Ditto that! And, you're correct that the blood types have to do with various antigens. O- (negative) literally means that they have zero antigens in there blood...thus the universal donor status. There is no foreign antigens in the blood to react to given a transfusion situation. AB+ (positive) has both A and B antigens in there blood, along with the positive RH factor, thus they can recieve any type of blood due to all those antigens already being present in their blood. Them having those antigens means they won't have a negative reaction to a foreign antigen during transfusion cause they already have those antigens present in their blood. It is really interesting to ponder how we all aquired different types of blood if indeed we as the human race all started from the same ancestors (ie Adam and Eve). Mutations? Sure, I'll buy that, but it could have just as easily been different Alien races that started their own human line back at the beginning of time. If nothing else, it's interesting to ponder.