Actually, as long as they aren't producing highly inbred children and the relationship is fully consensual just like any other, I've never seen any reason at all for objecting to any kind of incestuous relationship.
My thoughts exactly.
As for the inbreeding. Incestuous relationships do not produce genetic mutations. Most of the genetic disorders associated with incest are recessive, meaning that a person needs two recessive genes paired for a particular trait in order to develop the disorder. In general population those disorders are not that common because there is enough dominant genes for those traits circulating around, and when a dominant gene is paired with a recessive one, the recessive one is suppressed (hence the name). Close relatives have high degree of genetic similarity, meaning that if a particular potentially harmful recessive gene is present in the family, chances are, the hypothetical lovers might both have it (paired up with the dominant gene, hence they do not have the disorder themselves). Meaning, there is a higher-than-average possibility that a child produced by the couple might inherit the recessive genes from both parents, and as a consequence, develop the disorder. But only if the recessive gene is present in the family in the first place. It will not magically appear just because the couple is breaking a taboo.
Also, the mere presence itself of the gene in the family does not automatically mean that the child will inherit it (hence why I used the italics on key words).
Example: X (dominant gene for a trait); x (recessive gene for that same trait, harmful); B (brother); S (sister); C (child); % (chances for a particular combination of genes)
B(X,x) + S(X,x) = 1) C(X,X) - 25%, healthy
= 2) C(Xx) - 50%, healthy
= 3) C(xx) - 25%, disorder
-in total: 75% chances that the child will be healthy
Do note, that both the sister and the brother must be Xx for it to be possible (they can not be xx because then they would have the disorder themselves). One of them, or even both, could be XX, even if the recessive x gene is present in the family; it depends whether or not their parents passed it onto them. If even one of them (either brother, or sister) is XX, their child can not develop the disorder.
Equally, there are chances that the disorder might appear when the lovers are not related at all, if both their families have the gene. What I want to say, it is purely genetics, incest does not produce genetic mutations, it just has a higher possibility that potentially harmful recessive genes could be paired up. If, for example, those genes are not present in the family in the first place, then there is nothing to pair up, and no disorder whatsoever. And since we live in an age when genetic testing is available, it is not impossible for such couples to see if there are any dangers hidden in their genetic makeup in the first place.
last edited at Oct 3, 2015 3:59AM