Morphological species, biological species or evolutionary species

Principal concepts of the species : morphological, biological and evolutionary

morphological species The morphological species the morphological notion of the species is often regarded as a variation of the concept of the typical species consisting in joining together in a species of the individuals having of the character morphological similar. It is not the case, because it is often a practical definition. Thus Darwin, any evolutionist who it was, had a morphological approach of the species since it wrote in 1859: “the term of species is given arbitrarily for practical reasons to a resembling itself group of individuals.

Charles Darwin (1809-1882) whose bicentenary of the birth is celebrated in 2009 is the father of the theory of the evolution of the species.

Morphology is still the most common method of identification of the species: the flora, the monographs call upon morphological criteria.

Cronquist (1968) gives also its morphological definition of the species: the species are more the small groups which are distinct in a way logical and repeated and recognizable by normal means. Is it advisable to wonder what Cronquist by “normal means heard” (binocular magnifying glasses, magnifying glasses, microscopes)?

Certain authors underlined the limits of the morphological concept. Thus, it is not rare to note morphological differences between forms youthful and adult or female and male (sexual dimorphism). Certain sympatric species (alive in the same place) can be very close morphologiquement without never hybrider (sibling species). Whereas, initially, they were often regarded as only one species, they remain separated by pre-zygotiques or post-zygotic barriers (before or after fecundation): for example, periods of flowering or anthesis (before the maturation of cheesecloth different.

The biological species

Morphology not being thus the only factor to be considered, a higher bond is then necessary: the family tie, making it possible to lead to the traditional concept of species has is enough during very a long time. Thus, according to Illiger (1800, in Cuénot, 1936): the species is the whole of the beings which give between them fertile products; according to Remane (1927), the species is a reproductive community which continues itself naturally with a constant fruitfulness. Thus to the same species the individuals morphologiquement similar and interféconds belong.

According to Mayr (1942), the species is a group of individuals having potential or real faculty to cross, separately other groups. Some reproached Mayr a nonevolutionary definition of the species. The author refutes this argument by specifying that the evolution of the species being gathered data it does not have to be put forward in its definition.

In the biological concept, the species are isolated from/to each other by barriers of reproduction preventing the production of too a large number of disharmonieuses incompatible gene combinations. These barriers are intrinsic, since related to the population considered: geographical insulation as well as the intervention of the man cannot thus be qualified barriers of reproduction in the biological design of the species.

According to Mayr (1996), the biological design of the species admits also certain passages (“escapes”) of genes from one species to another; however, being different, they will never amalgamate completely; a species being characterized by a common gene pool. Mayr recognizes that the biological design of the species does not apply to the species being propagated by vegetative multiplication. According to him, such species do not require that their genotype is protected by barriers from reproduction. In all the cases, to thus define a species in asexual multiplication, a mono population or poly-clonale, does not raise difficulties.

The evolutionary species

The concept of evolutionary species appeared more recently. According to Simpson (1961), the species is a chalk-lining of populations (ancestral and downward populations) evolving separately of the others and having its own unit role and its own evolutionary tendencies”.

For Wiley (1978), it is a chalk-lining simple who safeguards his identity of other chalk-linings and who has his own evolutionary tendencies and his own historical destiny. For their defenders, these definitions make it possible to take into account the species with asexual multiplication not considered in the biological concept of the species.

However, these definitions are strongly criticized by Mayr (1996): according to him, the comprehensible criterion of separation of the species in the biological concept (reproductive insulation) is replaced by a very vague criterion of “maintenance of identity”, “evolutionary tendencies” (which are and how to define them?), of “historical destiny” (how a current species perhaps classified on a historical destiny which prevails only for the future?).