Board Thread:Boruto Discussions/@comment-33066801-20170910125949/@comment-734582-20171007080958

Mushibrow wrote: I understand you guys knowledge about incest, but most parts in asia cousin marriage is okay Depends on how far removed they are and how often they do it. Inbreeding is more of a cumulative thing, where bad recessive traits slowly express themselves and over generations degrade the gene pool. A one-time act may not do much, sure, but it's the damage done over generations that makes incest undesirable.

It's also not so much birth defects as it is bad genes in general. Higher risks for cancer, diabetes, other genetic diseases, bad bones (e.g. bad hips), muscle problems etc.

To bring it closer to the actual topic though, the part that started this: Ice4747 wrote: If naruto is a descendent of hagaromo and Hinata is a descendant of hamura aren't naruto and hinata cousins removed maybe a hundred times or however many generations have passed. In fact if all people who have chakra are just descendants of hagaromo and haruma aren't all people with chakra related? Based upon some crude calculations i did, yes technically everyone in the world is related. That doesn't mean that those relations are equivalent. We clearly see differences in the different clans, meaning that some (especially those with KKG) probably kept their blood relation purer. This probably involved intra-clan breeding, although outside Konoha many KKG users were simply eradicated so it may be statistical bias.

Whether Naruto and Hinata is incest depends on how far back you're willing to go. I mean, the term "incest" has a pretty specific meaning, and if the trace back is a common ancestor 1000 years ago, i'd say using the term here would be pretty weak, especially since both are part of a clan in a different part of the world with little known interaction.

On the other hand, we've seen with Ashura-Indra that advanced KKG may be dormant or spit in the genepool, so the Jougan may simply be a power that was never manifested (in known times, since the Warring States Era was a big grey era) because the holders of the KKG parts never met.

This is, after all, also technically true for Wood Release, since it was never manifested after Hashirama yet his kids bear at least some of his genes. In other words, KKG aren't one-gene wonders, and different genes may combine into different KKG.