Here's how it works:

* Separation: A population of a species is physically separated into two or more groups. This could be due to a mountain range forming, a river changing course, or a group of individuals migrating to a new island.

* Genetic Divergence: The isolated groups evolve independently. Over time, they experience different selective pressures, mutations, and genetic drift, leading to changes in their gene pools.

* Reproductive Isolation: Eventually, the genetic differences become so significant that the isolated groups can no longer interbreed, even if they come back into contact. This is known as reproductive isolation.

Therefore, geographic isolation can lead to the formation of new species through the accumulation of genetic differences between isolated populations.