On Reciprocal Illumination and Consilience in Biogeography

Abstract

Biogeography deals with the combined analysis of the spatial and temporal components of the evolutionary process. To this purpose, biogeographical analysis should consider two extra steps: a reciprocal illumination step, and a consilience step. Even if the traditional challenges of biogeography were successfully handled, the obtained hypothesis is not necessarily meaningful in biogeographical terms--it needs continuous test in the light of external hypotheses. For this reason, a concept analogous to Hennig's reciprocal illumination is valuable, as well as a sort of biogeographical consilience in Whewell's sense. Firstly, through the search for different classes of evidence, information useful to improve the hypothesis can be accessed via reciprocal illumination. Following, a more general hypothesis would arise through a consilience process, when the hypothesis explains phenomena not contemplated during its construction, as the distribution of other taxa or the existence (or absence) of fossils. This procedure aims to evaluate the robustness of biogeographical hypotheses as scientific theories. Such theories are reliable descriptions of how life changes its form both in space and time, putting historical biogeography close to Croizat's statement of evolution as a three dimensional phenomenon.

Reflections on the Phylogenetic Position and Generic Status of Abbott's Booby 'Papasula abbotti' (Aves, Sulidae)

“…Therefore, as pointed out by Santos and Capellari [34], cladograms can be compared against each other to find congruencies among them. The idea behind such a comparison is similar to Hennig's [1] method of 'reciprocal illumination', wherein two sorts of data are complementary to each other, and has the potential to enlighten one another.…”

“…If, for example, two (or more) cladograms are congruent in the sense of depicting the same or almost the same relationships, they have better explanatory power compared to other contradictory cladograms. On the other hand, in case of no or little congruence, then the differences should be reconciled through reanalysis of existing data and/or the analysis of new characters [34].…”

Realism in systematics through biogeographical consilience

“…Recently, Santos and Capellari (2009) described a non‐instrumentalist procedure to biogeographical analysis based on the search for biogeographical reciprocal illumination and consilience. In their words: “To be consilient, a general biogeographical hypothesis must explain phenomena not contemplated during its construction, as other taxonomic group distributions, the existence (or absence) of fossil groups in certain geological layers, and the phylogenetic relationships within other taxa with shared—at some extent—distributional patterns.…”

“…In their words: “To be consilient, a general biogeographical hypothesis must explain phenomena not contemplated during its construction, as other taxonomic group distributions, the existence (or absence) of fossil groups in certain geological layers, and the phylogenetic relationships within other taxa with shared—at some extent—distributional patterns. (…) [B]iogeographical consilience is as an evaluative criterion for the robustness of biogeographical hypotheses when considered as scientific theories, and not as simple descriptions of geographical patterns” (Santos and Capellari, 2009, p. 411). Consilience was first raised by William Whewell (1847) to designate situations in which a causal explanatory theory, initially constructed to explain a particular set of phenomena, provides an equally successful causal explanation to other kinds of phenomena, different from those considered during the construction of the theory (Fisch, 1985).…”

“…In this sense, as a consilient theory explains more than its own set of questions, it can be considered more trustable than a theory that explains only predicted or known situations. Although the consilient approach shown in Santos and Capellari (2009) is interpreted as a guideline to historical (and particularly cladistic) biogeography, the same consilient guidance could be used in the context of phylogenetic analyses to move away from the pure instrumentalism during the proposition of taxonomic groups and their relationships. This biogeographical approach, especially regarding consilient hypotheses, is a complementary perspective to previous papers concerning realism (e.g.…”