Unease with the inclusion of "sameness" in Owen's definition of homology characterizes a substantial part of the literature on this subject, where this term has acquired an increasingly strict metaphysical flavor. Taken for granted the existence of body features that are "the same," their existence has been explained by appealing to universal laws of form, as the product of common ancestry, or in terms of proximal causes responsible for the emergence of conserved developmental modules. However, a fundamentally different approach is possible, if we shift attention from metaphysics to epistemology. We may reword Owen's statement as follows: organs of different animals, in so far as they can be described as the same despite any difference in form and function, are called homologues. The proposed framework provides an umbrella for both the traditional, all-or-nothing concept of homology, and the less fashionable alternatives of factorial or partial homology, as well as for an extension of homology from form to function. No less attractive is the prospect to handle also ghost homologues, the body parts or organs of which there is non-objective evidence in a given clade, but can nevertheless be represented, in a description that encapsulates some of the traits observable in their extant homologue in the sister clade. Stripped of its different and constraining metaphysical explanations, homology survives as an anchor concept to which different nomadic disciplines and research agendas can be associated.
Keywords: anchor concept; comparative biology; factorial homology; ghost homology; homology of functions; nomadic discipline.
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