miércoles, 28 de marzo de 2007

The Evolutionary Species Concept

E. O. Wiley and Richard L. Mayden

An evolutionary species is an entity of organisms that maintains its identity from other such entities through time and over space and that has its own independent evolutionary fate and historical tendencies. Species are lineages, ontological individuals existing though time and bounded by speciation events.

The evolutionary species are logical individuals with origins, existence and ends. They are tokogenetic entities that function in the phylogenic system as the analog of phylogenetic entities, clades. Sexual species may show cohesion patterns such that the tokogenetic relationship among the organisms are not well correlated with, or are uncorrelated with, any hierarchical relationships that might exist among those organisms. On the other hand, asexual species have tokogenetic relationships that are similar to multicellular individual organisms in being composed of tokogenetic clone vectors descended from a single ancestor.

The evolutionary species maintain their identities, which refers to the reestablishment of the tokogenetic network when subsequent sympatry occurs between populations that had been allopatric. Particular species are the result of historical processes and then we have discovered them during the course of our research. They have independent tendencies which imply that they are free to vary and evolve independent of their sister species. They also have an evolutionary fate which means that the species are real entities and not a result of our imagination; their fate is to speciate or eventually goes extinct.

If the monophyletic groups have objective reality through time, the ancestral lineage and all descendants of that lineage also must have objective reality. The fact that we can reconstruct much of the phylogenetic histories of groups constitutes evidence that independently evolving lineages exist in nature. Another proof that such lineages do exist is derived from the fact that phylogenetic analysis becomes complicated when lineage independence is not strictly maintained.

The evolutionary species concept is the logical analog of the concept of the monophyletic group, therefore it is a strictly genealogical and non-operational concept. Lastly, all evolutionary species are comparable because they are the largest tokogenetic biological system, consequently general phenomena associated with speciation can be studied even among non-sister species.