Rationale
With all the vast amount of ways that viruses have evolved to infect our cells, it's no wonder that viruses have been highly successful in surviving and reproducing within humans. However, it is also amazing how successful we humans have been in fighting off these viruses. This evolutionary dance of mutual co-evolution that has been taking place between humans and viruses has been happening since our species first evolved on this planet. There are many reasons as to why this back and forth between humans and viruses has taken place. Much of it has been attributed to our "rendering of the fabric of our environment, changing our behavior, and ironically, by our inventiveness in increasing the length of quality of lives." (Karlen 1995). Essentially, what some believe, is that by constantly changing and adapting to survive, we humans have created the conditions that we live in today. To use colloquial terms, we've made our bed and now we must sleep in it. The shared evolution of humans and microbes has accelerated to a frenzied pace, because of changes we made in our environment and lifestyle.
Our changes to our environment pretty much come from two hardwired imperatives that, at the end of the day, every living thing possesses: the desire to survive and reproduce(Dr. Sharon Moalem 2007). Our need to survive and reproduce has led us to constantly experience evolution, which is simply defined as the change in genetic makeup of a population through time. Sometimes when we think of evolution we think of the process of genetically changing from primate ancestors to modern man. However, evolution and adaptation can often take place on a much smaller scale than species formation, and in fact with most cases it does. Currently, scientists refer to this phenomenon as an "Arms Race" between species or the "Red Queen Hypothesis". Ultimately, they describe this phenomenon in this way to illuminate the parallels with the Red Queen, a character in Lewis Carroll's Alice's Adventures in Wonderland. The Red Queen tells Alice, "…It takes all the running you can do, to stay in one place.", and this ongoing relationship is typical of host-pathogen interactions such as between humans and viruses. The more evolutionary advantage we gain against viruses, the more they seem to evolve better counter attacks, so that no matter how much progress we make we seem to end in the same place we started.
The truth is that we have been evolving in tandem with all of these microscopic organisms- sometimes to our benefit and other times to our detriment. The way our bodies work today is directly related to our interaction with infectious agents over millions of years. Some theories even pose that sexual attraction has a connection to disease. For example, it is believed that the smell of someone you find sexually attractive is often a sign that you have a dissimilar immune system, which will give your children wider inherited immunity then either of their parents(Dr. Sharon Moalem 2007).
Mechanisms of Evolution
One of the most prominent biologists of our time said that, "No organisms are evolving faster with more consequences than are the parasites among us" (Ewald 1994).This biologist is Paul Ewald and he continues to give talks and conduct research on the evolution of infectious disease. Ewald's statement highlights an important point about the nature of microbes. Their evolution, and in particular the evolution of viruses, is something that we should all be mindful of since much research suggests their evolution is directly tied to our own. We are also discovering it's not just humans and viruses that are tied together by evolution, in fact, "To be crystal clear: everything out there is influencing the evolution of everything else"(Dr. Sharon Moalem 2007)
Ironically, in the midst of this merciless war between viruses and humans, we have been brought closer together as opposed to driven further apart. There is growing research that supports this idea of symbiosis. This is the idea that two organisms can have a long-term relationship with each other. Recent research has posed that the close relationship between humans and viruses has given both of us benefits for survival. The reason this concept is taking such hold on the scientific community is because the evidence of these types of relationships are being discovered more and more frequently.
One leading science writer, Carl Zimmer, explores the idea of introgression, essentially the movement of a gene from one species into the gene pool of another, and speaks about one example in particular that is more familiar to us. It is now accepted that mitochondria organelles (aka power plants) in our cells, are derived from bacteria that once existed millions of years ago and became symbiotic with the cells of eukaryotes such as humans. Recent research from French biologist, Jonathan Filee and Patrick Forterre, has suggested that the mitochondria also possess genes from viruses. Mr. Zimmer explains that, "The invading virus's DNA simply became a harmless part of its host's genome. In many cases, the genes of cryptic viruses have suffered major damage from later mutations and many of their genes have been cut out of their host genomes altogether "(Zimmer 2005). This might help us explain why it might have taken so long to discover this type of DNA in the mitochondria.
The research is fascinating and tantalizing to say the least. "It suggests that we are chimeras built from the DNA of eukaryotes, bacteria, and viruses, all mixed together through a natural version of genetic engineering"(Zimmer 2005). If this is true, then we must reevaluate how we assess our past and who we are as individuals. The old adage states, "you have to know from whence you came, to know where you are going." Accordingly we must now look through a different lens to understand where we came from and where we are headed. Zimmer goes on to say, "Forterre even argues that these sorts of results are going to turn out to be the tip of the iceberg. Like many scientists, he believes that before life was based on DNA, the Earth was inhabited by RNA-based life. He argues that DNA was an invention of viruses of these RNA-based organisms, which the RNA-based organisms then seized for their own use"(Zimmer 2005).
So it should be clear why I compare the human-virus relationship to war. The constant rate of adaptation we have discovered lets us know that this war is far from over. Especially, when we take into consideration the rate at which mutations are taking place. Some may view our situation as dire or doomed to fail; however maybe we are just using the wrong perspective. If we can somehow learn from viruses about how to be more efficient at surviving, then maybe we can extend our lifetimes and learn to live in harmony with the viruses that vastly outnumber us in this world. If you can't beat them, join them, is what they say and maybe that's the case for some of our more virulent viruses. Unfortunately, we know that in many cases the only option for our well being, is eradication of a virus that causes serious disease in humans, such as smallpox. I believe Arno Karlen said it best with this statement, "They like us, are trying to adapt and survive. Some must be conquered, some require a wise truce"(Karlen 1995). Identifying which virus deserves which treatment is the key, and maybe the most difficult task to achieve, but I guess these are the trials and tribulations of war.
When engaged in any warlike scenario, the first thing to understand is who you are fighting. Additionally, we should begin to understand that species, in general, are designed and crafted through natural selection to fit perfectly into their space in nature. Therefore, when you look at each organism that inhabits their niche naturally, you begin to understand what characteristics they possess that allows for them to survive there. Accordingly, the fit of an organism to its environment is the result of its history, the action of natural selection gradually modifying populations over the course of time(Marks 1995). The mutations that an organism possesses are what allow them to survive, so one would think that the reason mutations happen is so that we can adapt and survive in our environments. However, that is not the case. In fact, mutations have no purpose at all. Mutations happen often, very often to be precise; it is just that most of them we don't see or are just not recognized. This is because most mutations are neutral, having little to do with adaptation(Marks 1995). It just so happens that every once in a while a mutation will present an organism with an increased fitness for the environment, stimulating the process of evolution, and the ability for these mutants to take over the population.
If most mutations are neutral, why is that biologist's claim that all organisms we see today are some form of mutant, including ourselves? One reason is that most organisms of the same species share the same mutations, so they are harder to recognize. Another idea that helps put this in perspective is the massive amount of people that live on this planet. When that many organisms exist it opens the door for that many more mutations to occur. We are mutating often because we are reproducing rapidly, and any child could have a mutation differing from its parent's DNA. Something along the line of 100 billion mutations is produced each generation according to one study(Ervolino 2014). If each one of those mutations caused a significant change in our phenotype than just imagine how rapidly we would change each generation. It would be impossible to keep track of all the changes. It would also seemingly increase the chances that these mutations could lead to the extinction of our species, since we know that all mutations are not beneficial. It has also been suggested that, on average, each duplication of the human genome includes 100 new errors, leading to the question: why aren't we more different from our parents? It appears as though, while these many mutations do occur, sometimes these genes can become silenced or dormant, causing us no harm but waiting to be unlocked by an external factor from the environment(Ervolino 2014).
Recent discoveries have uncovered that 8% of our DNA comes from viruses and these may have helped us to survive since the beginning of our species existence. This strange twist to our war story has now changed how we view viruses. Some of that 8% of DNA has contributed to the mammalian development of the placenta, because these genes for placenta formation are definitely of virus origin. This vital mutation has allowed mammals, including humans, to survive throughout our evolution. In a way, this means that we would not be here if it were not for viruses, which means we owe them more then they owe us. The irony of that statement is one that I hope my students will be able to appreciate.
Future Applications
If we can revisit the idea mentioned earlier, on the mechanisms of evolution, we can learn much about what our future genomes may look like. Another leading biologist, who recently passed away, Lynn Margulis, had a fascinating idea about the true reason behind why we evolve. She argues that in life, "What begins as parasitism, ends in symbiosis". This is meant to imply that cooperation, or symbiosis, is the driving force of evolution(Karlen 1995). Furthermore, she argued that each organelle started as an infection, and each human cell is a community of onetime invaders. So then what does that make a virus?
According to her research, she believes that a virus is nothing more than degenerated bacteria that evolved from cellular organelles, perhaps from mitchondria that escaped to a semi-independent existence(Karlen 1995). She then goes on to suggest that interactions between parasites and hosts go through stages called, epidemic, endemic, and coming full circle to symbiosis. During the stage of symbiosis the organism can experience two different versions, mutualism or commensalism. During mutualism, they will both benefit from their relationship,. If the organisms happen to experience commensalism, both organisms obtain a mutual tolerance for each other, hence the true meaning of commensalism being, "Dining at the same table"(Karlen 1995). I find this very interesting because it relates to what is happening with the relationship of viruses and humans at this moment in time. Hopefully, this will spark my student's curiosity to wonder about the possibilities of the future and how our relationship will evolve from here. Today, we still do not know where viruses come from, but we are almost positive they are not degenerative bacteria. The common thought today is that they were around before we got here and have figured out a way to survive with the help of a host. Another theory is that through the process of evolution they split off into a reduced form of others forms of life, which possessed a bigger genome; this aligns closely with Margulis' idea. While each of these theories seems logical, if we don't approach viruses with an open mind our understanding may get stuck in place further reinforcing the concept of the "Red Queen Hypothesis".
Speculating about the future evolution of viruses and humans may seem trivial to some, after all we are probably a long ways away from any significant or noticeable phenotypic changes resulting from our interactions with viruses. However, with the possibilities being so vast and diverse, it is hard not to take time to hypothesize what could occur. The unfiltered minds of my students will revel in this opportunity. Therefore, in order to do begin this dream state of ours we can look at familiar viruses for inspiration.
Many of the ideas we know about today have been around for some time, more than 50 years in some cases. Take, for example, genetic engineering. It got its start in 1972, by geneticist Stanley Cohen and Herbert Boyer. It started with them using plasmids, small circular loops of extra chromosomal DNA, in which bacteria carry some of their genes(Naam 2005). The structures that deliver genes into a cell are called vectors and it should not be surprising that most natural vectors for delivering genes of use are viruses. Actually, penetrating a cell is one of a virus' main abilities, making it perfect for this role in the cell. A virus also already has the built-in hardware to complete this task since so much of its fitness depends on the host that it occupies.
However, just like with almost anything, there are some drawbacks. Sometimes the immune system can detect the virus, which could cause the virus to be attacked. The vectors are also not very precise, where often times the virus will just attach to whatever host cell's genome they can reach. This could be disastrous since it could potentially land next to a gene that is vital for survival (for example, a tumor suppressor gene). However, all that being said, as Bioethicist, Arthur Caplan, put it "The notion of enhancement is deeply ingrained in our culture", he continued to say, " we are not the end of evolution- there's no such thing", " we are, if we choose to be, the seed from which wondrous new kinds of life can grow. We are the prospective parents of new unimaginable creatures "(Naam 2005).
Future Examples of Virus Potential
As aforementioned, the unit will provide plenty of opportunity for my students to let their imagination run wild and speculate on the many possible uses of viruses. These moments will be enhanced by some of the examples we will discuss in class. When my students hear about the so-called, "superhero" viruses, they should become more curious about the role viruses play in our lives. The examples we will discuss will be relevant and familiar to them all, helping them to make the lessons we will cover more tangible.
The first example we will discuss is Herpes Simplex Virus. This virus' power resides in the subterfuge and stealth that it has evolved over time. Once acquired, this virus will last a lifetime with most of its life cycle being spent as a master of disguise, invisible to the world. It is said that 80% of the human population is infected, most unknowingly(Smith 2014). HSV is extremely ancient, giving credence to the idea that is has an extraordinary ability to survive as a pathogen alongside humans. Because all viruses need a host to survive, HSV has evolved a way to go undetected in the body, allowing carriers of the disease to transmit the infection without even realizing it.
But, how is this accomplished you might ask?
When the disease is first manifested it doesn't appear as a cold sore, instead you develop a severe sore throat, swollen lymph nodes and a high temperature. These symptoms represent your body responding to the infection. Then, before your body can attack the disease the nerve endings in your mouth serve as the "getaway car", which the virus uses to escape the war in the mouth. Rather than behave as other viruses and reproduce, it slips into the cell's nucleus, twists itself into a small circle of DNA and lies low. This is what is referred to as latency(Smith 2014). It could potentially hide in this location for the host's entire life undetected by the immune system. It's able to hide in this way, because it doesn't manufacture proteins, which would certainly give its location away. When it recognizes a trigger from the nervous system and jumps into action and reactivates, priming it to reproduce. My students should begin to understand that if humans could one day figure out how to adapt these types of qualities, then we too, could potentially possess superpowers.
The next example that students will explore is the effects of the Rabies Virus. This virus' superpower is mind control. Yes, mind control!
Rabies has the ability to colonize salivary glands of its host making it difficult to swallow. This in turn will cause foaming of the mouth, which is a widely known symptom of rabies. The next step of the process involves an infection of the brain, making the host feel higher and higher levels of agitation and aggression(Dr. Sharon Moalem 2007). When animals are agitated and aggressive they tend to bite. When their mouths are foaming with rabies-filled saliva their bites will cause infection; this allows the virus to survive and be transmitted. Survival and reproduction is the primary goal for any organism and rabies virus, has figured out a hell of way to make this happen. One additional anecdote is that this might be where the idea of a Werewolf originated, with its roots in the ancient observations of the rabies virus at work. My students will be able to take this information and imagine what it would be like if humans adapted this ability to make the host feel higher levels of aggression and agitation.
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