ABO blood group system During the 1930s, connecting blood groups to personality types became popular in Japan and other areas of the world. Studies of this association have yet to confirm its existence definitively. Other popular but unsupported ideas include the use of a blood type diet, claims that group A causes severe hangovers, group O is associated with perfect teeth, and those with blood group A2 have the highest IQs. Scientific evidence in support of these concepts is nonexistent. ABO blood group system The ABO blood group system is used to denote the presence of one, both, or neither of the A and
Blood blood clotting in a transparent container. When blood is drawn in a glass container and left undisturbed for about an hour, four different layers can be seen. A dark clot forms at the bottom (the "black bile"). Above the clot is a layer of red blood cells (the "blood"). Above this is a whitish layer of white blood cells (the "phlegm"). The top layer is clear yellow serum (the "yellow bile"). The ABO blood group system was discovered in the year 1900 by Karl Landsteiner. Jan Janský is credited with the first classification of blood into the four types (A,