This sort of question would usually be a 5 mark question. Speciation is the process of forming a new species. The first stage is when a population is geographically separated so they can no longer interbreed. These two habitats will have different environments, meaning that some organisms would be better adapted to survive in each of the different environments. Over time the two populations become genetically different since only those organisms with the alleles that make them better adapted will survive (this is survival of the fittest). Eventually the gene pools in the two environments are so different that they can no longer interbreed. They are now separate species.