It depends on how often the family was inbreeding in the past. It usually takes multiple generations for problems to show up unless both partners carry a genetic defect that can be passed on. As for why it's included so often, it's because it was commonplace to marry a family member until Charles Darwin was reminded of his family while looking at his wilting inbred garden. For context, Darwin was married to his cousin, and they had 10 children. Three of them never made it to adulthood, and another three were sterile.
Incest is mostly used for first degree relatives, meaning brother and sister, father and daughter, grandfather and granddaughter.
But inbreeding over several generations is no good, that was also common knowledge in the past.
The problem is royal families often thought of themselves as special and chosen by god and nobody outside their family was good enough, so they married inside the family to preserve their special bloodline. What could go wrong, if you were chosen by god?
Yep and to piggyback off of what you said, The Hapsburg monarchy family were strong believers in keeping their blood pure so they married each other and never any outsiders. For them, it was the same as Darwin, cousins married cousins. Nieces married Uncles and nephews married aunts and so on. The Hapsburg Jaw/Chin started coming about in later generations. With each generation, the deformity of the jaw/chin got worst. King Charles II (not the current King of England of course) was the last of his generation. He had the reading level of a 4 year old and his jaw/chin hung so far out that he couldn’t even chew his food properly. He couldn’t walk straight and he drooled. He married a few times and tried to have children but it wouldn’t work. When he died so did that family.
What you described was the Spanish Habsburg line, they had a lot of enemies, so it was difficult to find proper marriage partners outside their family and intermarriage got worse and worse.
The Austrian Habsburg line, on the other hand, thrived and their princesses were sought after as marriage partners in all European monarchies, because they survived giving birth to a dozen children, while princesses of other families were too fragile for this many pregnancies.
The Austrian Habsburg family reigned in Austria until the abolishment of monarchy at the end of World War I and their Descendants are still around, just without their titles and privileges.
He was the child of a former queen.
She said the queen was her aunt and her aunt betrothed her neice to her son?? The baby would come out looking physically messed up right??? Why was that detail glossed over??