In my opinion, I think it's more of the dog as an individual and it's surroundings. Maybe if they had a shit load of people bitters in their lineage and on the same yard as them, they might be more prone to bite someone. My pup now, she's Jeep/RB/Rascal bred got her at 4 months, is very standoffish until she gets use to you. Who knows if she will bite someone or not, I don't "think" she would, but I still tell people if she wants to let you pet her she'll come up to you. Sometimes I wonder if she was mistreated the first few months before I received her, who knows. All in all I don't think it has to do much about the lines, but I'm no expert. Well said Jack, if I feed you everyday, you know me and one day you try to get at me......you're done buddy. I had a Rottweiler that was like the dog you're describing S_B, she was a nice dog but when she had her dish full, her fat ass would let you know she wasn't done eating. Not sure how to correct it, just keep working with her the best you can and hopefully the day will come that she doesn't care if you reach for it. Just my 2 cents