Why do we have blood types?
Blood types exist because of different molecules, called antigens, on the surface of red blood cells. Scientists think these variations may have helped people resist certain diseases.
The ABO system sorts blood into A, B, AB and O, depending on which antigens are present. The Rh system adds positive or negative, based on whether the RhD protein is present. These differences are inherited from parents. Austrian scientist Karl Landsteiner discovered the ABO groups in 1901 and later won a Nobel Prize.
Blood types matter for transfusions. If someone receives blood with antigens their immune system does not recognize, their body may attack the donated cells, causing a dangerous reaction. That is why blood is carefully matched before transfusions and during pregnancy.
An evolutionary mystery
Researchers are not sure why blood types evolved. Some studies suggest that certain types offer some protection against particular infections. For example, type O may give some protection against severe malaria, while some types are linked with higher risks of other illnesses. Blood types are found in other primates too.
Did You Know?
There are more than 40 recognized blood group systems, but ABO and Rh are the most important for everyday medical care.
This answer is general information, not medical advice. For a personal health question, talk to a doctor.