Geographical isolation of a species will lead to the formation of a new species if the species reproduces sexually because isolation will stop the gene flow between the isolated populations since they will not be able to reproduce. As a result, the members of isolated populations will interbreed, leading to the formation of new species.

On the other hand if species that reproduce asexually are geographically isolated, there will be no formation of a new species because such species do not need fusion of gametes to reproduce, they reproduce on their own. Hence there will be no formation of a new species.