Final answer:
Allopatric speciation, where species are divided by geographical barriers and evolve separately, is more common than sympatric speciation, which occurs without physical barriers. Allopatric speciation is facilitated by dispersal or vicariance, while sympatric speciation typically involves more complex mechanisms such as polyploidy.
Step-by-step explanation:
Allopatric vs. Sympatric Speciation
Speciation is the evolutionary process through which new biological species arise. Allopatric speciation is more common than sympatric speciation. Allopatric speciation occurs when a species is divided by geographical barriers such as mountains or rivers, leading to reproductive isolation and evolutionary divergence. For example, the different species of squirrel on either side of the Grand Canyon. This geographic isolation can result from dispersal, where members of a species move to a new geographical area, or vicariance, where a natural event physically divides organisms.
In contrast, sympatric speciation occurs without physical barriers, within the same geographical area. It is considered less common because reproductive isolation without physical barriers is less likely to be sustained over time. However, sympatric speciation can occur through mechanisms like polyploidy, especially in plants.