The Rh Negative Blog

The Rh blood system is an evolutionary oddity

From here:

An evolutionary oddity

Nobody knows why Rh-negative blood is as common as it is. It doesn’t produce any obvious advantage in people who have it but it can create a disease called hemolytic disease in the fetus and newborns. That can happen when the mother has rh-negative blood, the baby in her womb has rh-positive blood, and the mother previously had a baby with Rh-positive blood.

Because babies with hemolytic disease can die, natural selection ought to cause Rh-negative genes to become less common and eventually disappear. But that hasn’t happened and no one knows why.