Member (Idle past 779 days)
Message 123 of 132 (481795)
09-12-2008 4:10 PM
In any question over the dividing line between life and non-life, we first need to discuss what life is. Arbitrary assertions of "that's alive" and "that's not" are uselessly subjective and carry a discussion nowhere. We need a set of properties that all life posesses so that we can identify any specimen as "alive" or "not alive" by a comparison to those criteria only, and not subjective preconceived conclusions. This is the way that all of taxonomy works, by classifying organisms according to their properties.
So what defines life?
1) All life reproduces, though the manner of reproduction varies significantly (sexual, mitosis, etc).
2) All life metabolizes energy from its environment, though the method again varies significantly (photosynthesis, consumption of organic matter, etc).
3) All life responds to stimuli (though all forms of life do not respond to all stimuli).
That's about it. We know that all life we've ever seen is organic (carbon-based), but we don't know whether that's the only possibility, so there's no reason to include that in the definition. We know that all examples of life we have ever seen came from pre-existing forms of life, but we know that it's possible for life to arise from non-living matter (whether spontaneously or directly created by an intelligence), despite the fact that the manner in which this occurs is still unknown, so saying that all life comes from pre-existing life is needlessly exclusive - if we find a specimen that meets all of the other deifinitions of life but which was not spawned from a pre-existing life-form, defining the specimen as "not alive" would be arbitrary and subjective.
Let's take a look at some examples of living things. We all know that these things are alive, so there should be no controversy.
1) Human beings. Obviously, we're an example of life. We reproduce, we metabolize energy from our surroundings, and we respond to a great deal of stimuli.
2) An oak tree. Trees reproduce, though the method is compeltely different from human reproduction. They metabolize energy, though again it's in a completely different manner from ours. They respond to stimuli, though very differently and over longer timescales than we do - trees grow towards light, for example.
Let's look at a few things that are not alive.
1) A desk. Though it can be made of once-living matter, desks cannot reproduce, they do not metabolize energy, and they do not respond to stimuli.
2) A rock. Again, rocks respond to no stimuli, do not reproduce, and do not metabolize. They are inert.
Suppose somewhere (deep in the ocean, or maybe on Io, it doesn't mater) we find something intresting - a complex crystalline object that grows towards heat sources, and uses that heat energy combined with the surrounding matter to grow. After enough growth, peices of the crystal will break off due to its size, and the peices will continue to grow, metabolize the heat, and respond to the presence and absence of heat.
Is this object alive?
By the earlier definitions, yes it is. It responds to stimuli (heat), reproduces (by a version of budding), and metabolizes energy from its environment.
But lets say we find a specimen that's a bit less clear-cut. This next example reproduces, but needs a host organism in order to do so. It metabolizes energy only within the host. It responds to stimuli only by the presence or absence of its host, and irrevocably ceases metabolization and reproduction if removed from the host.
This would loosely meet the conditions we set earlier. But what did I just describe?
Did I describe an immobile parasite with a life-cycle compeltely dependant on host organisms to feed and reproduce? Many parasites are compeltely dependant on their hosts for metabolizing energy (many "hijacking" the host's own digestive system so that the parasite can simply absorb the already-digested nutrients) as well as reproduction (there are species of parasitic wasps for example that reproduce only in the bodies of spiders paralyzed by their sting), and respond to stimuli only by being "active" in their adapted environment.
Or did I describe a virus like HIV? Viruses require host cells to reproduce and metabolize energy ("hijacking" the machinery and even DNA of the cell to perform both functions), and again only respond to stimuli in becoming active inside of a proper host cell. When outside of a human body, the virus quickly "dies" due to an inhospitable environment, irrevocably losing the ability to function even with a host cell.
Most people would identify a parasite as "alive." Yet for viruses, their status as "living" or "nonliving" is debateable. Many people insist that viruses are not alive becasue they are not composed of cells, but that's an arbitrary classification - why must all life be cellular even if it meets all of the other conditions for being defined as alive? AOKid claims that viruses are not alive outside of a host cell, but why, if they can still become active when placed in the environment of a host cell where they can function? A better definition of "dead" in this case would be that the virus can no longer become active, as is the case of HIV when out of the body. At the very least this claim is an admission that viruses are "alive" inside of a host cell, meaning they are still an interesting example of something that doesn't fall neatly into the "alive"/"not alive" categories. In a bit of irony, you could say that in this instance AOKid is even admitting that the nonliving matter of a virus becomes alive in a cell, and nonliving matter becoming alive spontaneously is the very definition of abiogenesis.
What about prions? Even simpler than viruses, prions are complex proteins that essencially turn other proteins into additional prions. They're responsible for such things as "Mad Cow Disease," and basically contradict everything we knew about reproduction. They definitely reproduce, but they don't really metabolize and can't really be said to respond to stimuli any more than a bicycle - if the structure is broken, neither continue to function.
What about sperm? They don't directly reproduce, they're a means for reproduction - sperm do not beget additional sperm. Yet they metabolize energy and respond to stimuli, but they don't metabolize from their surroundings, they don't have "food" or derive energy from photosynthesis. They can be said to "die" due to temperature or Ph differences, becoming inert. Most people would count sperm as "alive."
It would seem that the question of "living" vs "nonliving" is not the binary yes/no, black/white classification it is commonly assumed to be. Many things in the world meet some of those conditions, but not all of them. I wouldn't say that prions are alive, certainly, but I would say they are more alive than an inert rock. I would say that viruses are more alive than prions, but less than bacteria or plants or animals. It would seem we have a spectrum at the simple levels of life, a gradual progression from completely inert matter to simple chemical compounds that meet some of the conditions of life and leading eventually to truly living things.
Discussions regarding abiogenesis are useless without defining what life is. Subjectively claiming "viruses are not alive" or "sperm is alive" are nothing more than bare assertions without the qualification of the properties that define life. And when we come up with such properties, so long as we maintain objectivity and do not arbitrarily restrict our definition to extant forms of life, we inevitably find that the line between life and death is blurry.
Member (Idle past 468 days)
From: The city of God
Re: Resurrection of topic due to interest
This is not true. Blood cells have an average life of 4 months. You are saying that when one of my blood cells dies, I die.
More fallacies doku. This is a total strawman argument. Yes bood cells die all the time. Blood cells are organisms. And like all organisms, they die. I guess you don't know the difference between a multicellular organism and a single celled organism.
Science has had problems trying to define death because new technologies have extended life past previous definitions. New definitions rely on the cessation of brain activity and function. What is to stop science from keeping a brain alive indefinitely?
Death....................and God for that matter.
Biological science has problems definining alot of things. That's why they can fool people like you.
The analogy still holds. The machine's functions stop. The cell's functions stop.
The analogy doesn't have a leg unless you agree with itelligent design. With no intelligence, no design changes, and no ability to fix the failing machine. The medical field is wonderful evidence of intelligent design. But even the most intelligent human designer cannot prevent death indefinitetly.
Actually yes I do. there is scienctific evidence for it. Here are 2 examples:
1. The hydra is a radially symetrical organism ranging in size from 1mm-20mm. Hydras do not age. They are biologically immortal.
I think your fallacies are immortal doku. Now you equivocate aging with dying. All hydras die. They just don't age.
2. Did you know that some cultivars of grapes are clones that have existed for thousands of years? Did you know every Granny Smith apple comes from a single chance plant that was grown in 1868 in Austailia by Maria Ann Smith? You cannot grow a Granny Smith or any other variety of apple from seed. Wouldn't you agree that is immortality?
Nope. Fallacy after fallacy! I guess tulips and potatos are immortal too? They aren't grown from seeds either. Maybe we shouldn't be so hard on Mickey D's for frying all those immortal taters. Who knows, It seems to me that life expectancy started increasing about the time McDonalds came into the world. Maybe the potatto is the tree of life! :laugh::laugh:
The telomeres do not have to be infinitely long, just infinitely extended.
This one takes the cake doku. I guess every 40 years or so we will have microscopic surgeries to have telomere extensions for all of our 6 trillion cells. Yes, He has the faith!
And you guys think creos are religious?
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