thank you photo and kromoh for your responses to my question. So if I gather your explinations correctly it is a little bit of both luck and having the right enviroment to feed off of.

back to the finches...the finches were in a way lucky to get the kind of beaks they did, but at the same time they were in an enviroment that allowed that mutation to be an advantage, so they stayed and propogated in it...where as the finches with other mutations went to a different enviroment that better suited the beaks they had and then propogated there. Correct?