Assess the importance of variations to natural selection

Variations are important to natural selection because if every species was the same and natural selection did not like them that whole species would go extinct, if there is a variety of that species it will serve because natural selection will only take out the type of that species it does not like, for example sharks! There are many types of sharks. If all sharks where put into fresh water and they where all the same type they would all die but since there is a variety the sharks that can live in fresh water live and the ones that don't die.