production.
Two major efforts define the VEP research. The first is an agent-based computer simulation that reconstructs past climate and environment, models how annual variation in precipitation and temperature affected productive resources, and examines how humans use these domesticated and wild resources. The agents in this computer simulation are house holds, although the simulation tracks the fortunes of each individual in these house holds as well. These virtual house holds are let loose on our reconstruction of the prehispanic landscape of southwestern Colorado in A.D. 600. For the next 700 years, the house holds farm maize, obtain drinking water, collect wood for fuel, hunt mule deer, jackrabbits, and cottontails, and—in some versions of the simulation—exchange maize and meat with each other.
The second major VEP effort has been archaeological research to summarize the ancestral Pueblo occupation of the study area. This was accomplished by constructing and analyzing a database of all known archaeological sites in our study area—about 9,000 in all—supplemented by a database of all tree-ring dates from the region. VEP archaeological research focused on the 3,176 sites determined to be habitations, including 92 sites we termed "community centers" based on their larger size, longer occupations, and distinctive architecture, which included public or civic structures. Additional research, including new fieldwork, was conducted at some of these community centers.
The broad questions about coupled natural and human systems emphasized by the VEP led us to focus on three aspects of the ancestral Pueblo occupation of the study area. First, we sought to understand how farmers located themselves and used resources in this landscape. Second, we wanted to examine the exchange of subsistence goods among house holds and whether this exchange caused house holds to aggregate into villages in certain times and places and disperse into smaller settlements during other times. Finally, we wanted to determine why our study area and the surrounding Mesa Verde region was depopulated in the late A.D. 1200s.
These general questions required us to answer other, more specific, questions. What were the population dynamics during the 700 years when the study area was occupied? Could farmers continue to grow maize in sufficient quantities during the driest and coldest years? Did domestic water supplies disappear during prolonged drought? Was the landscape depleted of wood resources during the long-term occupation of the study area? Could people sustainably meet their needs for protein by hunting deer, jackrabbits, and cottontails, or would they tend to seriously depress the number of these animals over time? How was exchange affected by the distribution of resources? What was the history of conflict in the region?
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Table of ContentsPreface and Acknowledgments
Emergence and Collapse of Early Villages in the Central Mesa Verde: An Introduction
Timothy A. Kohler and Mark D. Varien
The Study Area and the Ancestral Pueblo Occupation
Scott G. Ortman, Donna M. Glowacki, Mark D. Varien, and C. David Johnson
Low-Frequency Climate in the Mesa Verde Region: Beef Pasture Revisited
Aaron M. Wright
Simulation Model Overview
Timothy A. Kohler
Modeling Paleohydrologic System Structure and Function
Kenneth E. Kolm and Schaun M. Smith
Modeling Agricultural Productivity and Farming Effort
Timothy A. Kohler
Modeling Plant and Animal Productivity and Fuel Use
C. David Johnson and Timothy A. Kohler
Supply, Demand, Return Rates, and Resource Depression: Hunting in the Village Ecodynamics World
Jason A. Cowan, Timothy A. Kohler, C. David Johnson, Kevin Cooper, and R. Kyle Bocinsky
How Hunting Changes the VEP World, and How the VEP World Changes Hunting
R. Kyle Bocinsky, Jason A. Cowan, Timothy A. Kohler, and C. David Johnson
Exercising the Model: Assessing Changes in Settlement Location and Efficiency
Timothy A. Kohler, R. Kyle Bocinsky, Stefani Crabtree, and Ben Ford
Simulating Household Exchange with Cultural Algorithms
Tool-Stone Procurement in the Mesa Verde Core Region Through Time
Population Dynamics and Warfare in the Central Mesa Verde Region
Sarah M. Cole
Characterizing Community Center (Village) Formation in the VEP Study Area, A.D. 600-1280
Donna M. Glowacki and Scott G. Ortman
The Rise and Collapse of Villages in the Central Mesa Verde Region
Timothy A. Kohler
Notes on Contributors
What People are Saying About This
"Impressive. . . . The book shows what it means to simulate historical processes. . . . One of the best [books on historical simulation] available."Jasss Journal of Artificial Societies & Social Simulation