Speciation and Hybridization

Abstract

With regard to sexually-reproducing organisms, several “species concepts” have been advanced (Box 7.1). Most of these entail the perception of conspecific populations as a field for gene recombination—in other words, as an extended reproductive community within which genetic exchange potentially takes place. For example, under the popular “biological species concept” (BSC) championed by Dobzhansky (1937), species are characterized as “groups of actually or potentially interbreeding natural populations which are reproductively isolated from other such groups” (Mayr, 1963). Many authors have expressed sentiments on the BSC similar to those of Ayala (1976b): “among cladogenetic processes, the most decisive one is speciation—the process by which one species splits into two or more .. Species are, therefore, independent evolutionary units. Adaptive changes occurring in an individual or population may be extended to all members of the species by natural selection; they cannot, however, be passed on to different species.” Thus, under the BSC and related concepts, species are perceived as biological and evolutionary entities that are far more meaningful and less arbitrary than other taxonomic categories such as subspecies, genera, or orders (Dobzhansky, 1970). Nonetheless, several complications can attend the application of BSC principles.