The process that leads to the formation of new species through geographical separation is called allopatric speciation. This occurs when a population becomes divided by a physical barrier, such as a mountain range or river, leading to genetic isolation. Over time, the separated populations may evolve independently due to different selective pressures and mutations. Eventually, these genetic changes can result in reproductive isolation, preventing interbreeding even if the physical barrier is removed, thus culminating in the emergence of distinct species.