The reason for the importance of this antigen is that a mismatch in the D antigen can prove fatal during blood transfusion, just like it does in AB antigen mismatch.
So A ve means a blood group which has A antigen and Rh D antigen.
Some evolutionary gene modifications might prove fatal when exposed, but are nevertheless are useful while they remain dormant and hence are continued to be carried.
For instance, Sickle Cell anemia is a fatal disease where RBCs sickle up causing life threatening complications.
Tests are done during early stages of pregnancy, and if the mother is Rh -ve and the child is Rh ve, then an injection which prevents the mother’s immune system from generating antibodies against Rh D antigen is given during pregnancy.
This will ensure that the fetus remains unaffected by the fact that the mother’s blood is Rh negative and ensures a safe delivery of the child.
So what about blood groups like B ve and O-ve which we keep hearing about?The human blood group classification is based on these antigens on our Red Blood Cells (RBC), and there are around 32 Human Blood Group classifications based on the various antigen groups.ABO is a classification of human blood group based on the presence or absence of A or B antigens.Some recent studies have indicated that Rh negative people are resistant to some parasites like Toxoplasma, or to their effects on the body.So it might as well have served an advantage in this geography NOT to have the Rh D antigen, rather than have it. And one can find many such instances across human evolution.