Our unshared history
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 to survive.
There is a vast span of human existence of which little is known. Archeological ruins from the beginnings of civilization have been unearthed, and there have been occasional discoveries of a more prehistoric nature, but not much else. The impermanency of our physical existence is responsible for this void; our flesh and body fluids rapidly decompose after death. Unless preserved by extraordinary means, even skeletal remains eventually crumble and disappear. Early peoples did not practice ceremonial burial. Left to the elements, bodies soon completely decomposed: "Dust to dust" was not a mere poetic metaphor. It was a recorded observation of our transient natures.
Only in the last century have scientists and anthropologists begun using biological markers such as the blood groups in the search for humanity's imprint on our distant past. These studies have allowed a greater understanding of the movements and groupings of early peoples as they adapted to changing climates, mutating germs, and uncertain food supplies. Recent analyses, using sophisticated genetic measures, have produced the most accurate picture to date of human evolution.
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. Evolution is usually considered in the context of millions of years, which is the time frame needed to explain the many differences between animals or other species. Yet humanity’s own life span provides ample time for the myriad number of small day-to-day refinements, representing the constant struggle between inherited traits and environmental challenges.
And, although evidence points to the fact that the individual genetic mutations that produced the ABO genes are quite ancient this is trivial importance with regard to the actual demographics of the individual ABO blood groups in ancient populations. In genetics it is not the actual age of the gene that matters, it is its frequency or drift. This is computed by geneticists using a formula called the Hardy-Weinberg equation. Hardy-Weinberg posits that if the only evolutionary force acting on the population is random mating, the gene frequencies remain unchanged constant. In essence if you start off with a small number of a particular gene in a larger gene pool (such as the gene for blood group B in the gene pool for ABO blood type) and nothing other than random mating occurred, at the end of a period of time, you would still have a small number of B genes in the ABO gene pool.
So something other than random mating is responsible for the present day differences in frequency between the ABO blood groups; why for example, are 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%)?
First, it can be said that perhaps the mutation that produced the B gene was just not as common an occurrence as the mutation that produced the A gene. Yet, if they occurred at the same time, why would this be? Also, if the mutations are of such paramount importance, why is the distribution of the B gene so geographically limited to an area of high concentration stretching as a belt of territory from the Himalayas to the Urals?
The answer lies not in the ancient nature of the mutations that produced the A and B genes, but rather in the discreet interactions that occurred between early humans and their environment that were under the influence of his ABO blood group. These included the areas and climates they chose to inhabit, each with their unique populations of microbes and foods that they chose to catch or cultivate.
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.
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).
Absolutely brilliant 🤩!!!