Before World War II, researchers were puzzled by the eritroblastosis fetalis, a severe disease that affected newborn children and manifested through the decomposition of red blood cells. However, the disease affected certain families and only the first child (but not always) was born healthy.
Researches found that the cause of the disease was the incompatibility between the antigens and antibodies. The enigma of the eritroblastosis fetalis was solved through the analysis
of the blood of the rhesus macaque (hence the name of the antigen) and, subsequently, the antigen was found in humans. About 85% of the Europeans carry the Rh antigen in their red cells, while 15% are Rh negative.
As it happens in most cases, the husband is Rh positive and the mother is Rh negative. If the child inherits the negative Rh of the mother, the pregnancy will be normal. But if the child has the positive Rh of the father, the Rh conflict installs.
Blood from the embryo can leak via the placenta into the bloodstream of the mother. This blood carries the Rh antigen. The immune system of the mother, not familiarized with it, considers it a threat, and the white cells will start to synthesize the adequate antibodies for the Rh antigen. With luck, this child may escape unharmed.
But with later pregnancies, the antibodies persisting in the blood of the mother will enter into the body of the embryo, via the placenta, causing eritroblastosis fetalis. The antibodies from the mother attack the red cells of the embryo, causing their agglutination and decomposition. In severe cases, so many red cells are destroyed that the embryo dies before birth. In most often cases, the child is born alive, but dies soon. Massive or total blood transfusion can save the life of the infant.
Usually, the Rh negative mothers are hospitalized in special maternities, which have the necessary resorts for saving their children. However, the Rh incompatibility can kill not only infants, but also adults in case of blood transfusions. In this particular situation, the Rh negative persons are at risk. When they receive Rh positive blood, their antibodies will attack the new red cells, causing their agglutination and death. Oppositely, an Rh negative person donating blood to Rh positive persons poses no problem.
Almost no Rh negative people are to be found in certain areas, like Africa - that's why sometimes the Rh antigen is called the African antigen. All Amerindians have the Rh antigen and, in the case of Asians, the proportion of the antigen is much higher than 85%.
On the other hand, the Basque people from northeastern Spain represent the highest proportion of Rh negative people in the world (35%) and 60 % of the individuals carries at least one Rh negative gene. The trait is recessive, meaning that a person must have a double set of Rh negative genes to be Rh negative; just one gene of Rh positive makes the individual Rh positive. This people speaks the oldest European language, belonging to a branch widespread on the continent before the Indo-European invasion 5,000 years ago, and it seems that the pre-Indo-European Europeans were largely (or entirely) Rh negative.
As American Blacks are approximately 7% Rh negative (compared to under 1% in the African populations) and 26% carry the gene, the Rh betrays a great deal of mix with European people inside this category.
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