When we think of the biotic realm, we are usually thinking of things that are alive. But, is a virus a living organism?
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What I had hoped to accomplish in this diary is to show how the biotic realm of the very small, primarily viruses and bacteria, have been a driving force in the evolution of life on Earth. I think we can take that as a given. Instead, I got very interested in learning more about viruses, and I’d like to share with you some of what I’ve learned. Regardless of whether a virus is scientifically a living organism, it sure acts like one, and we’ll proceed in that sense.
Most people would agree that if you came across something out there in the woods and you (you’re a scientist now) wanted to determine if it was alive it would have to be able to do at least these five things:
- Eat (consume energy)
- Poop (excrete waste matter)
- Make babies (reproduce)
- Grow (change from baby to adult)
- Move on its own (respond to stimuli)
By these very simplified criteria it can be argued ‘till the sun comes up that a virus is not a living organism. Let’s look at it a little more in depth.
From Khan Academy, there are seven criteria. The following is highly paraphrased by me.
Living things must maintain homeostasis.
A living thing must be able to control its internal temperature and internal contents. Since viruses do not have nuclei, organelles, or cytoplasm like cells do, they can’t monitor or change their internal environment. In short, viruses fail the homeostasis test.
Living things have different levels of organization.
Structure indicates complexity, complexity implies organization. Viruses are built up from smaller, less organized structures into a larger, complexly organized final structure. From nucleic acids come the DNA and genes of a virus, and from elemental molecules comes the highly complex protein coat of a virus, called a capsid. So a virus passes this test easily.
Living things reproduce.
No argument here. Or is there? Unequivocally, viruses replicate. But, and it’s a big but, they cannot do it all on their own. They absolutely require host cells to make more of themselves. With no organelles, nuclei, or even ribosomes, viruses lack the “tools” to make copies of their genes, let alone whole copies of themselves. They must hijack the host’s cellular equipment to copy their own genes, build new capsids, and assemble it all together. They can replicate, yes, but not truly “reproduce”; certainly not in the sense that a simple one-celled organism like a bacterium can. So a virus answers this test with a qualified “maybe”.
Living things grow.
Fail. Living things grow by using energy and nutrients to get bigger and more complex. Viruses emerge after replication in their fully-formed state and neither increase in size nor complexity. Can’t be more plain than that. Viruses do not grow.
Living things use energy.
In a way, viruses do and they don’t. Energy certainly gets consumed in the building up of nucleic acids to form capsids, for example. On the other hand, almost all living organisms have more than one energy resource at their disposal. We get most of our energy from consuming a variety of foods. Viruses are solely dependent for their existence on what energy their host’s metabolism is able to supply. On their own, with no host, viruses cannot take in energy. So for this test it’s another “maybe”.
Living things respond to stimuli.
Very tricky question to answer. The consensus in the scientific world is that response to a stimulus is defined by an almost immediate reaction to some change in the environment. Whereas viruses don’t respond to touch or sound or light in the way that cellular organisms do, it cannot be definitively stated that viruses do not respond to anything. This test stands at “unknown”.
Living things adapt to their environment.
Hands down winner on this one. Boy howdy can viruses adapt to their surroundings. They just take awhile to do it. A virus can live in two different phases — lytic and lysogenic. In the former the virus actively replicates in a host cell and in the latter the viral DNA incorporates itself into the cell’s DNA and multiplies whenever whenever the cell multiplies. When the host doesn’t have enough energy or supplies to support active virus replication, the virus will switch to to the lysogenic phase. When host conditions change back to the favorable so does the virus, back to the lytic phase. This switching is what leads to viral genetic mutation and these mutations are why it’s very hard to design effective and long-term usable anti-viral drugs and vaccines. Because at least a few of the targeted virions (a virion is an individual virus) will dodge the bullet, mutate, and become resistant, they can go on to infect more cells and develop highly resistant new strains.
Let’s tally up the score. Pass: two. Fail: two. Don’t really know: three. What to say?
Luis P. Villarreal offered this in Scientific American: (I highly recommend clicking the link, when you have the time, to read the entire article.)
In an episode of the classic 1950s television comedy The Honeymooners, Brooklyn bus driver Ralph Kramden loudly explains to his wife, Alice, “You know that I know how easy you get the virus.” Half a century ago even regular folks like the Kramdens had some knowledge of viruses—as microscopic bringers of disease. Yet it is almost certain that they did not know exactly what a virus was. They were, and are, not alone.
For about 100 years, the scientific community has repeatedly changed its collective mind over what viruses are. First seen as poisons, then as life-forms, then biological chemicals, viruses today are thought of as being in a gray area between living and nonliving: they cannot replicate on their own but can do so in truly living cells and can also affect the behavior of their hosts profoundly. The categorization of viruses as nonliving during much of the modern era of biological science has had an unintended consequence: it has led most researchers to ignore viruses in the study of evolution. Finally, however, scientists are beginning to appreciate viruses as fundamental players in the history of life.
There it is: whatever else we may think about them, viruses have played no small part in the history of life and evolution. Our human immune systems have had to adapt to viruses and that’s evolution.
But the itchy question still scratches at my brain: why viruses? What unfathomable processes brought them about? Aren’t they generally bad for life? I think that most of us think that way, but it ain’t necessarily so. I’ll leave you with this:
Discover Magazine. Sometimes, Viruses Can Be Good For Your Health.
Imagine that you have a devastating heart infection that won’t respond to medication. For one 76-year-old man, that nightmare was his reality. Following surgery for an aortic aneurysm — which makes the heart’s main artery swell to almost twice its normal size — a nasty bacterial infection caused by the microbe Pseudomonas aeruginosa had taken over.
Beyond that, the bacteria in his body slowly became resistant to even massive doses of antibiotics. The septic infection became so bad that a cavity grew in the patient’s chest; drainage began to erode his aorta, making surgery highly risky. Desperate, the patient and his doctors tried an experimental treatment that would become known as “phage therapy.” In January 2016, doctors injected him with a mixture of antibiotics and hundreds of millions of viruses called OMKO1 that were found in a pond in Connecticut.
The idea was that this virus would target efflux pumps that P. aeruginosa had evolved to spit out bacteria-killing drugs. The bacteria would then evolve new resistance to the virus by deleting these pumps — but this selection would make the pathogen susceptible to antibiotics again.
It worked. Four weeks after the injection, the patient had unrelated surgery, and doctors found no trace of P. aeruginosa. A case study was published in 2018, and Paul Turner, an evolutionary biologist at Yale University who worked on the case, says he has since treated 13 patients using phage therapy. All 13 have recovered, although the results are still pending publication.
Phage therapy highlights just one of the many ways viruses can — and do — benefit humans. In the middle of the COVID-19 pandemic, people are understandably furious at the coronavirus responsible for such widespread destruction and death. It’s remarkable, and tragic, that something so tiny can gain such a tremendous foothold on our society. But not everything viruses do are inherently harmful.
The Good Ones
In many cases, we’ve been able to wrangle viruses to do our bidding. Thanks to their unique ability to worm into DNA, viruses can be used to inject genes into cells, which can reverse some genetic diseases. For example, some viruses have been able to cure hemophilia, a blood disorder that prevents clotting.
Viruses have also helped illuminate how the human mind works, using a technique called optogenetics. It involves the use of viruses that have been genetically modified with light-sensitive cell receptors lifted from green algae.
When injected into the brain, these viruses are able to modify the DNA of specific neurons, allowing them to be switched on or off by flashing those brain cells with blue light. By observing what happens when these switches are thrown, neuroscientists have developed new theories on how things like depression and addiction become ingrained in the brain.
Hope no virus has you down. Stay safe, stay masked in public.
Now It's Your Turn
What have you noted happening in your area or travels? As usual post your observations as well as their general location in the comments.
Thank you.
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