Environmental Variables and the Fundamental Nature of Hearing

Abstract

Comparative morphologists, physiologists, and neuroethologists (including the authors of this chapter) make observations at the level of phenotypes. It is natural for them to assume that observed phenotypic traits have been sculpted by evolution and therefore, somehow, have increased the fitnesses of the organisms in which they occur. Inferences about the pathways of evolution typically are drawn from formal or informal cladograms (Manley and Clack, Chapter 1, section 1, and Fig. 1.1; Ladich and Popper, Chapter 4, Fig. 4.1; Clack and Allin, Chapter 5, Fig. 5.1). In the past, such cladograms were based on morphological relationships. This is still the case for species long extinct, but for living species they now are based more and more on molecular relationships (e.g., see Gleich et al., Chapter 8, section 2). The inferences represented by cladograms surely will be strengthened greatly when investigators finally are able to relate them directly to underlying changes in genotype—to the genetic networks that through development give rise to the observed morphological, physiological, and behavioral traits (e.g., see Coffin et al., Chapter 3, section 5; Grothe et al., Chapter 10, section 2). No matter how strong one believes the inferences about evolutionary paths have become, however, one is left with uncertainty regarding the selective pressures and physical constraints that resulted in the taking of those paths, and the ways in which the phenotypic features associated with those pathways resolved those pressures and accommodated those constraints.