lol... s_lone, I didn't answer, because your opening line very clearly states who the question is posed to. But, since no one else seems to be respecting your OP, I'll jump right in with my two cents too, even though Catholicism doesn't take the creation story literally.
As Dexter pointed out, there were apparently women around (or the Bible glossed largely over the fact that Adam and Eve gave birth to daughters as well). But, even if you assume that the only people breeding were all related... so what?
Speaking from an evolutionary point of view, we can't really be sure that there was any less incest going on in the tribes that spawned humanity. One show I heard claims that all of humanity shares a genetic marker that links us back to one common female ancestor. Our lineage is no 'cleaner' of incest from an evolutionary point of view than a Biblical one as far as I have seen proven. And speaking from the point of view of the Bible, it makes it pretty clear that they branched out as far as they could, rather than living a life of constant incest.