why do we have different blood types
Harvey G. Klein, chief of the department of transfusion medicine for the National Institutes of Health, explains. The types of proteins, glycoproteins and glycolipids found (or expressed) on the surface of red blood cells define blood types. In addition, blood types, or at least the genes responsible for them, are inherited. Karl Landsteiner described the original blood types--A, B and O--in 1900 and doctors now recognize 23 blood group systems with hundreds of different "types. " Many of the blood type antigens (and the antibodies that react with them) have been discovered as a result of transfusion incompatibilities. Some of these molecules have additional functions that are at least as important as conferring compatibility (of lack of compatibility) on transfusion recipients, however. The advent of sophisticated biochemistry and molecular biology has helped to characterize a number of these entities. Although it appears that the majority of the molecules are not essential for red cell function, some have specific functions on the red cell membrane such as allowing substances to enter and exit the red cell or binding certain substances to the cell surface. For some blood types, evolution and environmental selective pressures are clearly important for their persistence. For example, the Duffy blood type includes a receptor that allows certain types of malarial parasites to enter the red cell. Thus, in some malarial areas of Africa, populations with Duffy-negative blood types have a distinct survival advantage because absence of the Duffy antigen provides a measure of protection against malaria. The percentage of people lacking the Duffy antigen is much higher in these locations than in areas not endemic for malaria. We do not yet know the functions of the A and B blood group factors. (The O blood type is defined as the absence of A and B factors. ) They are most likely important, however, because they are expressed on many cells and tissues in addition to blood cells, and circulate in the plasma as well.
There are statistical differences in the frequency of certain malignancies that correlate with the ABO blood groups: Group A subjects have about a 20 percent greater risk of developing cancer of the stomach than do group O individuals, for instance, whereas the latter appear to have a greater risk of developing ulcers. The reasons are unclear. These disease susceptibilities are unlikely to confer a significant survival advantage on a population, however, because (unlike malaria) they often occur beyond a subject's reproductive years. On the other hand, there is some evidence that group O members are more susceptible than other blood type individuals to the agent that causes bubonic plague, whereas group A people are more susceptible to smallpox virus. These correlations may account for the increased frequency of the B gene in China, India and parts of Russia, which suffered epidemics of both of these diseases. Infectious organisms that carry A- and B-like antigens may have indeed played a role in the somewhat different distribution of blood types worldwide. Finally, a number of myths exist about blood types. Claims have been made that people from group A have the worst hangovers, group O the best teeth, and group A2 the highest IQs, for example. With these and other purported associations, both the scientific basis and evolutionary significance are limited at best.
I still remember when my mother told me I had O- blood. She said it meant I was a universal donor anyone could receive my blood, but I could only take O- blood in return.
I'll admit feeling prideful of this distinction as if I've been selected for a duty to help others. It's a fact I've never questioned until recently. After all, w hat's the evolutionary advantage for having such different blood types? It certainly doesn't do us any favors when receiving a transfusion of a blood not of your type could very well kill you. Why blood types are so important discovered there are three blood groups A, B, and O. It was a huge find and he won a Nobel Prize in Physiology or Medicine for it in 1930. A few years later researchers would discover the AB group. What differentiates one blood group from another are its antigens. It's a coating around the red blood cell, which helps the body identify which cells are yours. So, if an A- patient were to receive a transfusion from a B+ donor, the antibodies in the patient's system would reject the transfused blood, attacking what they perceive as a foreign invader. This attack would cause the transfused blood to clot, threatening the life of the patient. There are two main antigens that form around our red blood cells, they are known as A and B. So, if your blood type AB, then you have both the A and B antigens. Type O lacks the A and B antigens, so the antibodies of a type O patient would attack A or B blood from a transfusion. Think of antigens as a hall pass, if your blood cells have them, then they won't get any trouble from the hall monitors (antibodies). Photo Credit: / Wikipedia The + and symbols also have significance in blood transfusions, which pertain to another set of antigens known as Rhesus or Rh. This is another collection of 45 different antigens. But they're all produced as a single group, so you either have all of them (Rh positive) or none of them (Rh negative). So, when it comes to transfusions AB+ can take any blood, whereas O- can only accept O- blood.
Back when humans first roamed the Earth, we weren't concerned with blood transfusions. But why some groups of people are more likely to have one blood type over another. Based on diagrams from Type A is thought of to be the most ancient. Pre-humans began with type A blood before early humanoids began to exhibit certain mutations in the form of other blood types, which might or might not have turned into survival advantages. So about five million years ago, this mutation pops up called group O. And around that time, and subsequently, group B developed, Dr. Christine Cserti-Gazdewhich, a hematologist at the University of Toronto, told NPR. One clue to how these mutations survived can be found in their unique resistance to certain diseases. 2007 study published in the Proceedings of the National Academy of Sciences cells infected with malaria don't stick well with type-B or O blood. So, those with the O or B type lived long enough to reproduce, while the type As died out. Infectious organisms that carry A- and B-like antigens may have indeed played a role in the somewhat different distribution of blood types worldwide, Harvey G. Klein, chief of the department of transfusion medicine for the National Institutes of Health, explain. Natalie has been writing professionally for about 6 years. After graduating from Ithaca College with a degree in Feature Writing, she snagged a job at PCMag. com where she had the opportunity to review all the latest consumer gadgets. Since then she has become a writer for hire, freelancing for various websites. In her spare time, you may find her riding her motorcycle, reading YA novels, hiking, or playing video games. Follow her on Twitter: @nat_schumaker
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