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Blood–we all have it inside of us. In fact, blood makes up 7% of our body weight! On the surface, it seems that all blood is the same. But in a room full of people, you will find many people who have blood that is different from your own. How could you know?
Just by looking, you couldn't. But in the early 20th century, an Austrian scientist named Karl Landsteiner observed two distinct chemical molecules present in red blood cells. He labeled one molecule "A" and the other molecule "B." If a red blood cell had only A molecules on it, that blood was called "type A." If a red blood cell had only B molecules on it, that blood was called "type B." If the cell had a mixture of both molecules, that blood was called "type AB." If it had neither molecule, that blood was called "type O."
Like your eye color, your blood type is inherited. When you inherit one, both, or neither chemical molecule, your body develops a natural immunity against whatever molecules are not present. Therefore, in an emergency, if you need to be given blood, it is important that your blood type is compatible with that of the donor. Otherwise, your body's antigens will attack whatever molecule was not present previously.
Once you know your blood type, you need to know if you are positive or negative. No, this isn't about personality. While studying Rhesus monkeys, Landsteiner discovered a certain blood protein. This protein is also present in the blood of some people, but not others. The presence of the protein, or lack of it, is referred to as the Rh (for "Rhesus") factor.
If your blood contains the protein, your blood is said to be Rh positive (Rh+). If your blood does not contain the protein, your blood is said to be Rh negative (Rh–). This Rh factor is also connected to your blood type. If you are AB+, that means you have type AB blood with a positive Rh factor. People with O– blood have type O blood with a negative Rh factor.
Legend has it that blood type and personality are linked: Type A's are calm and trustworthy, type B's are creative, type AB's are thoughtful and emotional, and type O's are confident leaders. Who knows—perhaps the next time you are looking for people with the same personality as you, you'll ask about their blood type.
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