Leonard Finkelman (Linfield College)
Nearly all species that have ever evolved are now extinct. Despite its ubiquity, theorists have generally neglected to clarify the concept (Raup 1992). In the most extensive conceptual analysis currently available, Delord (2007) distinguishes three senses by which the term “extinct” may be predicated of a taxon. A taxon is “functionally” extinct if the taxon no longer contributes to ecosystem processes; a taxon is “demographically” extinct if the taxon has no living members; a taxon is “finally” extinct if the information necessary to propagate the taxon vanishes. Ambiguity between these senses contributes to confusions and inconsistencies in discussions of extinction (Siipi & Finkelman 2017). I offer a more general account that reconciles Delord’s three senses of the term “extinct” by treating the term as a relation rather than a single-place predicate: a taxon is extinct if and only if the probability of any observer’s encountering the species approaches zero. To treat extinction as a relation in this way follows from methods for diagnosing precise extinction dates through extrapolation from “sighting record” frequencies (Solow 1993; Bradshaw, et al. 2012). By this account, Delord’s three senses of extinction mark different levels of significance in the sighting probability’s approach to zero. This has the advantages of integrating all discussions of extinction under a single unitary concept and of maintaining consistent and unambiguous use of the term, even as technological advances alter the scope of extinction.
