Editors: Michio Okamoto, M.D., Norio Fujiki, M.D. & Darryl R.J. Macer, Ph.D.
Director, Kyoto Pasteur Institute
To consider problems related to human genome, it seems to be worthwhile to think about evolution in which the genome was created, and to learn about how the Nature succeeded in creation of the wonder of human genome.
When the first living organism, unicellular bacteria, appeared on the primitive earth some 3.5 billion years ago, molecular oxygen did not exist in the atmosphere and the air was composed only of carbon oxide, ammonia, hydrogen, methane, hydrosulfite, nitrogen, etc. The primitive bacteria utilized these gases and sunlight as the source of energy for the survival. Meanwhile, small amount of molecular oxygen began to be produced as a waste product of their light synthesis and was released into the atmosphere. The oxygen molecule, easily changeable to superoxide radicals, was highly toxic to the anaerobic bacteria, as it is today for most of the living organisms. Fortunately, most minerals on the primitive earth was highly reduced state and adsorbed almost all of the molecular oxygen so that the oxygen concentration in the atmosphere of the earth remained very low. During these 2 billion years, bacteria elaborated efficient photosynthetic machinery and gradually developed into unicellular and multicellular plants. They produced more and more molecular oxygen. Until 0.5 billion years ago, when the early Cambrian era began, the oxygen concentration of the atmosphere, as estimated from analysis of deep sea sediments, did not exceed 1%. Reentering into the Cambrian era, however, oxygen concentration began to increase remarkably breaking the limit of 1% (the Pasteur point). That means respiration consuming the molecular oxygen can produce energy much more efficiently than anaerobic fermentation. Nineteen times more ATP can be produced from 1 Mol glucose than in fermentive process. Animals can utilize molecular oxygen to create a great amount of energy for their life.
Another important effect of oxygen accumulation in the early Cambrian era was chromosomal damage that the active oxygen caused through breakage of DNA. Extremely high rate of genomic changes were produced so that all the possible taxonomic forms of animals and plants radiated. This was a huge scale experiment in biotechnology of the nature. After selection of well-adapted forms, our ancestors of vertebrate were created. These large scale changes were possible, probably because asexual reproduction could produce offspring that did not survive zygote production.
From the drastic biotechnological experiments, set about by the Nature in the Cambrian era, we can learn some important lessons. Once after sexual reproduction was established, natural selection eliminates extreme mutants and stabilizes the genome. Even before the genome-stabilizing mechanism was introduced. adaptation and selection of the new forms on the earth produced beautiful animals and plants we now see. In the long run, the Nature does not produce unnatural forms. To introduce radically new ideas and new forms, the Nature spent a very long time, the more radical the changes are, the more time it takes; to introduce accomplishment of molecular biology to human life, we have to avoid drastic changes that take place during short period of time but spend enough time to be understood and accepted. In the long term, scientific progress in molecular biology will be accepted among humans.