Viruses
Offline Ok so I'm studying for a ridiculously boring class, and I came across a line in our power point that said viruses are NOT living.
I know I've heard people say that before (maybe my doctor?) but it struck me as odd. Viruses are made of DNA, RNA, protein. Doesn't that in itself make viruses alive?
After a little research, I found that the question of whether viruses are alive is a debated topic. Due to the fact that it has no cellular components, its inability to replicate itself unless in a host cell, and lack of metabolic properties, many scientists/doctors have concluded that it is not living. Isn't that a bit rigid? In the past 100 years we have discovered a huge amount of information pertaining to genetics, evolution, etc that has greatly altered our understanding of the process of living. My problem is that some schmoe decided that in order to be alive you needed cellular components. Some other guy decided that because antibiotics can't kill viruses, and the name antibiotic comes with the assumption it kills life, then viruses cannot be alive.
I say antibiotic is a misnomer, and I also think that viruses should be considered alive. Some doctors have no problem saying that you can "kill viruses" right?
There are theories that viruses used to have cellular components that could survive without a host, but evolved so that it needed a host cell to survive. I don't know why little things like this irk me so much, but I can't grasp how the science field can prove that arbitrary definitions are meaningless and then turn around and take some rigid definition of "living" and decide that something made completely from the building blocks that create organic matter is non-living. It moves, interacts with its environment, and can make copies of itself. Is there something I'm missing?
I feel like this could potentially be an important hurdle to jump, due to the studies about how viruses affected the evolution of life.
On a side note, I stumbled across horizontal gene transfer in the process of this research, and I can't believe how interesting it is. I don't know how anyone could even question evolution after learning about this stuff. I know a lot of you guys are probably schooled well on HGT, but genetics is an unstudied area for me, so I find it amazing.
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But my opinion is - memorize it for the test.
Then - go do your own research. I have noticed a number of differences of opinion amongst the biologists. Stick 10 biologists in a room and you can find 1,000 different opinions. It is one of the things that lay people - creationists in particular - have a difficult time with. Doesn't bother me that biologists (and other scientists) have differing opinions even in their own field. Nothing is written in stone, after all. Listen to them all, memorize the one the particular professor wishes you to herk back on the test, then make up your own mind.
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The way I see it, the issue is that people are trying to put a line down the middle of a seamless progression. It's like with human reproduction, it's practically impossible to say that at a certain point in development what is in the womb becomes 'alive.' Black or white classification doesn't work very well in either of these situations, because the subject matter is too complex.
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The problem is that "Life" is often seen as an either/or proposition, but it's not. If we could watch a video of the very first life on earth coming into being, it would begin with the precursors of replicators -- perhaps clay crystals -- and progress through to the precursors of RNA, whatever they might have been. RNA probably didn't just spring into existence fully formed. It was probably the first replicator with a structure stable enough to become dominant in the environment. As we watch the video, we would see pre-RNA that began to look more and more and more like RNA, until one day, it would be obvious that RNA was here.
It's the same with developing life. As life developed, it acquired more and more properties we now think of as "living," including cell walls, homeostasis, and rudimentary metabolisms.
Think of watching the sun rise. The sky starts to get light long before we see the sun, and it's really difficult to pinpoint the exact moment when "daybreak" hits. We give it an arbitrary time... we say, "It's officially day when all of the sun has passed the horizon," or something like that, but in reality, there's no distinction between that moment and the one before it in terms of the rotation of the earth or the presence of light. It's a gradual, continuous process.
Viruses are an intermediate. They have some characteristics of "life," but not others. It's best to just rid yourself of any notion that life is an on-off switch and think of it more as an arbitrary definition we use to describe a particular incarnation of replicators.
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I think I could buy that, and you and vaulting bassist both hit on some of the same key points so thanks.
My one beef is that the characteristics of living mammals is wildly different than that of living plants, single-celled organisms, reptiles, etc.
Why can't we just call a spade a spade? I feel that from a functional standpoint, anything made from organic material that has a finite span of existence (LIFE span?) that can interact with its surroundings, replicate, adapt, and evolve is alive.
I know this can be a slippery slope to a philosophy discussion, so I'm just going to stop haha.
I've always felt that the definition of life crucially rests on the basis of whether or not something evolves. I consider viruses alive for that reason. For me, the correct boundary test-case are prions, which are proteins that contagiously 'mutate' into harmful configurations, such that they usually end up killing the organism. At first glance, it appears that prions may be 'as alive' as viruses are. However, crucially, prions do not themselves actually mutate in a heritable fashion, and so they do not actually evolve. Viruses, on the other hand, do.
Another few interesting test-cases are: Fire, crystals, automobiles (appear to have 'metabolism'), stars, et al.
None of these things actually evolve.
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This is from my current life science textbook explaining why the majority of biologists do not consider a virus alive:
1. Viruses are acellular. One criterion for classifying organisms is how many cells they have. Viruses have none.
2. Viruses are totally dependent on other organisms. Not only must a virus enter a cell of its host to reproduce, it is utterly dependent upon the host for energy, raw mate- rials, and the machinery to make proteins.
3. When dried, some viruses form crystals—a characteristic shared with many obviously nonliving substances such as protein, salt, and sugar. No living cells form crystals when they are dried.
I am very new at this whole biology thing, but from what I can tell, based on the list of criteria that indicate a living organism, the above makes sense.
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My point is that the classification system is flawed. Like I said it is thought that viruses were in cell form before they evolved into an acellular entity. Is chlamydia, which is a cell and classfied as a virus, alive?
But like I said, this process is only occuring now due to natural selection. Viruses (most likely) were able to reproduce without a host. Their need for a body to reproduce actually proves my point because they acquired that characteristic through evolution.
Touche, text book writer.
One of the reasons I hold to the 'it must evolve' criteria for life is that we may eventually discover bizarre life on other planets. If biology textbooks stick to an Earth-centric definition of life, then so much worse for those textbooks. If the criteria for life cannot correctly detect something 'alive' that is alien to us, then the criteria are fucked.
1. So fucking what? Who says life has to be cellular? Tell that to the non-cellular alien life that is invading our planet as we speak (a hypothetical science-fiction scenario; don't worry, I don't own any tinfoil hats).
2. Animals are totally dependent on other organisms. Not only are animals dependent on plants for oxygen, they are also utterly dependent on the consumption of other life for energy, raw materials, and the machinery to make proteins. Wait, so animals aren't alive?
3. When frozen, cellular life forms crystals. So what? How is being frozen (or dried) a criterion for life?
The big challenge of the idea of 'life' is the incredible complexity and adaptation that living things display without apparent conscious creation. The reason textbooks (highschool or early university, but not graduate level) rely on such simplistic definitions of life as metabolism, growth, cellularity, etc. is because of mere correlation, not causation. It so happens that most life on Earth shares cellularity, but so what? Why is cellularity a pre-requisite for life? They never explain. Such textbook definitions are designed to bypass the difficult questions by providing all the *accidental* characteristics that happen to belong to what most people accept as 'life'. Using such a textbook definition as an 'official' definition of life is a cop-out and begging the question of the *necessary* conditions for life.
Here's an interesting and challenging question that someone with a 'definition of life' must be able to answer coherently:
Suppose we eventually send out a space probe that discovers a planet that actually *does* contain alien life. How would the space probe know the difference between life and non-life? Perhaps a simple machine cannot do the job. Nevertheless, the machine can gather information and send it to Earth. Suppose the probe sends information about two substances, A and B. Substance A happens to be *actual* alien life, whereas substance B is not. What information about A would convince a human on Earth that A is life and B is non-life?
For me, the answer is fairly simple: Does A actually evolve? If yes, it's life. If not, it isn't. The only kind of alien substance that I can imagine calling 'life' *must* be capable of evolution, or else I cannot fathom how it is possible to call it 'life'. I simply don't see how 'cellularity' or 'when it dries it doesn't form a crystal' has any relevance to the question of life. Evolution is the key.
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I agree one hundred percent. Evolution is the best definition of life. Under this definition, DNA/RNA are really the ONLY living things. Cells and the organisms that there cells create are simply their vehicles. Virus can jack other DNA/RNA's vehicles. They are the only truly living things. The only truly evolving things in biology.
In the classic definition, viruses are considered rouge genetic material. Insignificant fuck-ups that just wreck havoc. I think they deserve more than that.
Prions on the other hand. They are just creepy, insignificant fuck-ups.
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Perhaps I should have shared what that particular textbook says about life. Here is the criteria they share to determine living organisms:
◆ are highly organized, complex entities; ◆ are composed of one or more cells; ◆ contain a blueprint of their characteristics (a genetic program); ◆ acquire and use energy; ◆ carry out and control numerous chemical reactions; ◆ grow in size and change in appearance and abilities; ◆ maintain a fairly constant internal environment; ◆ produce offspring similar to themselves; ◆ respond to changes in their environments; ◆ may evolve into new types of organisms.
You all have great points and questions ~ natural, I never thought about texts being 'earth-centric'. Once I feel confident in my understanding of basic biology, I may be able to participate in some of these threads ~ The textbook I am using right now is 'associates' level...very introductory ~ since I am in school for a business degree, I don't anticipate being involved in many more science classes...I will have to continue my interest in biology here
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