Linda, I don't think you quite understand the point Russ is making concerning genetic defects relative to close related bloodlines. Certain bloodlines carry predispositions to certain birth defects, hemophilia for example.

When children are born of incest (that is not the case in my family, just close bloodlines i guess, not even cousins of any degree, just a perchance match on that) they usually look weird, they are often identifiable just by appearance. they are also often riddled with diseaes of various sorts because of (often several) matching genetically erred genes from both parents.

It has very little at all to do with overall mutations in the general population as a whole as you suggest. Incest is another matter altogether, which does not enable a route for the child to escape a genetic defect if one or more are present.