An interesting article on the role of viruses in the evolution of mankind. For a single person infected with a virus, this virus, of course, is a great evil. But for humanity as a whole, everything is far from so unambiguous.
We often have to deal with various diseases that are associated with viral infections. We hear that viruses can be biological weapons, and hundreds of thousands of people die from them. Yes, the AIDS virus has caused a pandemic all over the planet, and the Ebola virus can kill entire villages in Africa. But … There are scientists who claim that viruses are one of the important factors of evolution. How could it happen that one of the enemies of mankind helped him become the head of nature? To begin with, how viruses live in human cells and what they need from us.
Viruses infect not only animals, but also plants, fungi, bacteria and even other viruses. It is believed that at some stage of evolution, these agents separated from the cellular forms and continued to evolve in parallel. What is the purpose of the virus in striking a cell? To begin with, no virus can propagate outside the host cell, it is a non-cellular life form that contains only DNA / RNA and some proteins that protect genetic information and are necessary for the first stages of cell infection. Once in the cell, the virus needs to multiply as efficiently as possible, using cell enzymes, which in most cases disrupts its work.
In addition, very often the viral particles that are formed in the cell can kill it during exit into the intercellular space. But it’s very unprofitable to kill your house. Because most viruses have their own host, such as the human herpes virus, which infects the human race for a long time. Such viruses have adapted to their hosts and do not cause them significant harm. Therefore, approximately 95% of the world's population has the human herpes virus, but this does not threaten us with extinction.
Moreover, some scientists insist that if we got rid of our “ordinary” viruses, then, perhaps, new, more aggressive pathogens would take their place. This is the first factor in the joint evolution of viruses and cell forms (including humans), which is carried out approximately according to this scheme. A new virus affects, for example, a population of people, those members of a population that cannot cope with this virus die or become ill. And those who can at least somehow fight this disease continue to live and give birth to the same persistent children, that is, they transmit their genetic information. In turn, the virus can also mutate. That is, those strains that were aggressive and killed their owners do not have the ability to reproduce, and those that are less aggressive allow their owners to live and, as a result, successfully reproduce, like those that others.
That is why those viruses that we are not masters of, for example, animal viruses, are especially dangerous for us (cases of human infection with a plant or bacterial virus are not yet known). The same HIV "migrated" to us from monkeys that are resistant to it and do not suffer from any AIDS-related diseases. Scientists suggest that by 2300, HIV will not carry mortal danger for people as well as the human herpes virus. But if we talk about evolution, then this is not only the case.
Depending on the form in which the virus encodes the genetic information and the life cycle, they can reproduce in very different ways. One of the most interesting ways is the reproduction of retroviruses. These are RNA-containing viruses that, once inside a cell, synthesize DNA from this RNA, this DNA integrates into the host genome, and already from it, together with useful proteins, the cell synthesizes viral as well. A cell doesn’t know which DNA it is and which virus it is, since this DNA is in my genome, it’s worth doing what is written on it. And if such a virus is embedded in germ cells, then it will be very easily transmitted in a vertical way, that is, from parents to the child. And the child will pick up a couple more of these viruses and pass them on to his children, and so on.
Over time, the immune system will respond to some viruses and learn how to deal with them, and the viral DNA that is deactivated in the genome, but perhaps there are some sequences in the DNA that were not in the cell before, and they can greatly facilitate its life then the “smart” cell will not deactivate them. It is believed that 5-8% of the human genome contains retroviruses. Yes, perhaps this is a “time bomb,” as some scientists say, and once these retroviruses can come to life, but maybe this is the reason that we are what we are. Nature is not stupid; it will not do anything to its own detriment. So it’s worth fighting new epidemics, but don’t be too afraid of them, because there are two ways: either development or degradation, there is no other way.