What evolutionary role might blood antigens ABO and Rh have played in species/sub-species differentiation. Presence of a different blood type in a fetus can cause a build up of antigens that can prevent future pregnancies of different blood types. This most likely is an unfortunate by-product of the type and Rh factors being evolved either through isolation, disease resistance, or diet differences. Is it all so possible it may have developed as a sub species protection of some sort. Some believe that Neanderthal and possibly other less obvious and perhaps unknown branches of the evolutionary tree may have cross bred. I was curious as to the evolutionary protection the more subtle sub-species may have developed that might enhance its genetic survival.

Is this homework?