D.K.
I have found that the best thing to tell a child is that no one truly knows how everything came to be, but in our family we believe...xyz...
Unless your belief is faith based, I believe you should never say "this is exactly how it happened" because you really don't know. Popular scientific theories are constantly changing (i.e. global cooling in the late 1800's to global warming in the 1930s, back to global cooling in the 1970's and now back to global warming - WHAT HOG WASH!!). Anyone that bases their beliefs on only science should know that these things are THEORIES and not facts and should be presented as such. Just my opinion though.
I also want to add that whatever your belief, please make it plain to your daughter that others are going to believe in different things and that's okay too. We don't all have to agree in order to be friends. Identical ideologies are not a prerequisite for friendship.