Speciation can happen when a population is isolated geographically. It seems that this is the most popular, and probably the only, mechanism leading to creation of new animal species (so called allopatric speciation).

Speciation can also occur in a population sharing the same area with other populations, but being isolated in some other way (reproductively, for example). This type of speciation, called symatic seems quite common among plants.

More than half of angiosperms plants is polyploidal (polyploids have more than two sets of chromosomes), and most of them are alloploidal (alloploids have chromosomes coming from different species). Alloploidy plays an important role in evolution of angiosperms plants. The mechanism of such speciation acts exceptionally fast. Crossing of two diploidal species (2n, 2k) produces a hybrid with n+k chromosomes. Such hybrids are usually not fertile, as their chromosomes are not homologous which diturbs the course of meiosis. However, creation of fertile individuals having chromosomes belonging to two species is possible. Here is an example how: Because of mutation, the chromosomes may not separate during meiosis thus becoming a part of a single gamete. Union of two such gametes can create a fertile generation of individuals having 2n+2k chromosomes.