The goal of scientific explanation has proven to be a significant challenge in archaeology as well as other social sciences. During the rise of the "New Archaeology" in the 1960s, there was great optimism that archaeology could become a true science simply by adopting the methods of science, in particular the explicit formulation and testing of hypotheses (e.g., Watson et al. 1971). However, this optimism has waned considerably as archaeologists have come to recognize that scientific explanation requires far more than borrowing rituals and concepts from other well-established sciences. Currently, little agreement exists among archaeologists regarding the particular theories and methods that are most suitable for generating valid, accurate and useful scientific explanations, and numerous different approaches vie for acceptance ( Cordell 1994; Trigger 1989).

One response to this state of affairs has been to reject science, particularly its reliance on causal explanation and empirical epistemological standards, as an appropriate or effective approach to understanding the human condition. Ever since the middle part of the twentieth century when Butterfield (1957), Hanson (1958), and Kuhn (1962) argued on philosophical and historical grounds for the theory- laden nature of all observation, a school of conceptual relativism has grown to challenge the hegemonic status of science in Western society (e.g., Barnes and Bloor 1982; Collins 1985; Feyerabend 1987; Nagel 1986). Although largely ignored by practitioners of the natural sciences, this relativist position has made greater inroads into the thinking and discourse of the social and cognitive sciences. Proponents of this approach argue that science's claims for the progressive growth of more secure knowledge is merely a chimera, and that no true standards of reasoning exist allowing objective distinctions to be made between competing knowledge claims. Instead, relativists argue that change in science and other systems of knowledge occur through social and political processes, not objective evaluation. At the extreme, this form of relativism holds that anything goes, and all knowledge claims are equally valid from an evidential standpoint (Feyerabend 1975).

Among archaeologists, the conceptual relativist position has been promulgated under the rubrics of "post-processualism" and "post-modernism" ( Hodder 1983, 1984; Shanks and Tilley 1987a, 1987b). As the name implies, this view developed in opposition to positivist and empiricist perspectives that served as major influences for the processual archaeology of the 1960s and 1970s ( Binford 1968; Fritz and Plog 1970; Hill 1977; Watson et al. 1971). Proponents of the relativist position in archaeology argue that all facts are constructed, and consequently, reflect more the beliefs, motivations, and cultural milieu of the constructor than an objectively true view of the past. Ardent defenders of the processual approach have criticized the relativism of post-processual archaeologists as conceptual posturing and promoting an unnecessary and undesired politicization of archaeology ( Binford 1989; Watson 1990 ). Perhaps in response to these criticisms, but more likely as a self-initiated retreat from the edge of intellectual chaos, the hard line of conceptual relativism in archaeology has begun to soften ( Hodder 1991; Wylie 1992). However, the critique of most archaeological practice as infused with implicit ontological biases and frequently lacking objective, empirical evaluation remains firm and generally accurate ( Cordell et al. 1994 ).

If archaeologists, as well as other social scientists, are to continue pursuing the objective of scientific explanation, then we must confront the problems that prompted the valid aspects of the relativist, post-modern critique of current practice. A common theme in much of this critique is that science is not immune to the influence of the social and political climate of its practitioners as had been suggested by proponents of positivist and empiricist perspectives. Although it is true that the objective nature of science has been greatly mythologized ( Bauer 1992 ), there has still been tremendous progress in our scientific understanding of the world around us despite social and political influences ( Kitcher 1993 ). The fact that scientific practice involves a social and political component does not appear to disqualify the endeavor a priori from advancing secure and accurate knowledge. Rather, the significant differences between the natural and the social sciences lie in the conceptions of the roles and relationships between theory and measurement.

In the natural sciences, theory consists of a set of abstract concepts that specify the causal relationships and ontological status of classes of entities. Because these classes have empirical referents in the real world, both description (through measurement) and explanation (through the application of theoretical concepts) of particular cases occur within a logically coherent framework making empirical tests possible. In the social sciences, theory is frequently viewed as generalizing statements derived directly from observations ( Dunnell 1982; Willer and Willer 1974 ). One examines specific cases and explains these cases by specifying the causal or structuring relationships thought to exist among the particular observations. Because theory tends not to play the logically structuring role that it does in the natural sciences, contradictory descriptive units and explanatory concepts abound in the social sciences, and empirical tests have little or no relevance beyond particular cases. However, the structuring role played by theory in the natural sciences is not absent in the social sciences. Instead, the concepts that fill this role tend to be implicit and derived from common sense notions regarding the basic features of human nature ( Dennett 1987, 1991; Dunnell 1982 ).

Several liabilities follow directly from the intrusion of common sense in the role of theory. Common sense lacks logical coherence by its very nature as a mostly intuitive hodge-podge of ways of making sense of the world around us. The various forces that have shaped our common sense notions did not require that these notions be coherent or even rational. Rather, they only needed to succeed more often than their competitors at generating effective, and usually rapid, predictions and solutions. In fact, detailed psychological studies have demonstrated that our common sense can easily produce illogical and irrational beliefs ( Nisbett and Ross 1980; Vyse 1997 ).

These contingent and incoherent aspects of common sense also allow social and political influences to become seriously debilitating. The most common approach to explaining and predicting the actions of people around us relies on folk psychology, which invokes the intentions or agency of the actors involved ( Dennett 1984, 1987 ). With this approach, particular explanations or predictions derive mainly from introspection regarding how we would feel, believe, act, or respond given the situation, and speculation about the thoughts of others based on various behavioral clues. In fact, this sense-making approach is so deeply ingrained that it is rarely explicit. Consequently, this notion of agency also underlies most of the theoretical positions within the social sciences, either implicitly or explicitly ( Little 1991 ). When intentional explanations are derived from an implicit, common sense or folk view of agency, particular accounts tend to follow the concurrently fashionable or institutionally dominant trends in attitudes toward human motivation. Under these conditions, we learn nothing about human nature. Instead, we reify folk concepts that usually support the dominant social, political, and economic forces in society at the time, or the particular beliefs of the scholars involved.

As many of the post-processualist critics have argued (e.g., Leone et al. 1987; Shanks and Tilley 1987a ), knowledge claims by archaeologists about the past can be particularly susceptible to the intrusion of this kind of common sense, intentional explanation. The artifacts from which we make our inferences rarely impinge on our tendencies to create the past in our own image. Consequently, it is not surprising that archaeologists have grown increasingly divided over possible explanations, and even our basic goals, as the discipline has become more pluralistic and less dominated by affluent white males.

Although folk-psychological accounts function reasonably well in our daily lives, this is no reason to believe that they can form the basis of scientific explanations. Just as we have common sense notions of ourselves, we also posses such notions regarding the physical world. Folk concepts such as temperature differences between wood and metal at the same temperature, and a world composed of four basic elements (earth, fire, water, and air), although based on common and compelling sensory experiences, have been replaced by more accurate scientific concepts. In fact, most major advances in scientific understanding of nature have come at the expense of common sense notions of the way the world works ( Cromer 1993; Kitcher 1993; Wolpert 1994 ). This does not mean that common sense intentional explanations of human behavior are necessarily wrong. However, the history of science should make us suspicious of notions derived from folk psychology, and inspire us to evaluate these notions from both logical and empirical standpoints, as well as to make them consistent with other knowledge, particularly from the natural sciences.

The philosopher Wilfred Sellars (1962), in his now classic essay "Philosophy and the Scientific Image of Man," describes what he sees as fundamental metaphysical differences between the manifest (folk) and scientific images of the world. In the manifest image, essential intentions and motivations underlie and cause human actions. Thus, explanation under the manifest image is teleological or goal directed, and it is the goals of the actors that are causal. In the scientific image, teleology and the language of intentions is abandoned in favor of a mechanistic view in which cause lies outside the phenomena under investigation. Although disciplines such as physics and chemistry adopted a scientific image long ago, the manifest image remains the dominant if not exclusive position in the social sciences. The persistence of the manifest image in the social sciences derives at least in part from constant exposure to our own and other people's common sense reasoning and rationalizations, and resistance to objectifying or dehumanizing people by questioning the explanatory validity of the products of their common sense reasoning.

More recently, the philosopher Daniel Dennett (1987, 1995) has argued that the intentional stance of the manifest image also characterizes evolutionary explanations in biology although the intention is "free floating" rather than a quality of individual organisms. Thus, although Dennett, among others ( Churchland 1981; Quine 1960; Stich 1983 ), has questioned the veracity and utility of folk-psychological concepts for explaining human thought and actions, he has defended intention as an important principle in scientific explanation. From this perspective, the persistence of the manifest image among social scientists may also stem from the validity of some aspects of an intentional approach to explaining human behavior. However, even if parts of the manifest image have scientific validity, there is no guarantee that any specific common sense beliefs about the nature of human intentions are accurate or provide a useful basis for explanation.

Although it is not yet clear which concepts will prove most useful in explaining human behavior, it is abundantly evident that we must replace implicit, common sense notions with explicit theory if we are to move closer to the goal of scientific explanation in archaeology and other social sciences. By emphasizing the problems created by the intrusion of common sense into the role of theory, I do not mean to imply that there is no theory in the social sciences. A wide variety of theoretical and pseudo-theoretical positions exist within the social sciences ( Little 1991; Trigger 1998 ), but, as yet, none has successfully escaped the influence of folk psychology, or ontological quandaries engendered by borrowing theory from other areas of science.

As the biologist Richard Lewontin (1974:8 ) points out for the case of population genetics, constructing viable scientific theory is no simple task. One must move back and forth between building conceptual and empirical units with the goal of improving the fit between them so that they form a logically coherent and empirically valid network of causation through explicit processes and mechanisms. This iterative process is difficult because constructing valid concepts often depends on having a set of valid empirical units, which, in turn, depend on concepts for determining their relevance. Such contradictions cannot be resolved easily in one short burst of theory and unit construction. Instead, we must be content to work through a process of trial, error, and synthesis to build a more scientific approach to explanation of sociocultural phenomena.

This dissertation presents an attempt to further the growth of scientific explanation in archaeology by building, applying, and beginning to test explanations derived from Darwinian evolutionary theory within the context of a specific empirical problem. The empirical problem I attempt to explain is the development of the roughly textured corrugated pottery from plain antecedents between the eighth and eleventh centuries AD in the Colorado Plateau region of the American Southwest. Because of the unusual and visually striking aspects of corrugated pottery, there have been numerous attempts, spread across more than 100 years of Southwestern archaeology, to describe and explain its adoption among the ancestors of the modern Pueblo Indians. In the next chapter, I expound upon this problem in more detail by presenting a brief description of the changes in pottery technology involved, and discussing the history of explanations for the development of corrugation. This history of explanatory attempts documents how unevaluated, implicit notions regarding human nature have intruded into and compromised previous accounts of the change from plain to corrugated pottery.

In Chapter 3, I turn to the task of building the conceptual aspects of evolutionary theory so that this body of theory can be brought to bear on the corrugation problem. Although Darwinian evolutionary theory was developed in biology, it is no longer strictly a biological theory. Attempts to develop the notion of "universal Darwinism" and to apply evolutionary theory to problems outside of biology have demonstrated that evolution is an algorithmic process that occurs when ever the conditions of inheritance, variation, and competition are met ( Bradie 1994; Calvin 1997; Cziko 1995; Dawkins 1978, 1982; Dennett 1995; Edelman 1987; Holland 1992; Hull 1988b; Koza 1992; Lewontin 1970; Smolin 1995 ). Despite the progress made in generalizing evolutionary theory beyond its biological roots, considerable disagreement exists among archaeologists and other social scientists regarding the most appropriate way to apply evolutionary theory to sociocultural phenomena. Consequently, I devote most of Chapter 3 to addressing these areas of discord, and developing concepts that I hope will lead to a more unified evolutionary approach.

However, formulating coherent concepts is just one side of the process of building sufficient scientific theory. The theory must also have some empirical referents among the phenomena under investigation, in this case, the archaeological record of artifacts and their spatial and temporal relationships. In Chapter 4, I present a research design for implementing an evolutionary approach to explaining the rise of corrugated pottery. Chapter 4 includes a discussion of the data requirements, the approach I take to formulating and testing specific hypotheses, and a description of the pottery collections analyzed for this study. In addition to describing the specific assemblages I chose to analyze, this latter section includes a discussion and justification of my selection criteria, and an evaluation of possible biases in the data generated from my analyses of these collections.

Chapters 5 through 7 present the methods and results of the various studies performed for this research. Chapter 5 focuses on the development and spread of corrugation in the American Southwest. Based on my analyses of utility ware collections, I detail the sequence of technological changes that occurred during the development of corrugation in the Mesa Verde region of southwestern Colorado. Then I draw on published data to reconstruct the spread of these innovations into different areas of the Southwest. In Chapter 6, I examine evidence for the production and use of Southwestern utility wares as potentially important aspects of the environment in which corrugation developed. Again, the data for this chapter come from my analyses of pottery collections and published sources. Chapter 7 centers on determining whether any engineering (cost and performance) differences exist between plain and corrugated vessels. The data in this Chapter are based mainly on a series of experiments I performed with modern replicas of the different kinds of pottery.

With this theoretical and empirical groundwork, I turn to the task of explaining the rise and fall of corrugated pottery in Chapter 8. My goal in this chapter is to synthesize what we know about the history of corrugated pottery and the contexts in which the different kinds of corrugation developed, spread, and disappeared. In the context of this synthesis, I present a variety of possible explanations for different aspects of the corrugation problem that are compatible with the evolutionary approach adopted for this study. I intend these hypotheses to be an initial step toward explanation and not a final word. Although I attempt to evaluate the hypotheses when possible, thorough testing must wait until we have better data on several topics and more complete and formal development of the hypotheses. These additional data requirements and steps in hypothesis formulation specify clear directions for future research. I discuss several of these future research directions in Chapter 9 after considering some general insights derived from this study into the corrugation problem and the evolutionary explanation of technological change.

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