Speciation

Speciation is the formation of new species. A species constitutes one or more population of similar organism

Population of a species are similar because they share the same gene pool. Gene pool is the total number of different kinds of genes (or alleles) contained by all the members of a species

Population of a species may inhabit different geographical areas and so live under different environmental conditions, hence is unit of evolution. Through elemental forces of mutation and natural selection the organisms get adapted to their environment and become different from each other. So long they interbreed among them they continue to be the member of same species e.g. human races from different parts of the world viz. Europeans, Negros, Indians, Mongoloids look so different from each other but they are the same species.

Allopatric speciation : New species arising from a geographically isolated population.

Sympatric speciation : New species arising from a segment of populations of near areas due to reproductive isolation.

Phyletic speciation : Formation of species by accumulation of variations with passage of time.

Gradual speciation : New species formed by slow and gradual changes in an isolated population.

Abrupt or Rapid Speciation : Formation of new species very rapidly, Polyploidy is one such genetic process which leads to this kind of speciation.

Species Concept

Various methods have been used to define the species as the basic unit of classification and to fit it into phylogenetic scheme

Davis and Heywood defined species as the group of individuals with common morphological features and separable from other such assembly

Biological species : Mayr (1942) defined species as a reproductively isolated group individuals.

Sibling species : When two species are morphologically identical but do not normally interbreed. E.g. Drosophila pseudoobscura and D. persimiles.

Polytypic species

Morphologically and geographically separated species grouped together on the basis of interbreeding are called polytypic species

Evolutionary species

According to Simpson (1961) it is a lineage evolving separately from other and with its own evolutionary role and tendencies (= megaevolution). This method of identifying species includes morphological,

genetic, behavioural and ecological variables.

Lumpers– Combine the population to remain in single group or species

Splitters– Separate the same population into different group or species