Why we have different blood types and why they matter

• Blood types have been around for at least 20 million years. 
• Scientists are still trying to figure out why there are so many, but these different blood types can have deadly downsides. 
• Watch the video above to find out what makes a certain blood type right for one person, but wrong for another. 

Not everyone on Earth has the same blood type. Researchers are still trying to figure out why there are so many, but these different blood types can have deadly downsides. 

The surface of our red blood cells have proteins, called antigens, which define our blood type. Type A blood contains Type A antigens and type B blood contains Type B antigens. There are 35 blood groups in the world, but the two most common groups are ABO group and Rh group. These groups contain the eight blood types that dominate over 90% of the world's population.

Blood types aren't unique to humans — dogs, cats, horses, and monkeys are just a few animals that have them too. 

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