abstract: In this article, we consider the tension between unification and pluralism in biological theory. We begin with a consideration of historical efforts to establish a unified understanding of evolution in the neo-Darwinian synthesis. The fragmentation of the evolutionary synthesis by molecular evolution suggests the limitations of the general unificationist ideal for biology but not necessarily for integrating explanations. In the second half of this article, we defend a specific variety of pluralism that allows for the integration required for explanations of complex phenomena without unification on a large scale. (..) behavior depends on multiple levels of organization and multiple causal components. Additionally, ever since Niko Tinbergen’s articulation of four questions and Ernst Mayr’s distinction between ultimate and proximate causes, there is general recognition of multiple levels of analysis (function, cause, development, evolution) or questions (why and how) that can be brought to bear to explain a biological property or behavior. (..) tension between unification and pluralism in biological theory (..) developing consensus about the primacy of natural selection (..) but not all molecular changes had been subject to natural selection (Zuckerkandl and Pauling 1965; Dietrich 1994) (..) importance of neutral mutations and random drift (..) Evolution at the molecular level is marked by a significant role for random drift but does not exclude natural selection. In contrast, evolution at the morphological level is marked by the predominance of natural selection. (..) Martin Kreitman claims that "Kimura’s theory of neutrally evolving mutations is the backbone for evolutionary analysis of DNA sequence variation and change" because a "substantial fraction" of the genome is best modeled as selectively neutral, because selective neutrality is a "useful null hypothesis," and because "statistical analysis of (potentially) neutral variation in a gene (or other region of the genome) can be informative about selection acting at linked sites" (Kreitman 2000, pp. 541-542). (..) Rather than seek a new unifying theory of evolution, however, current evolutionary biologists seem to accept multiple causal processes and types of explanations offered for evolutionary phenomena at the molecular and morphological levels. The result is explanatory and methodological pluralism in contemporary evolutionary biology. (..) What we defend here is integrative pluralism, a view of the diversity of scientific explanations that endorses close study and modeling of different causes and different levels of organization but calls for integration of the multiple accounts in the explanation of concrete phenomena. (..) multiple factors in interaction are responsible for... (..) Thus, pluralism in the explanations of some feature of the biological world might refer to competing hypotheses (endemic vs. novel in a particular population) or multiple contributing causes (climate change and disease acting jointly) or multiple constellations of causes (climate change and disease in one population and disease and nonnative species in another) acting in different contexts or at different times. (..) Tinbergen (1963), in an influential article, outlined a four-part classification of questions one might ask of a biological phenomenon. (..) > Sherman (1988): 4 levels of analysis: levels of evolutionary origin, current reproductive function, ontogeny, and mechanism. (..) The pluralism of levels of analysis identifies strata in which explanations do not directly compete with each other; however, an isolationist stance with regard to these levels would be mistaken. (..) By modeling each individual causal factor, one can discover its possible contribution to a complex effect. But only by integrating multiple causes in multiple combinations can one begin to detect the actual causal history leading to the decline of, say, western toads in Oregon as compared with toads occurring in Colorado (Blaustein et al. 1998). (..) A unified theory would promise that a single type of causal factor (drift or selection) or at least a single model of multiple causal factors (UV radiation plus introduced species) would explain all the biological phenomena we investigate. But contingency, context sensitivity, and nonlinear interaction among contributing causes preclude the success of these types of unification. The "levels of analysis" framework describes the territory of pluralistic investigations, but it is only by integration of the multiple levels and multiple causes, including attention to the diverse contexts in which they occur, that satisfactory explanations can be generated. |