What is geographical isolation? Give examples.

Geographical isolation is when populations of a species are separated by physical barriers like mountains, rivers, or oceans, preventing them from interbreeding. This separation can lead to the development of new species over time because isolated populations evolve independently. 

Examples include the Galapagos finches separated by islands, or the Himalayan mountains separating animal species on either side. Another example is the Kaibab squirrel on the North Rim of the Grand Canyon and the Abert's squirrel on the South Rim; they are the same species but geographically isolated by the canyon.

Geographical isolation is a key mechanism in evolution because it restricts gene flow and allows species to adapt differently to their environments.