Final answer:
Speciation events, like allopatric speciation, result from long-term isolation where geographic barriers prevent gene flow, leading to the evolution of new species from previously interbreeding populations.
Step-by-step explanation:
Long-term isolation leading to a speciation event, such as allopatric speciation, occurs when a population of organisms is geographically separated, preventing gene flow between the separated groups. Over time, the isolated populations evolve independently due to environmental pressures, mutations, and natural selection. This can result from various geographic barriers, like the formation of a river or a mountain range, or long-distance dispersal events, such as seeds floating to an island. Instances of such isolation include the diverse species of squirrels on opposite sides of the Grand Canyon, which were once a single species but diverged due to isolation. Allopatric speciation is one of the most common ways that new species arise, with geographical separation playing a critical role in dividing populations.