Final answer:
Geographic isolation is the main driver of genetic isolation in allopatric speciation, as opposed to internal events or ecological factors, which play a significant role in sympatric speciation. Geographic barriers prevent gene flow between populations, leading to diverse selective pressures and the eventual divergence into new species.
Step-by-step explanation:
Ecological speciation, internal events, and other processes can occur within a shared habitat, such as sympatric speciation or can happen when populations are split—this is known as allopatric speciation. While ecological factors and internal events such as polyploidy and natural selection affect speciation within a shared environment, they are not the cause of genetic isolation in allopatric speciation. In allopatric speciation, the primary driver of genetic isolation is geographical separation, which can occur due to various physical barriers such as mountains, rivers, or glaciers. Geographic isolation prevents gene flow between populations, leading over time to speciation due to different selective pressures in their respective environments. Examples of prezygotic and postzygotic barriers, adaptive radiation, and the rise of new species through these mechanisms illustrate the complexity of speciation processes in nature.