Humans have different blood types. Knowing one's exact blood type is crucial when it comes to blood donations and transfusions and other medical contexts. But why exactly do people have different blood types?

Blood Types

There are four main groups of blood, namely, O, AB, A, and B. Each blood group is marked by the antigens present over the red blood cell surface.

Type A blood contains the A antigen on their blood cells, while B has the B antigen. Type AB blood contains both A and B antigens, while O does not have any.

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Why Do People Have Different Blood Types?

Dr. Caludia Cohn, who serves as the medical director of the blood bank at the University of Minnesota, explains that the data strongly suggests that the reason behind the variety of blood groups can be found in malaria. The doctor explains that if one superimposes a map regarding where the malaria parasite is and the blood type of group O, striking similarities can be observed.

The death toll of malaria is incredibly high. In 2020, 627,000 from all over the world died due to malaria. Among people who carry the malaria-causing parasite, red blood cells that are infected end up piling within small blood vessels. This blocks the blood and the carried oxygen from reaching the brain.

Interestingly, individuals with the group O blood have been observed to have remarkable protection against malaria. For one, a 2007 study saw that individuals with blood type O had a 66% lesser likelihood of getting malaria. This was in comparison to people with other types of blood.

There is substantial evidence regarding why populations that evolved in areas prone to malaria have a blood type O. However, it remains unclear why type AB, A, and B blood have high proportions in other areas.

Some scientists think that there could be disease associations across other blood types. A 2021 study discovered that individuals with blood type O have a higher likelihood of developing tuberculosis, plague, mumps, and cholera. On the other hand, individuals with other blood types have a higher likelihood of developing other conditions. For instance, individuals with AB blood are more likely to get E.coli and Salmonella infections, as well as smallpox.

However, Dr. Cohn does not think that these associations are convincing, especially as a possible explanation for the blood type variety. Such studies did not offer any causal explanations between blood types and disease prevalence, which means that there could be other factors influencing these links. The doctor notes that malaria appears to be the only one that really seems to be self-bearing.

It is also a mystery why the majority of individuals have a protein called the Rhesus (Rh) factor over their blood cell surface. This determines whether they are Rh positive. However, roughly 1% of Asians, 8% of Black people, and 15% of Caucasians do not have this protein, which makes them Rh negative. This determines the + or - in blood types.

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