Re: Is there any advantage of having different types of blood?

There are many blood group antigens in man.  One such group is the 
ABO blood group,  discovered by Landsteiner (for a very good introduction 
& details on blood groups visit these websites) :
 http://
www.umds.ac.uk/tissue/bludgrp.html http://
jove.prohosting.com/~scarfex/blood/groups.html).

Variation & existence of different blood group antigens (such as A, B, AB 
and O) in the human population (polymorphism) shows that evolution is 
in operation. It is not yet clear what selective advantages people with 
different blood groups have. But there are studies that show certain 
diseases (malignancy, ulcers & even hang-overs) are associated with 
specific blood group antigens. (for details visit the website: 
 http://www.bh.rmit.edu.au/mls/subjects/abo/resources/
disease1.htm)