In episode 6 of B The Beginning, we learn that a group of researchers:
"Without a particular plan, they began an inbreeding program which produced malformed, insane offspring the called the Promising Ones".
It seems that the incest/inbreeding probably wouldn't be relevant, especially because the researchers didn't have a clue how to work on the material (the stuff they were researching), nor how to determine if one was more or less qualified to work with it. Why then, is it included? What purpose does the inbreeding have? Or is it just to feed into anime's obsession with incest?
I tried to word the question such that it wouldn't be one giant spoiler. To anyone who is familiar with the source material, this should make sense. To others, it's just more common tropes.