I’ve had up here with viruses lately. It’s easy these days to wonder if there’s anything good about them. That made me curious about why viruses exist in the first place and where they come from. So let’s take a few minutes to talk about them. This is not about the infamous SARS-CoV-2 virus that has been in our lives for more than two years, but about viruses as agents that exist in the larger context of life on this planet.
Although sometimes puzzling and frustrating, viruses are truly impressive, according to the researchers whose lives revolve around studying them. A small cluster of genes in an ingenious casing that can rapidly evolve to continue defeating cellular defenses, a virus is like a constantly adapting robot, designed to do only one thing: keep making copies of itself. Unlike all other forms of life in our world, a virus does not create its own energy to keep going; it is not made of cells and does not grow. It uses nothing in the environment except the cells of other living things, which become hosts for each replicating virus.
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We have probably identified only a small percentage of the viruses that exist in the world, and where they come from, nobody knows. “Several theories have been proposed as to whether the viruses arrived before or after the cells,” Alan Rothman, a viral immunologist at the University of Rhode Island, tells Popular Mechanics. Rothman has been investigating immunity and the pathogenesis of viral diseases in humans (ie, how a disease develops) for more than 30 years. It’s a chicken and egg question. While viruses have a structure that holds them together, Rothman thinks the genetic component driving their behavior likely came first. Why? “The structural part would not have made sense in the absence of cells,” he says.
People have long wondered: are viruses alive? But according to Rothman, asking whether viruses are a real life form is not a relevant question. “I think it’s more of a fun question and more of a thought exercise of sorts,” he tells her. The reason it’s not a practical question is that people are still trying to understand what life itself is, she explains. “So I would say that most people would probably be inclined to say that you can’t call viruses alive or at least alive, but they are a part of life. They teach us a lot about life.”
These infectious agents are everywhere. We are hosts to a number of viruses. Many of them are totally harmless to us. In fact, the bacteria in our body have their own viruses, called bacteriophages. “Each branch of life has an associated virus,” explains Rothman. And then there are viruses that can even infect other viruses. At least one such case has been discovered, he says.
Viruses really do pack a lot of information into their little genome. “It’s like a Swiss Army knife, especially small viruses,” says Rothman. “They have to use their protein to do everything. So they will have a protein that will have at least five different functions, and we are still discovering new functions for them. You know, it’s one of the funniest parts of virology to watch.”
For example, the dengue virus, which is transmitted by mosquitoes and causes high fever, rash, and muscle and joint pain, makes ten different proteins that do it all. (By contrast, humans have tens of thousands of proteins, each with a unique function.) Three dengue proteins create the virus particle itself, and the other seven proteins are responsible for all other viral functions, such as changing the structure of the virus. cell they infect, copying the viral RNA and shutting down all of the host cell’s ability to defend itself. So each protein must have two or three different functions. “They will put together enzyme functions that don’t have to be part of each other. It’s just an amazing machine,” says Rothman.
This elegant multifunctionality is great, but here’s a fact about viruses that’s truly impressive: Despite the harmful qualities of some viruses, like causing illness and death, we can thank these seemingly simple gene fragments for shaping life. as we know it. Viruses really drive home the point of evolution: that all species, and viruses themselves, are constantly in a state of flux, responding to other living and non-living things in their environment. Some of our evolutionary traits stem from retroviruses, which are a type of virus whose genes intertwine with our own DNA and are passed on to future generations.
“If you look at the human genome, there’s a reasonable percentage that are actually embedded retroviruses,” Rebecca Dutch of the University of Kentucky School of Medicine, where she studies human respiratory viruses like COVID-19, tells Popular Mechanics. While our bodies don’t necessarily use many of these inherited viral sequences, some genes have fundamentally changed our species over millennia.
3D rendered illustration of an anatomically correct group of bacteriophage viruses attacking a bacterium.
westend61fake images
About 160 million years ago, the small furry ancestor of all modern mammals laid eggs. A symbiotic retrovirus altered their reproductive traits over many generations, until mammals developed the ability to produce offspring within their own bodies. Previously, an animal did not have the ability to keep its own blood supply separate from a new organism maturing within it. But a viral gene, and probably genes from several different retroviruses, were instrumental in the development of the placenta, the organ the mother grows to keep her body separate from the new fetus. This gene likely originates from a retrovirus for proteins that cause fusion between the virus and the cell, says Dutch. “Instead of fusing the virus with the cell, it fuses the cells of the placenta,” she explains.
This change sparked an evolution that allowed the protomammalian body to remain separate from the fetus, even as it removed waste and provided oxygen and everything the developing fetus needs. “Essentially, in this case here, we hijacked something that had a virus, for our own benefit,” says Dutch. It is now part of our very genetic makeup, packaged in a gene that is involved in the fusion of sperm and eggs. “So there are cases like that. What comes out of viruses turns out to be a key part of us. It’s amazing,” says Dutch. So maybe we don’t have to worry about the ubiquity of viruses.
Viruses can, and do, turn our world upside down. But they also made us who we are. While viruses hold enough mysteries to keep researchers busy for lifetimes, scientists are certain of one thing: These strange companions will likely always be a part of life.