How does geographic isolation hinder or facilitates the evolutionary process?

I'mm working on a assignment and i need ot know what the answer to this isHow does geographic isolation hinder or facilitates the evolutionary process?
It facilitates the process since mutations are much more likely to be passed on to a greater percentage of individuals, due to the smaller gene pool, and any useful mutation is more likely to become established, thereby developing at first a sub-species, and after longer isolation, a new species.How does geographic isolation hinder or facilitates the evolutionary process?
the best example is australia - where their animal kingdom is totally different fr the rest of the world. kangaroo, platypus, dingo, the insects etc. its just fantastic. even the koala [variation] is different. where do u get a lazy friendly bear