These relationships deal with the contact of the new species with that of its ancestral species. Allopatric Speciation . This type of speciation is produced when a physical barrier separated a species into two separate areas and does not allow any further contact. Mountain building, glacial movement, river boundary movement, etc. are examples of geographical situations that can divide up a single species into two distance areas. When the species is split, microevolution will cause changes in the species to make them different in phenotype.
Small populations have a much better chance to develop into a new species than larger populations.
These small populations usually occur on the edges of a larger population. These fringe populations are good candidates for speciation. Their gene pool differs from the parent population, genetic drift will continue to cause chance changes in the gene pool of small populations until a larger population is formed. Different selection pressures are at work on there peripheral populations. Adaptive radiation is the evolution of many diversely adapted species from a common ancestor.