Where do viruses come from and are they living things?

Viruses are extremely simple and small entities, they basically have only a little bit of genetic information, which is DNA or RNA, contained in a protein coat. However, viruses are extremely successful, they appear everywhere and have an important place in the picture of life on earth. Here is the basic information we already know about the origin of viruses, how we study their origin and the question of whether they are living organisms or not. Hope this article will bring you interesting information.

Viruses don't leave fossils on rocks, they leave traces on their host's DNA, that's how we found evidence of them in the past.

To understand where viruses come from, we must first study their origins, as paleontology studies organisms in the past. The problem here is that the virus is too small, too fragile to leave fossils on sedimentary rocks. Fortunately (or creepy, depending on how you think) however, viruses sometimes leave imprints on the DNA of their hosts, which of course includes humans. And it is these traces that are the key for scientists to trace the virus in the past.

The study of archaea is a nascent field in microbiology, as it builds on a recently emerged discipline – genetics. In archaea, scientists mainly study fragments of viruses that are imprinted on their host's DNA.

These trace fragments are a by-product when a virus infects a cell, gains access to its DNA-replicating machinery, and then reprograms that machinery to produce new viruses and continue the infection. Sometimes viral gene fragments can be added to the host's DNA, so as long as it doesn't cause mutations that harm the host cell, it can stay there forever. And if this happens in a cell that forms sperm or an egg, then the viral genome can actually be passed on to the next generations of the host.

The reason ancient virologists often study them indirectly through fragments of the host's genes instead of 'dissecting' them directly is because they are so simple and reproduce extremely quickly, so they always mutate and change. change at breakneck speed. Just a few hundred years is enough for a virus strain to change to the point where the original genome is not much left. However, the traces they leave in the host's DNA are different, they change as slowly as the host's evolution rate, because the host reproduces more slowly and the mutation rate is not as high. Although these traces are not perfect, it is still possible to study, and it will certainly store information longer than a virus floating somewhere.

Tracing the same virus traces on the DNA of host species with the same ancestor, scientists have evidence dating back hundreds of millions of years

Scientists can figure out the age of viral traces in the genomes of animals by comparing them with each other. If two animals have the same trace, it has appeared since the two species share a common ancestor, and the virus that left that trace is at least as old as the ancestor itself.

The first example we can mention is the circovirus. This is a group of viruses that cause gastroenteritis in dogs. Scientists used to think that they appeared quite late, about 500 years ago. But the traces they leave on the dog's genome have also been found in cats and raccoons. So they must have appeared at least before these species split apart, that is, about 68 million years ago, around the end of the Cretaceous period.

The oldest evidence of a virus to date was found in a 2011 study. Researchers looked at the history of bracoviruses in wasps. And they found evidence that the time when this group of viruses appeared could be as old as the origin of the insects themselves. That was in the Carboniferous period, about 310 million years ago.

Another study in 2009. A gene found in mammals, called CGIN1, dates back to the earliest days of mammals, 125 to 180 million years ago. And this gene is thought to be of viral origin, because its components resemble an RNA of a virus, a retrovirus.

It is possible that this virus infected the egg or sperm cells of our mammal ancestors hundreds of millions of years ago. And now humans as well as countless other mammals also inherit it. In fact, an estimated 8% of the human genome is composed of sequences of viral origin.

Ancient virology has found evidence of virus evolution hundreds of millions of years ago. However, ancient virus researchers believe they were formed very, very long ago, billions of years ago - when life began to form.

Viruses can form themselves before cells, degenerate from a certain type of cell, or detach from the DNA of a living organism.

There are many different theories about the origin of the virus, and they are still widely believed by scientists to be hotly debated.

Virus-First Model (viruses form themselves before the first cells)

This hypothesis suggests that because viruses are so much simpler than cells, they must have appeared first, before the oldest cells. They persist for a while until life emerges and the cells begin to have the ability to self-replicate. Viruses then evolved to parasitize more complex life forms.

Escape Hypothesis (virus isolated from the DNA of a living organism)

This theory holds that viruses develop from cells, within their DNA. Our genome contains parts that are capable of copying and pasting themselves elsewhere. So some experts think that if such a part were able to make a protein coat, it could easily escape the cell and become a virus.

Regressive Model (virus degenerates from a living organism)

This theory was born when scientists discovered a giant virus, mimivirus. The name itself stands for 'mimicing microbe', ie 'mimicking bacteria'. This thing is huge by the standards of a virus, about 750nm, even bigger than some bacteria. Fortunately, they only parasitize amoebas.

Along with its enormous size, mimiviruses also have more genes, including some that are capable of protein synthesis – a feat that the virus should not be able to do. While the mimivirus still relies on the host to reproduce, what are all those genes used for? Some scientists think these genes are leftovers from a time when miuiviruses were larger, more complex, and more like a cell.

This theory suggests that there was a time when viruses lived freely, then developed a symbiotic relationship with other organisms. Gradually, that relationship goes from symbiotic to parasitic, and the more dependent on the host the virus becomes, the more complex it becomes.

Several recent studies have cast doubt on this hypothesis. Some scientists think that the mimivirus simply acquired those genes when it acquired them from the host over time.

The virus is not really a living organism, scientists see it as something that is neither alive nor dead

Determining whether a virus is a living organism or not is not a simple matter. Many scientists suggest placing the virus in the 'semibiotic gray zone', between the white of life and the black of inorganic matter. They're not alive, but they're not dead either. Others are arguing about finding a place for the virus on the tree of life, but the question is 'if there is, where would it make sense to put it?'.

To answer the question of whether a virus is a living organism or not, we need to agree on the definition of life. Scientists generally agree that life can reproduce on its own, generate energy for itself, maintain the stability of the environment inside cells, and can evolve.

The virus can reproduce, but it cannot do it on its own. Viruses can also mutate and evolve, but they have no way to generate energy. In addition, they also cannot control their internal environment. The reason they are in the 'semi-infant gray zone' is because they meet some conditions of life while others do not.

Some scientists have suggested that while not being a branch in the tree of life, viruses could be seen as entwined vines. This image can be seen as romantic or creepy depending on how you think, but anyway viruses are now ubiquitous and have a place in life on earth.

Above is an article about how we humans study ancient viruses, theories about their origin as well as their place in the tree of life. Thank you for watching and wish you all stay safe from all viruses.