Re: Why hasn't natural selection eliminated the Rhesus negative gene?

 Mutations may be  beneficial or harmful or neutral (i.e neither harmful 
or harmless). Harmful mutations (the genes containing such mutations) are 
slowly eliminated in the course of evolution. Beneficial and the harmless 
mutations (without apparent benefit to the individual) are retained (ie 
passed on to the next generations).
 One of the blood group antigen is Rh (Rhesus). The presence or absence of 
the gene in a person determines whether he is Rh positive or negative.
 Rh negative individuals (those without the gene for Rh antigen) have no 
fatal ill effect associated with it. Hence the mutation (which led to Rh 
negativity) could be harmless. No wonder it is passed on generations after 
generations!