What Are Blood Types?
It might seem like blood is blood — it all looks pretty much the same to the naked eye. But although all blood contains the same basic components (red cells, white cells, platelets, and plasma), not everyone has the same types of markers on the surface of their red blood cells.
This short video explains why, when it comes right down to it, there are really only eight kinds of people in the world.
SEE ALSO: What color is your blood?