<P> A typological species is a group of organisms in which individuals conform to certain fixed properties (a type), so that even pre-literate people often recognise the same taxon as do modern taxonomists . The clusters of variations or phenotypes within specimens (such as longer or shorter tails) would differentiate the species . This method was used as a "classical" method of determining species, such as with Linnaeus early in evolutionary theory . However, different phenotypes are not necessarily different species (e.g. a four - winged Drosophila born to a two - winged mother is not a different species). Species named in this manner are called morphospecies . </P> <P> In the 1970s, Robert R. Sokal, Theodore J. Crovello and Peter Sneath proposed a variation on this, a phenetic species, defined as a set of organisms with a similar phenotype to each other, but a different phenotype from other sets of organisms . It differs from the morphological species concept in including a numerical measure of distance or similarity to cluster entities based on multivariate comparisons of a reasonably large number of phenotypic traits . </P> <P> A mate - recognition species is a group of sexually reproducing organisms that recognize one another as potential mates . Expanding on this to allow for post-mating isolation, a cohesion species is the most inclusive population of individuals having the potential for phenotypic cohesion through intrinsic cohesion mechanisms; no matter whether populations can hybridize successfully, they are still distinct cohesion species if the amount of hybridization is insufficient to completely mix their respective gene pools . A further development of the recognition concept is provided by the biosemiotic concept of species . </P> <P> In microbiology, genes can move freely even between distantly related bacteria, possibly extending to the whole bacterial domain . As a rule of thumb, microbiologists have assumed that kinds of Bacteria or Archaea with 16S ribosomal RNA gene sequences more similar than 97% to each other need to be checked by DNA - DNA hybridisation to decide if they belong to the same species or not . This concept was narrowed in 2006 to a similarity of 98.7% . </P>

The evolutionary history of a species or group of species is called