Board Thread:Naruto Discussions/@comment-945885-20140709082448/@comment-24531362-20140718063604

In-clan breeding makes a lot of sense, actually. The act of crossing over of chromosomes makes it so that even siblings can mate and produce healthy, virile young the majority of the time. And, over time, descent with modification would make it so distant cousins would be so genetically dissimilar that mating and producing defected children would be a rarity. That process has been followed by every sexually reproducing species ever. It makes even more sense when you consider selective breeding for the purpose of preserving KKG.