Historical Biogeography and Earth History: Perspectives for a Future Synthesis

Abstract

to our rapidly changing knowledge of earth history. While we can applaud the recent advances in biogeography, it is questionable whether we should be overly optimistic about obtaining a synthesis of the geographical history of plants and animals on the one hand and earth history on the other. I say this not because a synthesis is impossible, but because a synthesis will only be produced when the majority of workers reach some general agreement on the theoretical bases for reconstructing the historical biogeography of organisms. The reason for this statement is simple-observations are theory-laden. Indeed, individual theoretical biases-some of which we may not be consciously aware-determine the kinds of data we collect and thus the manner in which we order those data. If biogeographers differ in their theoretical approaches, then it can be expected that the observations are likely to differ as well as the interpretations. That this is a major problem in biogeography today is easily demonstrated by comparing the papers of Darlington, Brundin, and others among zoologists, and Thorne, Smith, Raven, Axelrod, Croizat, or van Steenis among botanists. I believe most biogeographers would subscribe to the belief that the biotic and geologic worlds have evolved together, and that major distributional patterns of both plants and animals should be similar to each other and relate to major historical changes in geography and climate in a parallel manner. If this is true, then a synthesis would appear possible, and it would seem useful to begin an examination of the factors necessary to affect it. The purpose of this paper is, first, to examine the various theoretical approaches to historical biogeography and attempt to resolve some of the conflicts among them, and second, to outline several biogeographical patterns in which the distributional history of plants and animals seems consistent with earth history. One of the themes of this paper is that a lack of theoretical perspective has prevented us from seeing some of these common patterns. It is not my purpose to provide the synthesis I have been talking about; that would take far more space than is available here. Rather, I wish to discuss ideas that might facilitate zoologists and botanists alike finding some common ground in the analysis of historical biogeography.