ok i'll be that guy...
i am a Christian but i don't think the Bible is this 100% factual, set-in-stone, historical document. it is a story intended to explain certain issues and themes to people. God, being omnipotent and omniscient, would probably have a hard time conversing in His dialect with a normal person. we could never comprehend the vastness or importance that way, thus the story is told like a novel, not a documentary.
more to your question...
either a) God created just Adam and Eve and thus their grandkids would all be produced through incest (possible) or God created others after Adam and Eve (also possible). the point is neither. God is trying to get you to understand He started this. all of this. whether He created monkeys that evolved into humans is not the BIG ISSUE but a trivial facet we get wrapped around.
if you keep reading you will notice lots of interesting things. people living to be 900, a guy being 'beamed up' to heaven, talking bushes, and parting seas...in my opinion, if all that happened, awesome, and if not, at least the story has been conveyed in a manner in which i can grasp (story/Bible form).
people/Christians who make a major deal out of literal translation and such are just missing the boat...take it for what it is worth, a story about God creating the earth and sacrificing His Son to save us.