Concept of Species - Morphological, Biological and Phylogenetic

Species is the fundamental unit of taxonomic classification - a concept going back to Plato's Greek notion of 'eidos', and defined by Stebbins (1977) as the basic unit of the evolutionary process. A species is a group of organisms that (1) closely resemble each other more than they resemble other populations, (2) descend from a common ancestor, (3) in sexually reproducing organisms, interbreed freely in nature and produce fertile offspring, (4) in asexually reproducing organisms, are identified purely by morphological resemblance, and (5) in fossil organisms, are identified by morphological and anatomical resemblance.

Species concepts fall into two general groups: those emphasising the PROCESS of evolution (which maintains a species as a unit and can drive divergence/speciation) and those emphasising the PRODUCT of evolution. This gives three named types of species. A Morphological (Taxonomic) species groups individuals that are similar in one or more features and different from other such groups, defined without any knowledge of phylogenetic history, gene flow or reproductive mechanisms. A Biological (Isolation) species, per Ernst Mayr (1963), is 'groups of populations that interbreed and are reproductively isolated from other such groups in nature' - this is the process-of-evolution concept. A Phylogenetic species, develop …