Tracing homologies in an ever-changing world

Abstract

One century and half after the publication of Darwin’s Origin, Owen’s notion of homology, which implies that two organs or features under comparison can be recognized as “the same” continues to dominate current approaches to the problem of homology. Eventually, the idea that characters can “remain themselves” throughout an indefinite although obviously finite number of possible alternative states that follow one another in the course of evolution is probably based on an idealistic interpretation of how organisms evolve. If the existence of body features that are “the same” is taken as given, then the existence of homologues can be explained according to one of the following lines: (i) in terms of universal laws of form, perhaps reformulated in the language of process structuralism, or (ii) as the product of common ancestry, or (iii) in terms of proximal causes responsible for the emergence of conserved developmental modules. However, reading the history of life through the lens of evolution, it appears very problematic to describe organisms in terms of characters that, since they first showed up as evolutionary novelties, eventually remain as essentially unchanging building blocks among which we can predicate or negate homology. All traits are better interpreted as complex and ever-changing intersections of an indeterminate number of features, and of the processes shaping them in ontogeny and in phylogeny. As a consequence, a factorial or combinatorial approach to homology is suggested.

Keywords

• Evolutionary novelty
• finalism
• homology
• combinatorial
• origins