Concept of species historical
If we were to live in a stationary biological world, in which species would be invariable and each of them would be the product of an individual act of creation, without regard to whether through the action of supernatural forces or natural processes, the number of species would correspond to the number of these unique events. As every formation of a species would be a distinct event, the individual species would necessarily be distinct and it would not be necessary to further separately investigate the phenomenon of the existence of species. However, all the available data indicate that we are not living in a stationary biological world and that species do not emerge independently of one another. To the contrary, it is apparent that they are formed in the closest possible interdependence, that a species is formed from some other species. Under these circumstances, the existence of relatively sharp boundaries between species is a rather unexpected phenomenon which deserves a separate explanation. The historical concept of species offers one of the possible explanations for the existence of distinct species in a nonstationary world.
The historical explanation can consist, for example, in that the development of each species is characterized, for some reason, by the alternation of periods of evolutionary plasticity with long periods of evolutionary stasis, during which the species does not change even under the action of selection pressures (Eldredge & Gould 1972). Thus, the traits of the individual species would reflect the conditions that happened to prevail at the time when the particular species was evolutionarily plastic, i.e. most likely at the time and place of its formation (Flegr 1998, Flegr 2010). Under these conditions, the differences amongst the individual species would not be able to be blurred and obscured.
Another historical explanation of the existence of species in a nonstationary world could be based on the phenotype multidimensionality of living organisms. Every biological property of an organism can be considered to be a dimension in the multidimensional phenotype space. Compared to space with few dimensions, there is much lesser probability in such a multidimensional space that two individuals (for example two species) would accidentally meet, even if they are only a few steps (a few mutations) apart. There are so many directions in which individuals only one step apart can set out that it is highly improbable that they would run into each other in the future. Thus, even though the phenotype spectra of the individual species continue to expand in a multidimensional space, it is almost impossible for the two species to coalesce at some time. Thus, once formed, the species retain their distinctiveness for ever. However, this is a result of the fact that, compared with the number of evolutionary pathways that they can follow in a multidimensional phenotype space, the number of species is so small that it is highly improbable that phenotype variants would occur amongst them that would lie at the borderline between two existing species. For example, if phenotypes were to differ only in a few traits, the situation would be completely different and the phenotype spectra of the individual species could easily intersect as a consequence of mutations or through the effect of mutations and selection – on their unique pathways in evolutionary history, the various species would occasionally meet at a single place in the phenotype space.