More comes to light about the function of the rhesus protein. One of its functions is to prevent the blood from becoming acidic. Another is oxygen transport. Could it have been that the first ever mutation of rh negative blood took place somewhere around sea level by the sea or ocean where more oxygen supply was granted?
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Is there any possibility of a connection between the RH protein mutation and the Black Sea, which has a history of oxygen inversion with a massive impact on all organisms in and around the Black Sea? Just an intuitive speculation…