From a purely scientific point of view, chemical analysis of the group O antigen reveals that from a structural perspective, it is the simplest blood group and it serves as the backbone for the synthesis of increasingly complex A, B and AB. These later blood groups evolved by adding other sugars onto the basic O sugar, much like a modern city might be built upon the foundations of an ancient one. Thus if the mutations that produced the A and B antigens are ancient, the gene for blood group O is infinitely older.