Species concepts and speciation

Abstract

Some of the recent literature on species concepts and speciation is reviewed. It is evident that there is no single precise and objective definition of the species which is universally acceptable and applicable. Rather than trying to solve the species problem by searching for more definitions or separating the category of nomenclatural taxonomy from that of experimental research, it is suggested that it would be preferable to recognize and indeed stress that not all species are of the same kind. Different sorts of species should be recognized and understood in relation to different inherent characteristics and different strategies of evolution. We should thus recognize palaeospecies, morphospecies, sibling species, ring species, polytypic species, biospecies, introgressed species, hybrid species, compilospecies, agamospecies, gynogenetic species, and so on. It ought to be possible to devise a scheme for designating these and handling them then in a systematic manner.With reference to speciation, it is concluded that no longer should we stress that gradual allopatric speciation is the only or indeed main mode of speciation in animals. We should encompass also the concepts of quantum speciation, gradual sympatric speciation, instant speciation, and speciation by hybridization and polyploidy. There is now experimental evidence to show that these are theoretically possible. However, it is as well to remember that, to date, speciation by hybridization and polyploidy is the only proven method.As noted by many previous authors, there is no single mode of speciation. The process in different groups of animals is liable to be radically different. Further, even in the same family or genus, there is no reason to believe that the mode of speciation will be constant.