Scientists sometimes study Rhesus monkeys to learn more about the human anatomy. Why? Because there are certain similarities between the two species.
A specific blood protein was discovered in Rhesus monkeys that is also present in the blood of some people. The presence of the protein, or lack of it, is referred to as the Rh 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 connected to your blood type. For example, your blood may be AB+ which means that you have type AB blood with a positive Rh factor. Or, you might have O- blood which means that you have type O blood with a negative Rh factor.