Why do we have different blood types?

 There are four main blood types (A, B, AB, and O) and each blood type has a different antigens (proteins) on the surface of the red blood cells. The different antigens help the body to recognize which cells are its own and which cells are foreign.

The most common reason for having different blood types is due to evolution. Over time, different groups of people developed different blood types in order to better adapt to their environment and to protect against certain diseases. Today, blood type is still used to match donors with recipients for transfusions and organ transplants. It is also used to help determine a persons risk for certain diseases and to help doctors tailor treatments to individual patients. Different blood types are also thought to have different effects on personality and behavior. For example, people with type A blood are often thought to be more calm and collected, while people with type B blood are often thought to be more creative and spontaneous. However, there is no scientific evidence to support these claims.