In 1940, biologists Karl Landsteiner and A. M. Wiener discovered an antigen from the red blood cells of a rhesus monkey (Macaca mulatta). It is called Rh factor or Rhesus factor or antigen factor. Later they discovered the Rhesus factor from human red blood cells. If Rh factor is present in human red blood cells then it is called Rh positive or Rh+ve and if it is absent it is called Rh negative or Rh-ve.
15% of Americans, Canadians, Europeans and Caucasians are Rh-positive. 18-30% of the Berbers and Bedouins of Africa and 25-30% of the Basques of the Pyrenees carry the Rh trait. A very low Rh trait is observed in Bengalis.