[Ronaldus Magnus]

...which means that we must receive both our parental genes as O to have an O blood group phenotype.

The ambiguity in this statement is that we only receive one respective blood group gene from each parent. Another way to think about this is that the O blood group would have been eliminated early on if it actually required two O type parents to propagate it.

[blam]

"Another way to think about this is that the O blood group would have been eliminated early on if it actually required two O type parents to propagate it."

Oppenheimer does go on to explain why O types haven't disappeared. But, I'm not going to type any more of that book to FR, LOL.