Fascinating studies in the world’s leading scholarly journals show that our genetic material contains hundreds of genes inherited from microorganisms like bacteria, yeasts and viruses. There is therefore a good part of microbes in each of us and they are essential to our existence and our health.
With all due respect to religious fundamentalists, creationists and other denigrators of scientific knowledge, there is absolutely no doubt that life is the result of a long evolution from primitive organisms that appeared on Earth about four thousand years ago. – billions of years.
According to the forces of natural selection imposed by environmental variations, some of these distant ancestors remained in a simple, single-celled form (bacteria, yeasts, protozoa), while others gradually evolved. towards more complex forms, composed of an ever-increasing number of highly specialized cells.
This common origin to all living species means that even species as evolved as human beings possess characteristics that are also found in seemingly “inferior” species.
This concept is beautifully illustrated by the results of a study carried out on baker’s yeast (Saccharomyces cerivisiae), a form of life that appeared at least a billion years before us: by systematically replacing the approximately 450 genes essential for the survival of these cells by their human equivalents, the researchers showed that in half of the cases, the human genes allowed the yeasts to function completely normally.
In other words, the survival advantages conferred by these genes were so great that they were carefully preserved for a billion years, from yeast to humans.
At least 145 genes from bacteria and viruses are present in the human genome
Recent studies suggest that the transmission of genes from lower species can also occur much faster, with the help of a direct transfer between microbes and humans.
By carefully examining the genomes of some forty microbial and animal species, scientists have indeed noticed that at least 145 genes from bacteria and viruses are present in the human genome. We do not yet know the reasons for this genetic transfer or its consequences on the functioning of our organism, but certain observations suggest that this close collaboration between human and microbial genes could in certain cases play important roles.
Genes from certain viruses are a good example. It is estimated that about 8% of our genetic material is made up of DNA from retroviruses, a consequence of the many infections that have occurred during evolution. These viruses are not dangerous: we have adapted to their presence and their DNA has gradually integrated into our genome and no longer represents any danger for the body. And sometimes it’s even the opposite, because some viruses have even become absolutely essential to our existence over time!
For example, a team of American scientists recently showed that a virus called HERVK, which entered the cells of our ancestors around 200,000 years ago, is activated during the early stages of development to produce a protein that prevents other viruses from entering the embryo, thereby protecting it from infections that could block its growth.
Man, one species among many simpler ones
It is human nature to consider ourselves the most important species on the planet because of our intelligence which has enabled it to dominate the world. The results of the studies mentioned earlier remind us, however, that it would be well advised to show a little more humility and to be less anthropocentric: human beings, despite their formidable abilities, remain a living species among so many others, whose existence was made possible by much less evolved forms of life such as microbes. These origins could not be more modest should therefore remind us that each species living on the planet is related, if only in part, to ours and that we would therefore benefit from better respecting our environment…
Kachroo AH et al. Systematic humanization of yeast genes reveals conserved functions and genetic modularity. Science; 348:921-5.
Crisp A et al. Expression of multiple horizontally acquired genes is a hallmark of both vertebrate and invertebrate genomes. Genome Biol, 16:50.
Grow EJ et al. Intrinsic retroviral reactivation in human preimplantation embryos and pluripotent cells. Nature,; 522:221-5.