How does speciation occur?
A species is a group of living organisms comprised of members capable of sharing a gene pool or interbreeding. This implies that members of the same species have similar characteristics and are closely related to each other. They are usually able to interbreed and produce fertile offspring. Speciation is an evolutionary process. Usually, some mutation occurs, leading to reproductive isolation, and it is this reproductive isolation that causes speciation.
Reproductive isolation can occur in three ways. The first is allopatric speciation. This occurs when members of a species split into geographically isolated groups as a result of events such as continental shift. The geographic barrier prevents members of both groups from exchanging genetic materials. Gradually, phenotypic and genotypic differences begin to appear between the two groups. Initially, the geographically separated group develops into an incipient species, but over time, the process of speciation progresses to completion with the formation of brand new species.
The second type of speciation is called parapatric speciation. This happens when interbreeding still takes place occasionally between the two groups in spite of the geographical barrier between them. Unlike allopatric speciation, parapatric speciation does not give rise to two distinct populations of different species. Instead, an environmental gradient of species is created. This type of speciation is common where distinct geographical barriers don't exist.
The third type is sympatric speciation, which can occur in the same geographical location if a group inherits more than one homologous set of chromosomes from their ancestral species. This character trait is called polyploidy. It is the rarest form of speciation.