Joined: May 2007
There's also the whole "dual creation" problem. Genesis 1 and Genesis 2 describe creation differently, so some creationists consider them to be separate events. Genesis one describes the creation of the Earth and its creatures; Genesis 2 describes the creation of the Garden of Eden and its inhabitants. Consequently, there are people outside the Garden for Cain to hook up with.
It takes a lot of hand-waving, but resolving conflicts in the scriptures is nothing new to Creationists.