Q: Why do humans have various blood groups? What is the reason behind to it?

A:The origin and development of human blood groups is likely a part of human evolution representing the constant struggle between inherited traits and environmental challenges as early peoples adapted to changing climates, mutating germs, and uncertain food supplies. 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 much of the distinctions between the blood groups involves basic functions of our digestive and immune systems. New studies on mitochondrial DNA (mtDNA) indicate that humans evolved from a common ancestor. These studies also confirm the theory that the blood groups evolved as migratory mutations. 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 metabolised 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. The effects of ABO blood group on survival against most forms of epidemic illness is so distinct that a modern day map of the ABO blood group distribution in Europe closely parallels the locations of major epidemics, with higher densities of blood group A and lower frequencies of blood group O in areas historically known to have had long histories of repeated pandemics. On the other hand, in pre-urbanization days the survival advantage would have laid with blood group O as they are known to be more resistant to the flukes and worms that routinely parasitized these early humans, probably because they are the only blood group with antibodies against two other antigens, A and B. These changes are reflected in the local success or failure of each of the blood groups, which appear to have each had a moment of pre-eminence at a critical juncture in our history. The ascent of humans to the top of the food chain (the early advantage of blood group O), the change from hunter-gathering to a highly concentrated, urban environment and agriculturally-based diet (the ascent of blood group A), and the mingling and migration of the races from the African homeland to Europe and Asia (the opportunity for blood groups B and AB).