Inbreeding may have been a common practice among early human ancestors, fossils show.
The evidence comes from fragments of an approximately 100,000-year-old human skull unearthed at a site called Xujiayao, located in the Nihewan Basin of northern China. The skull's owner appears to have had a now-rare congenital deformity that probably arose through inbreeding, researchers report today (March 18) in the journal PLOS ONE.
You know, when royalty marries their cousins it's called keeping the bloodline "pure" but when rednecks do it, it's called inbreeding. Double standards....
Oh, and how come when your rich and crazy, your "eccentric" but if your poor your just bat $%^& crazy.....Hmmm
At times I almost dream I too have spent a life the sages' way, And tread once more familiar paths. Perchance I perished in an arrogant self-reliance Ages ago; and in that act, a prayer For one more chance went up so earnest, so Instinct with better light let in by death, That life was blotted out—not so completely But scattered wrecks enough of it remain, Dim memories, as now, when once more seems The goal in sight again. --- "The Field Where I Died", Robert Browning's Paracelsus
The incest tabu is a bit of a mystery. It takes quite a bit of inbreeding for the consequences to become apparent, and even then the connection between the problems and the inbreeding takes substantial medical knowledge to understand.
Still, we have in almost all cultures (and the few exceptions tend to be of such a nature as to prove the rule) a strong ban on in-family and relative marriages. The ban is so widespread that many think it may be an inherited human instinct, not a culturally learned behavior.
Anthropologists generally think the reason for the ban is family harmony and avoiding family jealousies, not the fear of deformed children. Cultures that enforce the ban tend to do better than those that don't, to the extent that it has become universal.
The information in the OP is interesting in this context, as it would tend to show that the incest tabu was not as pronounced in the past as it is today, seeming to me to indicate that the anthropological explanation rather than the biological explanation is more probable.
Plus, 100,000 years ago the pool of available mates was a lot smaller than it has been in recorded history... If you are living in a nomadic family-tribal group of only a dozen or so families (if that many), you are going to end up 'married' to your close relations no matter how hard you try to avoid it...