Why Do We Have Different Blood Types?

Why Do We Have Different Blood Types?

Knowing Your Blood Type Is Important For Blood Transfusions And Other Medical Purposes, But Why Are Some People’s Blood Type O Positive And Others B Negative?

The type of blood circulating in your arteries is probably different from the type of blood your friends and maybe even your family. Blood type knowledge is essential for blood transfusions and other medical purposes, But why do humans have different blood types?

There are four main blood groups: A, B, AB, and O. Each of these blood groups is defined by the type of antigen present on the surface of red blood cells. Blood type A has antigen A on its red blood cells, type B has antigen B, type AB has both antigens, and blood group O has neither. Dr. Claudia Cohen, Medical Director of the University of Minnesota Blood Bank, said:

The data strongly show that malaria is the main reason we have different blood types. If we put a map of the location of the malaria parasite and blood type O, we see that they are highly correlated.

According to the Centers for Disease Control and Prevention, malaria causes high mortality. Red blood cells accumulate in small blood vessels and prevent blood and oxygen from reaching the brain in people who carry the malaria parasite. Malaria will kill 627,000 people worldwide by 2020.

But people with blood type O have considerable protection against malaria. For example, a 2007 study published in the journal PNAS found that people with blood type O were 66 percent less likely to develop severe malaria than those with other blood types.

According to a 2015 study published in the journal Nature Reviews Microbiology, this is partly because the malaria parasite causes a protein called RIFIN to be expressed on infected red blood cells. This protein acts as a glue and causes uninfected red blood cells to accumulate around infected red blood cells.

But according to a study published in the journal Nature Medicine in 2015, while RIFIN binds tightly to the surface of blood type A red blood cells, it makes a weak connection to blood type O red cells. However, blood type is not the only aspect of a person’s blood type that affects the risk of malaria.

In addition to the antigens that determine the main blood groups, 15 other types of antigens can be present on the surface of red blood cells. One of them is the Duffy group.

People who lack Duffy antigen are relatively resistant to one of the two main malaria parasites. Duffy antigen-negative is common throughout Black Africa, where malaria is most common but rarely seen in other parts of the world.

There is ample evidence that populations developed in malaria-prone areas have blood type O. Still, it is unclear why can find blood types A, B, and AB  in relatively high proportions in other regions. Some scientists point to the link between diseases and different blood types.

For example, a 2021 study in the journal BioMed Research International found that people with blood type O were at higher risk for cholera, plague, tuberculosis, and mumps. According to the results of this study, people with other blood types are more likely to have other diseases. For example, people with AB blood type are more likely to get smallpox and Salmonella and Ikolai infections.

Of course, Cohen does not find these connections convincing, and in particular, he does not see them as the reason why humans have different blood types.

Studies to date have not established a causal relationship between blood type and the prevalence of this disease. Likewise, they do not prove that blood groups are protective or susceptible to infection. The cause of communication can be other factors. “Malaria is the only case that seems to support this hypothesis,” Cohen said.

It is also unclear why most people have a protein called rhesus (Rh) on the surface of their red blood cells, Rh-positive, but about 15% of Caucasians, 8% of blacks, and 1% of Asians do not have this protein, and are Rh-negative.

It is a positive and negative sign that comes after a blood type (for example, A positive or B negative).

In a 2012 study published in the journal Human Genetics, researchers looked at whether Rh-positive has the advantage of keeping such genetics in the population despite causing rhesus disease. Rhesus disease is a condition in which a pregnant woman’s antibodies attack the baby’s red blood cells.

However, found no advantage. The researchers concluded that these benefits existed in the evolutionary past and no longer existed, or humans have two types of Rh due to chance.