This bothered me long ago, but an obvious answer came to me pretty easily: As I understand it, the genetic problem of inbreeding (such as in royal families) is that the gene pool of all the members starts out comparatively uniform. All the people are genetically similar.
Adam and Eve are a whole nother story. Between the two of them, they had a lot of both dominant and recessive genes. Let’s say that both Adam and Eve had a dom/rec pair in every location. Or say one of them had totally dom and the other was totally rec. It would have taken only a couple of generations to mix up the combinations quite randomly. And if they had lots of kids, then the deck would have been quite well shuffled by even the second and third generations.
That is probaly one of the best thoughts on Adam, Eve and the whole science thing that I’ve herd in a while Keeves. but you forget a few things, Eve was made from the rib of Adam. In effect she is the biblical form of a clone. That is of course taking all divine intervention out of the picture, some thing that’s hard to do when you are talking about something that is only based on biblical terms. If she is an Adam “clone” all of their genetic codes would be the same. Adam’s first wife Lilith (if you buy into that) could work with your theory since she was made by G-d she could have any genetic code G-d wanted, but Eve was created using a part of Adam.