Definition of Life

CACTUSJACKmankin

Critical Thinker
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This has been bugging me for a while, the official scientific definition of life is essentially that all life is cellular. I think this definition is problematic because it is too restrictive, what if there is life that isn't cellular. If we ever hope to look for life on other planets we must have as simple and broad a definition as is possible. So, what is it that separates life from nonlife? respiration, excretion, growth, and so on? yes those are things that nonliving things dont do, unless you count crystals as growth. However, I think there is a single charactaristic that separates life from nonlife... EVOLUTION!!! The capacity to mutate and adapt in order to ensure the survival of future generations. This is what separates the rocks from the corals and the crystals from the paramecium. So, why am i kvetching? because under the current definition viruses are not included as life. There are several reasons for this, viruses are essentially macromolecules and cant copy themselves outside of a host cell. Nevertheless, viruses have DNA and some even have RNA. When the viruses do hijack a host cell and copy themselves, mutation occurs and over the long term evolution occurs. How can something that clearly can evolve not be considered living? A very interesting fact about viruses is that they can be artificially created in the laboratory and if they are a form of primitive life it vastly broadens the potential for life in the universe.
 
Robotic systems currently are used to build things with tremendous precision. It wouldn't be too difficult to imagine (in the not to distant future), a machine that repairs, grows and/or modifies itself - sentience aside. It could technically be designed to evolve without higher level thought. Also, what if nanites were engineered to evolved. Doesn't seem appropriate to consider evolution as the sole distinguisher between life and nonlife.

>added nanites ref
 
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There's a big difference between finding a ball of protein that has genetic information and creating a computer program whose code has an evolution mimicing algorithm.
 
CACTUSJACKmankin said:
There's a big difference between finding a ball of protein that has genetic information and creating a computer program whose code has an evolution mimicing algorithm.
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I agree there is a big difference between the two but it’s still evolving nonetheless. It all depends on how tight and what definition of evolution you’re using.

Check out Cecil at Straight Dope: http://www.straightdope.com/classics/a971212.html
 
I think it was Dr. Adequate who posted a definition I rather liked. Something like "chemicals that induce their own synthesis." though I'm sure I'm mangling it. I hope he shows up.

Of course, I'm not sure I like it to the exclusion of others. I like the really broad definitions of life that include things like computer viruses and whatnot. But that's me.

Anyway, I think that in approaching this question the first step is to ask, "What is meaningful about saying something is alive?" and proceed from there.
 
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