Evolution of Blood Types
Back in the early days of man, there were only blood type O people. This means the surface of the red blood cells had neither A nor B antigens on it. This has carried down until today, when the vast majority of people are still type O.
Around 20,000BC, a mutation occurred, and some people began to be Blood Type A. These people developed an A membrane or antigen on the surface of their blood cells. This blood type became common in central Europe as well as Scandanavia. Many feel this change occurred when farming became common in those areas.
The next change was around 10,000BC. This is when some people developed a Type B membrane on their blood cells. This change took place in Asia and Japan, and biologists are not sure what encouraged this change to take place.
It was not until around the 1500s that the A groups and B groups began to mix as travel became more and more common. This formed the AB blood type, which is most common now in northern India, even though it is still the rarest of the four main blood types. Only 5% of US residents are blood type AB.
Since the different blood types really only matter when you have a blood transfusion, it is only in the past few hundred years that having different types of blood mattered at all - and it was only in 1909 that doctors finally figured out what caused some blood transfusions to work and others to fail!
More about Blood Types
Blood Types, Inheritance and Paternity
Blood Type Distributions Around the World
Blood Types and Transfusions
Blood Types and Illnesses
Important Types of Blood
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