When new species are formed from the preexisting species, it results in speciation. When a population is segmented due to a physical and geographic barrier, such as a mountain or barrier, and the species diverges into two species due to restricted gene flow, the formation of a subspecies or new species is as a result of allopatric speciation. However, sympatric speciation occurs within the same population without the physical barrier. It could result from differences in mating tendencies or due to post0xygotic and pre-zygotic hindrances.