Q & A
Blood and History

By C. CLAIBORNE RAY
Published: January 16, 2007
Q. Is there an evolutionary reason for human blood types?

Victoria Roberts
A. The blood types classified as A, B, AB and O appeared and predominated in geographically separated populations over the course of human history, and it has been assumed that the differences conferred some biological advantage. A recent suggestive study links this advantage to how different kinds of infections, bacterial and viral, interact with different blood types.

The study, by researchers at University College, London, appeared in 2004 in the Proceedings of the Royal Society.

Blood types are characterized by certain complex sugars, with the types differing genetically. When the sugars end up on the surfaces of cells, they determine how the body and an invader interact.

The researchers’ statistical model found that the rates of occurrence of these blood types closely mirrored the distribution of opportunistic bacterial infections, which are best fought off by A and B blood types, and the distribution of viral infections, which are best fought off by O blood types.

The researchers said they hoped the study could point the way to a better understanding of how the changing influenza virus could be fought off by the immune system.