Questioning the Function of Human Blood Types
We have all heard of the A, B, AB and O blood types, and some of us spend our working day with these and many other types. These blood types are ancient. Humans and all apes share this trait, inheriting these blood types from a common ancestor at least 20 million years, posits a study recently published online on the website of the Proceedings of the National Academy of Sciences.
But why humans and apes have these blood types is still a scientific mystery. After Karl Landsteiner determined the pattern of the ABO blood group, he realized blood types are inherited. Later, researchers learned ABO blood types are governed by a single gene that comes in three varieties: A, B and O. (People who are type AB inherit an A gene from one parent and a B gene from the other.)
Scientists still have no idea of the utility or function of these blood antigen. Obviously, people who are type O-the most common blood type-get along fine without them. There are some interesting associations between blood types and disease. In some infectious diseases, bacteria may closely resemble certain blood antigens, making it difficult for antibodies to detect the difference between foreign invaders and the body's own blood. People who are type A, for instance, seem more susceptible to smallpox, while people who are type B appear more affected by some E. coli infections. It has also been shown that serum cholesterol levels are related to blood type.
Over the last hundred years, scientists have also discovered that the ABO blood group is just one of more than 20 human blood groups. The while we don't know the biological function of these antigens, we certainly know that they function to remind us we still have lots to learn.