Nature and Formulation of Biogeographical Hypotheses

All biogeographical studies seem to pass through three main phases: an empirical or descriptive phase, a narrative phase, and an analytical phase, the last two being the true subject matter of explanatory historical biogeography. Narrative explanations are more or less inductively based and differ from the usual covering law models of explanation in that it is the particular circumstances in the form of an historical narrative that bear the explanatory load. Much biogeographical thinking is of this nature and the hypotheses so formulated suffer from their lack of predictive power and their basic untestability—usually they cannot be falsified and a preference between competing narrative hypotheses cannot be established on logical grounds. Examples of such hypotheses are given. The best biogeographical hypotheses are those that follow the hypothetico-deductive model and an example of how this may be done is provided. A phylogenetic systematic background is essential. Rigorously formulated hypotheses must have explanatory power, internal consistency, predictive power, and potential for falsification. Our aim should be to make our biogeographical hypotheses fit these requirements for only then will we begin to understand the history underlying modern distribution patterns. Biogeography; Inductive and Deductive Methods; Dispersal.