Question

How could epidemics be responsible for the variations on blood type of different people across the globe?

Answer 1

The types of proteins, glycoproteins and glycolipids found on the surface of red blood cells define blood types. Along with that, blood types or at least the genes responsible for them, are inherited. Many of the blood type antigens have been discovered as a result of transfusion incompatibilities. Some of these molecules have additional functions that are at least as important as conferring compatibility on transfusion recipients. For some blood types, evolution and environmental selective pressures are clearly important for their persistence. For example, there are some evidences that group A people have about a 20 percent greater risk of developing cancer of the stomach than do group O individuals,whereas the latter appear to have a greater risk of developing ulcers. The reasons are unclear. On the other hand, there is some evidence that group O members are more susceptible than other blood type individuals to the bubonic plague agents, whereas group A people are more susceptible to smallpox virus. These correlations may account for the increased frequency of the B gene in China, India and parts of Russia, which suffered epidemics of both of these diseases.