Evolutionary Theory: Bridging the Contributions of Evolutionary Ecology and Evolutionary Archaeology

Theory is the fundamental component of any scientific discipline that attempts to explain cause and effect relationships. According to Futuyma, "the theory of evolution is a body of interconnected statements about natural selection and the other processes that are thought to cause evolution...the historic reality of evolution is not a theory. It is a fact." (1986:15). The evolution of human kind is also a fact, and there is no logical reason why human behavior should not be studied from a Darwinian perspective.

Ernst Mayr, an eminent philosopher and evolutionary biologist, has distinguished proximate cause from ultimate cause for evolutionary processes of life forms. The discovery of proximate cause is the goal of the functionalist biologist-"What makes behavior happen at a given moment?"-whereas the goal of the evolutionary biologist is to discover the ultimate cause-"Why did the trait come about?" Like biology, anthropology falls into two largely separate fields-functional anthropology and evolutionary anthropology. These two fields overlap, of course, but they are distinct. The functional anthropologist is interested in the structural elements of culture, from marriage rules within a particular society to an understanding of universal laws of incest. The questions that guide functionalist researchers focus on how a cultural characteristic operates, how it functions (functional causation). The evolutionary anthropologist, on the other hand, is interested in why some cultural trait evolved with the focus on historical process and a desire to know what caused change in cultural traits (ultimate causation). Each approach has its particular merits and both contribute to anthropology. However, the latter is the only approach which can account for change in the evolutionary trajectory of prehistoric cultures. In other words, without an historic reference, it is impossible to understand evolution and, therefore, culture change.

To move forward as a science, anthropology must focus on careful consideration of terms and concepts. The lynch pin in biological evolutionary theory is the concept of natural selection first advanced by Darwin and independently by Wallace more than one hundred years ago. In evolutionary biology, natural selection is defined as "a statistical measure of the difference in survival or reproduction among entities that differ in one or more characteristics. Selection is not caused by differential survival and reproduction; it is differential survival and reproduction, and no more" (Futuyma 1986:150). Whenever phenotypes differ in fitness, natural selection will operate. Natural selection is a process rather than a force, and models of cultural evolution should be descriptions of evolutionary processes.

The effort to apply an authentic Darwinian evolutionary theory in American archaeology has developed around the work of Dunnell (1978, 1980; also see Graves and Ladefoged 1995; Leonard and Jones 1987; Neff 1992; O'Brien and Holland 1990; Rindos 1984). Several cultural anthropologists have also advocated a Darwinian approach to the study of human behavior (Rambo 1991, Winterhalder and Smith 1992, Bettinger 1991, Dunnell 1980, among others). Others including Winterhalder, Smith, and Boone have argued strongly for the merits of Evolutionary Ecology in the study of cultural process. Much of my early work is indeed based upon the approach they advocate. Indeed, the research that I have published is significantly derived from their arguments. My present approach attempts to bridge the contributions of Selectionist Archaeology with Evolutionary Ecology. Specifically, I have focused on conspicuous consumption as reflected in the evolutionary trajectories of prehistoric societies from the American Southwest, Ireland, and Japan.

Evolutionary archaeology needs methods for recognizing how selective retention of cultural variation shaped the archaeological record. One approach that has not yet been exploited fully is to derive adaptive hypotheses from evolutionary design arguments, then to test the hypotheses' predictions by comparing two or more segments of the archaeological record. In order to encourage further development of comparative methods, we discuss aspects of their application within evolutionary archaeology in this paper. We also present an example in which comparative observations are used to test a hypothesis about the evolution of local productive specialization and circulation of materials through space.

Two recent developments in archaeology are brought together in my work. First, theoreticians have begun to argue that the archaeological record should be viewed as the product of selection-driven evolution. Second, tree-ring research has produced a highly detailed history of climate for a large area of the northern Southwest and California. We view the record of climatic oscillations and extreme events as a record of the strength of selection favoring stabilization of specialized agricultural strategies in the arid northern Southwest and a marine economy in Coastal California. My students and I have developed experiments with computer simulations of demographic factors, climatic reconstructions, and settlement data, and we believe this will be an important area for future research regarding evolutionary processes. Much of my recent work has been directed towards explaining the evolution and construction of large monuments in Northern Ireland and for Kofun Mounds in Japan.