Blood Group Distribution Today
Overall, there such large populations of blood group O (40-45%) and A (35-40%) versus much lower rates of groups B (4-11%) and AB (0-2%). By looking at the distribution of blood groups today, we can see the threads of our evolutionary history. In the United States, O is the most prevalent blood group, A is second, followed by B, and finally AB. The breakdown in Great Britain is very similar to the U.S. percentages. In Germany there are slightly more A than O; B and AB remain almost the same as U.S. percentages. In Japan and China As, Os and Bs are fairly evenly split, and the AB percentage increases over that found in European populations.

Evolution In Digestion and Immunity
The variations, strengths and weaknesses of each blood group can be seen as part of humanity?s continual process of acclimating to different environmental challenges. Most of these challenges have involved the digestive and immune systems. It is no surprise, then, that many of the distinctions between the blood groups involve basic functions of our digestive and immune systems.

Back in ancient times, as humans migrated and were forced to adapt their diets to local conditions, the new diets provoked changes in their digestive tracts and immune systems, necessary for them to first survive and later thrive in their new habitats. Different foods metabolized in a unique manner by each ABO blood group probably resulted in that blood group achieving a certain level of susceptibility (good or bad) to the endemic bacteria, viruses and parasites of the area. This probably more than any other factor was what has influenced the modern day distribution of our blood group. It is fascinating to note that virtually all the major infectious diseases that ran so rampant throughout our pre-antibiotic history have ABO blood group preferences of one group or another.

This results from the fact that many microbes possess ABO “blood types” of their own. It is perhaps useful to understand that the ABO blood group antigens are not unique to humans, although humans are the only species with all four variants. They are relatively simple sugars which arte abundantly found in nature. A bacteria which for example possessed an antigen on its surface that mimicked the blood group A antigen would have a much easier time infecting a person who was group A, since that bacteria would more likely be considered “self” to the immune system of a blood group A person. Also, microbes may adhere to the tissues of one ABO group in preference to another, by possessing specialized adhesion molecules for that particular blood group.

The horrors of the Black Plague, which ran unchecked throughout Europe in the thirteenth and fourteenth centuries, is a perfect example. The Plague was a disease caused by bacterial infection and was almost certainly fatal to those who contracted it in the early years of its initial spread. By the fifteenth century, however, fatalities were rare, although many people continued to contract the infection. In just two generations, traits were developed in the survivors that protected them from fatal infections. Since these traits were necessary to survival, they were then passed on and retained as a form of genetic memory. The Black Plague is especially interesting from a perspective of the ABO blood groups, since Yersinia is a bacteria with a preference for individuals of specific ABO group, in this case, group O.

Excerpted from: “Blood groups and the history of peoples” in THE EAT RIGHT 4 YOUR TYPE ENCYCLOPEDIA

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