I feel exactly the same way. Love is beyond constancy, it's absolute. I didn't need salvia to come to that conclusion either. But unfortunately, this definition leads to much misunderstanding.
Larr_E, what happens when your neice and nephew grow up and become adults? You cannot guarrantee that the connection you feel now will always be. People change as you pointed out, and by automatically elevating those of "the same blood" you can only damage relationships as it creates labels and boundaries between you and them. Rather than seeing Neice and Nephew ( or brother/sister, wife/husband, mum/dad, etc etc), why not just see Bob, Jill, Bill, Jen, etc (whatever their specific names are)? Labels also create obligations which hides or creates fraudulent sincerity.