Alia said:
On your second point, Carrie, I agree. Very valid point. Although, child born too close in relations more often the not came out metal challenged or deformed... or even died young.
Well no, Alia, that's not quite true. More often than not the children were fine. You just hear about all the cases where they weren't. Most royal families had tons of healthy children. (Although it does seem like a lot of those families ran to girls.)
The most famous instance would be the case of hemophilia being passed down in the royal families of Europe during the 19th and early 20th centuries. It's a disorder that in the fast majority of cases strikes males rather than females. So the female children were quite healthy, or at worst only had a very mild form and it wasn't as though most of the males were afflicted either. But females do serve as carriers for the disease, so they could pass it on to their sons and grandsons without being sick themselves.
Also, in the United States as an example, marriages between cousins and general inbreeding tend to take place most often in rural areas where poverty is high. Therefore poor nutrition and all sorts of factors would contribute to sickly babies and high infant mortality. People outside the region would attribute it to those dang hillbillies marrying their first cousins, because, for one thing, that's easy and more comfortable than thinking we ought to do something about the poor living conditions in those places. In reality, poor diet and poor medical care produce more at-risk children than just about anything. The high degree of inbreeding would contribute to hereditary diseases being passed on, too, of course.
But ... no hereditary diseases in the family means nothing to worry about genetically speaking if people who are closely related by blood have children together. It's only when there is something there that the risk factors go right up. Even then, it would far more likely be something quite different from mental deficiency or deformity. And the incidence of desirable characteristics could go up, too.
That's why basing the argument for or against incestuous relationships on the idea of healthy or unhealty offspring is a poor one. The real problems with incest -- quite aside from the moral and religious issues -- are psychological, and they can be quite serious.
