Why Do Blood Groups Make Humans Unique?

Nowadays, several lives are saved due to blood transfusion, but before the discovery of blood types, countless lives were lost. Blood transfusion was done by transfusing animal blood into humans which resulted in vomiting and instant death. British physician James Blundell, stressed by the death of female patients due to blood loss during childbirth, was convinced that blood transfusion would save their lives. He was the first one who insisted that humans should receive blood from another human, not a different species. Blundell injected blood in the arm of a person bleeding to death who felt better after the procedure but died two days later. The experience, nevertheless, encouraged Blundell to continue his experiment. In total, he performed 10 blood transfusions of which four patients survived.

The type of blood coursing through your veins is likely different from the blood in your friends and maybe even your family. Knowing your blood type is important for blood transfusions and other medical purposes, which raises a question: Why do blood groups make humans unique?

Human blood is categorized into four different types: A, B, AB, and O. Before the 19^th century when a patient lost too much blood, erroneous practices of animal blood transfusion cost many lives. Most scientists preferred avoiding the practice of transfusion, even from humans. Blood groups were first discovered by an Austrian Scientist named Karl Landsteiner in 1900, for which he also won the Nobel Prize.

• Blood group A is chronologically the oldest found blood type, and it existed before the homo sapiens evolved from their primate ancestors.
• Blood type B was discovered some 3.5 million years ago, due to genetic mutations that shifted one of the sugar molecules that sit on the surface of RBC (red blood corpuscles).
• Due to further mutations, the sugar gene disappeared from the RBC creating the blood type O, which had neither A nor B adaptation of the sugar.
• Later, the rare blood type AB was found which is covered with both A and B sugar molecules.

Your blood group is determined by the type of antigen present in the cell. For instance, if only an antigen of type A is present in your blood group, then it is classified as blood type A, and vice versa for B. If both A and B are present, then it is of the type AB, whereas if there is an absence of both the antigen then it is O-type blood. So, if the blood of a type A person was donated to a person with type B blood, then the receiver’s immune system would perceive the unfamiliar sugars as an intruder and attack it, resulting in the death of the receiver.  

The positive and the negative sign of your blood group indicates the presence or absence of an antigen known as the Rh factor. The Rh factor is an inherited protein found on red blood cells. Rh factor is significant in blood donations and transfusion.  A person with a +Rh factor does not make -Rh antibodies but individuals with -Rh factor does make them. Therefore, someone with a +Rh blood group can receive blood from both Rh factors but those with -Rh factor can only receive blood from -Rh. If blood containing different antigens is transferred to a person, their immune system will fail to recognize the antigen and attack it. 

You might have heard the terms ‘universal donor’ and ‘universal recipient’ before. What these refer to is an individual’s ability to accept blood from another human. If the blood types are not compatible, red blood cells will clump together, forming clots that can block blood vessels and cause death.

Since Group O- has none of the three antigens, but does have all three antibodies, their bodies react violently to a transfusion from a blood Group that might have any kind of antigen. Hence, they can only receive blood from another Group O- individual. The absence of antigens also gives them the ability to donate blood to anyone, so these individuals are called ‘Universal Donors’. Similarly, since Group AB+ people have all three antigens and none of the antibodies, so they can accept blood from any individual without risk. This makes them ‘Universal Recipients’.

Although a concrete reason for the existence of ABO genes that determine blood types is not known, even after a hundred years of discovery, scientists believe that there must be an evolutionary advantage. Interestingly, in 1952 Bombay, doctors reported people that had none of the recognizable blood types normally found in humans. This phenomenon could mean that there is no evolutionary advantage after all, but these are very rare. Claims have been made that people from group A have the worst hangovers and group O have the best teeth, for example, but these associations are probably coincidental at best.