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 humanitys 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 humanitys 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 humanitys 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%).{ New studies on mitochondrial DNA (mtDNA) support the theory that Homo sapiens emerged in Africa and only later infiltrated other regions.} Unlike DNA, which is inherited from both parents and changes minutely with each generation, mtDNA is passed directly from mother to child. It is contained in eggs but not in sperm. Since only random mutations alter its sequence, it is a more accurate measure of the trajectory of human evolution. Extensive mtDNA studies demonstrate that humans evolved from a common ancestor. These studies also confirm the theory that the blood groups evolved as migratory mutations. From a purely scientific point of view, chemical analysis of the group O antigen reveals that from a structural perspective, it is the simplest blood group and it serves as the backbone for the synthesis of increasingly complex A, B and AB. These later blood groups evolved by adding other sugars onto the basic O sugar, much like a modern city might be built upon the foundations of an ancient one. Thus if the mutations that produced the A and B antigens are ancient, the gene for blood group O is infinitely older. Another dimension testifying to the great antiquity of group O comes from the science of physical anthropology and suggests that a greater part of humanitys existence has been lived exclusively as group O.
Posted on: Thu, 22 Aug 2013 00:57:16 +0000
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