The goals of this research have been threefold. First, I wanted to explain the development and adoption of corrugated pottery in the American Southwest. Second, I aspired to move beyond the intuitive, often simplistic historical and functional explanations for corrugation proffered in the past. Finally, I hoped to contribute to the development of scientific explanation in archaeology and the social sciences generally, by using theory in its proper role as a set of concepts that supply the logical structure for both explanation and description. The theory, evidence and hypotheses presented in this dissertation indicate that I have had some success in each of these goals.

At the outset, I argued that explanations in social sciences, and archaeology in particular, have lacked the impact they have had in the natural sciences because intuitive, common sense notions have generally taken the place of theory in the social sciences. This has allowed various ideological biases and agenda to play a much larger and more detrimental role in the social sciences than in the natural sciences. To avoid this deficiency in my research on corrugated pottery, I have made explicit use of evolutionary theory to design my observations and formulate my explanations.

However, theory too is not immune to the intrusion of common sense. Consequently, I went to great lengths to try to expose and eliminate inconsistencies and intuitive biases from the evolutionary approach that I adopted for this research. This led me to develop the notion of frames of reference in which the conceptual units of evolutionary theory can have many different logically coherent and causally relevant relationships with the empirical entities under investigation. In this view, there can be many different replicators, interactors, environments, and lineages that are relevant to any given problem. The goal in formulating evolutionary explanations, then, is to identify those frames of reference that yield the most explanatory insight into the problem at hand. This was the approach I took in formulating the possible explanations for different aspects of the corrugation problem. Although the approach has been fruitful in terms of formulating hypotheses, it has been difficult to thoroughly test the various alternative explanations I have presented mainly because testing most of them required data not yet available. Consequently, the final step in determining the scientific validity of this approach and the specific explanations it spawned must await further research. In the remainder of this concluding chapter, I explore some general insights gleaned from my attempts to explain the evolution of corrugated pottery in the American Southwest, and discuss directions for future research.

Evolutionary Explanation of Corrugation: Some General Insights

Even without being able to test fully my various alternative explanations for the rise and fall of corrugated pottery, I have demonstrated clearly that the different varieties of corrugation form a lineage of common descent in the Southwest. But, common descent of what? In my hypotheses, I identify several replicators that appear to be relevant to the corrugation problem. These replicators include biological individuals and groups, the knowledge of how to make and use corrugated pottery, the meaning ascribed to corrugation, sociocultural institutions, and, to a limited extent, the corrugated pottery itself. As corrugation developed and spread, the significance or causal relevance of some of these replicators also fluctuated. However, it also appears likely that many of these replicators were active simultaneously. Each of these replicators also interacted with unique environments. The pottery interacted with production and use environments. Biological individuals and social groups interacted with one another and the physical and technological environment. The beliefs and knowledge people held about corrugated pottery interacted within a cognitive environment. Each of these replicator-interactor-environment combinations represents a different frame of reference from which to examine the corrugation problem. Although I attempted to probe the corrugation problem from several frames of reference in explanations presented in the previous chapter, I suspect that more frames of reference remain to be explored.

The various hypotheses I have formulated thus far also suggest that the rise and fall of corrugated pottery involved a mixture of drift and selection working through a variety of scales and units. This combination of multiple mechanisms and units produced a complex history that cannot be adequately captured with simple functional or historical accounts. The concepts of style and function that are frequently used by archaeologists to distinguish different kinds of variation do not appear to do justice to the actual workings of cultural change. This is because they tend to gloss important details of real evolutionary histories.

History and function are difficult to distinguish because of path dependence of particular technological forms. For example, I have demonstrated that corrugated cooking pots developed through a series of innovations and intermediate steps rather than being designed as a complete package. In addition, the innovations that ultimately led to the performance enhancements in corrugation appear to have been introduced originally for other reasons. That is, the benefits of corrugations were unintended consequences. Looking at the product of this process, such as full-body corrugated pots, and understanding the costs and benefits conferred by this technology in the context of intense use of moist cooking, we can begin to imagine other possible technologies that may have offered better solutions. For example, rather than leaving coils exposed, one could scrape smooth the interior and exterior surfaces to produce stronger coil welds, and then score the exterior surface to attain similar cooking control and durability enhancements offered by corrugation. This approach would allow the use of larger construction elements, thereby reducing the per unit production costs in comparison to a corrugated vessel. This scoring approach to producing a textured exterior surface did develop in other parts of the world, but was used only sparingly by ancestral Pueblo potters, and then never on the base of their vessels. This is primarily because exterior surface texturing began as a decorative use of exposed coils on vessel necks. Once they started down this path of leaving coils exposed, the use of substantial scoring became less and less likely or compatible.

This notion of path dependence is certainly not new (e.g., Adams 1996; Arthur 1989, 1994; Basalla 1988; Burke 1978) nor is it unique to technology, but is a feature common to all evolutionary trajectories. However, it is often ignored by purely functional accounts that frequently rely on the assumption that adaptation and decision making produce optimal solutions. This recognition of path dependence does not constitute a rejection of the explanatory significance of functional issues. An evolutionary approach accommodates and integrates both history and function in its explanatory structure. We also tend to think of path dependence as arising from a lack of theoretical and empirical knowledge. If only the ancient Pueblo potters and cooks had known what we know about physics and engineering, they would have arrived at a more efficient, perhaps even optimal, solution to the problems posed by intense boiling in ceramic vessels. However, path dependence is certainly not a feature only of primitive technologies. The logically constrained nature of innovation and the historically constrained features of selection result in historical accidents that can have significant impacts on the course of technological change. This is true regardless of our understanding of the physical or engineering principles involved. The combination of deterministic and contingent processes produce unique histories that are probably often neither optimal nor completely free of the constraints of energetic efficiency.

Directions for Future Research

Although this study has enhanced our understanding of corrugated pottery in the American Southwest, several issues require further research before we can be confident that this understanding is complete and accurate. We need to improve our knowledge of the history of corrugation both within and outside the Mesa Verde region. We need additional studies focused on documenting the production and use of utility wares in different areas of the Southwest. Additional studies are needed to document more thoroughly the engineering properties of plain and corrugated vessels. Finally, the hypotheses presented in the previous chapter need to be further developed and evaluated.

History of Corrugation

Through my analyses of utility ware collections from the Mesa Verde region and examination of published data from other areas, I have presented a sketch of the development and spread of corrugated pottery in the Southwest. I call it a sketch because we lack secure data on the timing and source of variation in corrugation techniques in many areas. The broad outline of what I have presented is probably correct, but formulating testable evolutionary hypotheses for the rise and fall of corrugation requires more than a broad outline of the changes we are trying to explain. Detailed analyses such as I performed in the Mesa Verde region should be carried out in other areas. This would allow us to date the appearance of particular variants in different areas and track their spread across the Southwest. The lack of well-dated assemblages for certain times in some areas may require the use of other dating techniques, such as thermoluminescence dating of the pottery itself, to resolve questions of chronological priority.

We may also need a more detailed understanding of variation in corrugation techniques within regions. My analyses in the Mesa Verde region produced a good temporal record of change in utility wares, but we still know very little about variation within and among settlements within the region. This kind of knowledge could help us distinguish different mechanisms, such as migration, diffusion and innovation, responsible for the introduction of new corrugation techniques.

Utility Ware Production and Use

We still have very limited secure knowledge regarding the production and use of utility wares in the Southwest. Two issues, in particular, need more thorough attention. Current evidence suggests that the organization of production and distribution of utility and painted pottery may have changed dramatically at about the same time that full-body corrugated pottery was adopted. However, this evidence is spotty and, in some cases, circumstantial. We need to expand our knowledge of utility ware production through more sourcing studies aimed at utility wares, and a greater attention to documenting direct evidence of utility ware production during new excavations. In addition, we need to document more thoroughly the relationship between the production of utility wares and painted pottery outside the Mesa Verde region. I was able to generate some intriguing evidence related to this issue in the Mesa Verde region based on published information alone. I suspect this will be true for other parts of the Southwest as well making the huge primary literature, consisting mainly site reports, a potential gold mine of information on this topic.

Regarding the use of utility wares, the evidence I generated on the intensification of use in moist cooking needs to be expanded by conducting the same analyses for additional assemblages from the Mesa Verde region and on assemblages from other areas. Studies of large samples of whole and restored utility ware vessels from well-dated and documented contexts could significantly augment analyses of sherd assemblages. It may also be useful to bring new analytical approaches, such as residue analyses, to bear on the problem. We need to know if the same pattern of change in the type and intensity of use documented for the Mesa Verde region occurred in other areas of the Southwest. I am especially curious as to whether these changes in use accompany the development and adoption of corrugation in other areas, particularly those areas in which corrugation was adopted more slowly.

Engineering Properties

The engineering analyses conducted for this study succeeded in documenting several differences and similarities in the cost and performance of Southwestern plain and corrugated utility wares. Nonetheless, I was not able to address some areas as well as I would have liked. These issues include vessel use-life, the effects of vessel size on cost and performance, and ease of handling. Both the use-life experiments and estimates of actual accumulation rates suggest that full-body corrugated pots are more durable than plain pots when used for cooking. However, the small sample of vessels included in the use-life study resulted in ambiguous and conflicting results from the strength testing. To improve our documentation of differences in vessel use-life, the number of vessels subjected to use-life experiments and the duration of use must be increased substantially. Estimating accumulation rates for utility wares for other assemblages in the Mesa Verde region and elsewhere in the Southwest can also contribute to a clearer understanding of the impacts of full-body corrugation on vessel use-life.

In my cost and performance experiments, I held vessel size constant, and used relatively small vessels to minimize the cost of experiments, which were already extremely labor and time intensive. This means that I do not have data to address how changes in vessel size may have affected the cost or performance of plain and corrugated vessels. It is possible, though I think unlikely, that differences in vessel size could affect performance and use-life due to the allometric increase in volume relative to surface area. To assess this possibility, experiments similar to the one I performed should be conducted using larger vessels more in keeping with the average size of actual Puebloan utility wares.

My studies of ease of handling were purely anecdotal, and thus the observations I made lack any real quantitative dimension. To further document potential differences in ease of handling between plain and corrugated vessels, controlled observations and experiments should be designed and carried out. These studies should measure the actual surface roughness of different kinds of corrugation, and the effects of this roughness on friction and slippage under static load. For example, a clamp could be set up to squeeze vessels around the neck at a constant pressure. Pots with different kinds of corrugation on their necks but the same in other respects could then be placed into this devise, and a substance could then be added gradually to the pot to increase its weight at a constant rate. The weight of added contents at the time of first slippage in the clap would be a measure of one aspect of ease of handling.

Further Development and Testing of Hypotheses

In presenting the hypotheses regarding various aspects of the corrugation problem in the previous chapter, I chose to employ a narrative format that emphasized the possible causal relationships of different historical contexts. In the interests of creating a readable narrative of reasonable length, I did not take the time to present the hypotheses in a more formal way. A formal treatment would involve explicitly specifying the evolutionary function (i.e., replicator, interactor, environment, population, etc.) of each of the units under discussion, and possibly expressing the proposed causal relationships in a more quantitative manner. Given the preliminary nature of much of the evidence on which the hypotheses are based, I also thought it would be premature to present formal hypotheses at this time. However, as our knowledge of the history, production and use contexts, and engineering properties of Southwestern utility ware improves, it will be important to formalize these hypotheses so that they can be evaluated with explicit empirical tests.

Further testing of the hypotheses will also require better data on several topics that are well beyond the realm of pottery. These include issues such as the extent and direction of migrations, the constitution of migrant and indigenous populations, and the existence and character of large-scale sociocultural entities. Obtaining accurate knowledge of these issues will require archaeologists to generate and synthesize data on scales much larger than we normally work. We may also need new ways to think about and document these kinds of problems. Consequently, I expect it will be a long time before we have any secure scientific explanations of the rise and fall of corrugated pottery. However, I hope that the research presented here has set us moving in the right direction.

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