What is the advantage of blood types ?
Why have humans developed different blood types and is there an evolutionary advantage?
Surely, if blood types are due to random mutations, one will be a better performer in general terms than the others?
There are four blood types: A, B, AB and O. These designations refer to the types of sugars (A, B and O) found on the surface of red blood cells. Everyone on the planet has an O sugar, and those who have no other type are known as blood group O. The other group names arise from the fact that some people have A, B or both A and B sugars attached to the O sugar.
Cells use things such as proteins and sugars on their surface for many purposes. One is to enable the immune system to tell “self” from “non-self” and distinguish “you” from every “foreign” body that may invade. Our cells have lots of different types of surface markers that tell the immune cells not only that they are self but also what type of cells they are. Red blood cells have the A, B and O markers and can also be rhesus positive or negative, depending on whether a separate marker is present or absent.
Certain blood types tend towards susceptibility to particular pathogens, but it does not follow that any type is superior to all others. Microbes vary and populations with just one blood type could be disastrously vulnerable to particular epidemics.
Additionally, types resistant to diseases from one region may be at risk elsewhere. The distribution of blood groups reflects this. For example, antigens known as Duffy antigens are relatively rare in African populations; they seem to be associated with susceptibility to malaria. Also A-type blood seems to go with susceptibility to the debilitating waterborne disease bilharzia, a disease caused by parasitic worms, and this is consistent with the distribution of type A in Africa. Such distributions are a more common selective outcome in evolution than a quick takeover by just one allele.