Interesting article about the role of viruses in the evolution of mankind. For an individual person infected with a virus, this virus is of course a great evil. But for humanity as a whole, things are far from clear-cut.
We often have to deal with various illnesses that are associated with viral infections. We hear about how viruses can be biological weapons, and hundreds of thousands of people are dying from them. Yes, the AIDS virus has caused a pandemic across the planet, and the Ebola virus can kill entire villages in Africa. But… There are scientists who argue that viruses are an important factor in evolution. How could it be that one of humanity’s enemies helped put it in charge of nature? Let’s start with how viruses live in human cells and what they need from us.
Viruses affect not only animals, but also plants, fungi, bacteria and even other viruses. It is assumed that at some point in evolution these agents separated from their cellular forms and continued to evolve in parallel. What purpose does a virus serve in infecting a cell? To begin with, no virus can reproduce outside the host cell, it is a non-cellular life form which only has DNA/RNA and some proteins which protect the genetic information and are necessary for the first stages of cell infection. Once in the cell, the virus needs to reproduce as efficiently as possible using cellular enzymes, which in most cases is what disrupts the cell.
In addition, very often viral particles which have formed in the cell can kill it during its exit into intercellular space. But it is very unprofitable to kill your home. That’s why most viruses have their own host, like the human herpes virus, which affects the human race for a long time. Such viruses have adapted to their hosts and do not do them much harm. Therefore, approximately 95% of the world’s population has human herpes virus, but we are not in danger of extinction from this.
Moreover, some scientists say that if we got rid of our “normal” viruses, perhaps new, more aggressive pathogens would take their place. Here is the first factor in the co-evolution of viruses and cellular forms (including humans), which follows roughly this pattern. For example, a new virus affects a population of people; those members of the population who cannot cope with the virus die or fall ill. And those who can at least somehow fight the disease continue to live and give birth to the same resistant children, that is, they pass on their genetic information. In turn, the virus can also mutate. That is, those strains which were aggressive and killed their hosts have no possibility to reproduce, and those which are less aggressive allow their hosts to live and in the end successfully reproduce, both of them.
This is why viruses of which we are not hosts are especially dangerous for us, such as animal viruses (there are still no known cases of a plant or bacterial virus infecting humans). The same HIV “migrated” to us from monkeys, who are resistant to it and do not suffer from any diseases associated with AIDS. Scientists suggest that by the year 2300 HIV will not be as deadly for humans as the human herpes virus. But if we talk about evolution, it’s not just about that.
Depending on how the virus has its genetic information encoded and its 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 which, once in the cell, synthesize DNA from this RNA, this DNA is inserted into the host’s genome, and from this DNA, along with useful proteins, the cell synthesizes viral proteins. The cell does not know which DNA is its own and which is that of the virus; since this DNA is in my genome, it is worth doing what is written on it. And if such a virus is embedded in germ cells, it will be very easily transmitted vertically, that is, from parent to child. And the child will catch a couple more of these viruses and pass them on to their children and so on.
Over time, the immune system will react to some viruses and learn to fight them, and the viral DNA in the genome will deactivate them, but perhaps that DNA has some sequences that were not present in the cell before, and they can make its life a lot easier, then the “smart” cell will not deactivate them. It is assumed that 5-8% of the human genome contains retroviruses. Yes, it might be a “time bomb”, as some scientists claim, and one day these retroviruses might “come to life”, but maybe that is the reason why we are the way we are. Nature is not stupid, it won’t do anything to its own detriment. So it is 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.