Beware of your blood type

I just skimmed through Human Biological Variation today. It was somewhat disappointing, the exploration of topics was often too superficial and I really didn't need a review of what mitosis, meiosis and Hardy-Weinberg Equilibrium were. They do collate some interesting data in the latter portion of the book, but the only one I'd like to pass on is about blood groups. This is one genetic trait which most of us happen to know about our own status in regards to, I'm an A, my father is a B and my mother is an A. But we are often under the impression that this is capricious, and the variation in frequency of the different alleles is a function of random genetic drift. This is not totally true. Below is a copy of table 4.6 from the book: The worldwide frequencies are O at 63%, A at 21% and B at 16%. ...