biology: species pluralism > taxonomy & why diversity (evolutionary biology) (..) disagreement over the nature (and definition) of species (..) some hold this for an unfinished debate still to be settled, others hold that there is no common and distinctive attribute of all species taxa, thus the species category is heterogeneous (..) The first group of authors advocate species monism, the second promote species pluralism. (..) I offer an alternative brand of species pluralism (..) species pluralism - Mayr: interbreeding approach (..) Patterson: mate recognition concept (..) Van Valen: ecological approach (selective environmental forces) (..) Mishler: Phylogenetic approach (propinquity of descent) (some monophyletic taxa are ranked as species because their organisms interbreed or share common ecological and developmental factors Other monophyletic taxa are ranked as species on the basis of morphological gaps between their organisms and those of other taxa) (..) they all assume that species are lineages. (..) Different taxonomies are incompatible in that they often classify the same organisms into different lineages. (..) I argue for a plurality of equally legitimate though incompatible taxonomies of the organic world. (..) The forces of evolution segment the single genealogical tree into a number of different types of lineages, often causing the same organisms to belong to more than one type of lineage. (..) The forces of evolution segment the tree of life into a plurality of incompatible taxonomies. (..) we must study the various types of theoretically important lineages in the world. No particular type of lineage is prior in that study. (..) The plurality of types of lineages at the macroscopic level is just transferred to a plurality of types of genetic factors at the microscopic level. The attempt to find a common genetic factor that unifies the three types of lineages in question fails. (..) The term "species" has outlived its usefulness and should be replaced by terms that more accurately describe the different types of lineages that biologists refer to as "species". For example, Grant (1981) suggests using the terms "biospecies" and "ecospecies" for the lineages picked out by the interbreeding and ecological approaches. Add to these the term "phylospecies". (..) Accordinglall the form of species pluralism advocated here "eliminative pluralism": Eliminate the term "species" and replace it with a plurality of more accurate terms. (..) Eliminative pluralism assumes that there is one genealogical tree of life, but that tree is segmented by different evolutionary forces into different lineages (often with the same organisms belonging to more than one type of lineage). As a result, the tree of life is segmented into different taxonomies (..) taxonomies of different aspects of the tree of life. (..) Against the 'no criteria' ('anything goes') objects ME presents criteria (..) The three taxonomic approaches considered here (the interbreeding, ecological, and phylogenetic) contain motivating principles that cite the causal process primarily responsible for the type of lineages in question. (..) First, the motivating principles of a taxonomic approach should be empirically testable. (..) Second, the sorting principles of a taxonomic approach should produce a single internally consistent taxonomy. (..) Third, the motivating principles of a taxonomic approach should be consistent with well-established hypotheses in other scientific disciplines. (..) Fourth, the motivating principles of a taxonomic approach should be consistent with and derivable from the tenets of the theory for which the taxonomy is produced. (..) This (incomplete) list of criteria does a good job at ruling out paradigm illegitimate taxonomic approaches, because they violate the criteria, like the creationist taxonomic approach, idealistic morphology (Goethe, Owen - typological thinking), phenetic approaches (Hull, Ridley). (..) Interbreeding, ecological and phylogenetic approaches do satisfy the criteria. (..) The empirical world ultimately decides whether pluralism within a particular discipline is appropriate. (..) A number of philosophers and biologists (Ruse 1969, 1987; Dupre 1981; Mishler and Donoghue 1982 Kitcher 1984a, 1984b, 1987; Mishler and Brandon 1987) have already advocated species pluralism. (..) Some species taxa owe their existence to reproductive factors, other species taxa are the result of ecological forces, still others are due to homeostatic inertia. (..) If species taxa, or any taxa, are to evolve, they must form historically connected entities. (..) In summary, Dupre's and Kitcher's forms of pluralism are too liberal, while the forms advocated by Mishler, Donoghue and Brandon, and Ruse are not liberal enough. Eliminative pluralism charts a middle course between these forms of pluralism. It acknowledges that the forces of evolution create different types of basal taxa. It also recognizes that these different types of taxa give rise to taxonomies that cross classify the organic world. Eliminative pluralism, however, is prudent enough to place constraints on pluralism: Only taxonomic approaches that satisfy the criteria suggested in section 3 are allowed into the store of legitimate taxonomic approaches. Moreover, eliminative pluralism avoids ambiguity by designating different types of taxa with different terms, and it preserves consistency by requiring that taxonomic approaches be internally consistent. |