Describe how biogeographical studies, esp. of islands and continents, explain species similarities and differences

Biogeographical studies use information for various fields, such as evolutionary biology, geography, geology, and climate science to determine how organisms evolved through time and how the moving of tectonic plates resulting in forming continents, mountain ranges and islands has affected their distribution.
Studies in this field explain how organisms that now live on different continents are very closely related and how the flora and fauna of islands are connected to one of the closest continents etc. 

The answer is a because - is an direction