>>>>> "George" == George Hammond <ghammond at mediaone.net> writes:
George> GH: Thanks for you philosophical notions. As a physicist
George> I still hold out hope that eventualy a hard scientific
George> definition of "Life" will be found. In the meantime, I
George> have adopted as a working definition the criteria that
George> "any being derived from a DNA molecule is a Lifeform" and
George> that all else is non-living. That, at least, seems "hard
George> science" rather than "philosophical".
Well, it's certainly a rigorous definition. It's also overly
exclusive. Most credible people who speculate about alien life forms
believe that they could have a non DNA based life form: RNA, amino
acids or otherwise might do just fine. I think if you address what it
is about DNA that makes you grant it life giving status, then you will
be getting closer to the definition of life.
I think when you attempt to make a mechanistic definition of life, you
go through something like the following. What is it that all the
living things that I know of do? Manipulate the environment to their
advantage. What do they have in common? carbon based, DNA , etc...
Can I abstract these features to account for alien life forms ? ...
The point is that the first part of the question, in my view, has an
inherent philosophical component. You actually can't get down to the
nitty gritty of what it is these things have in common without first
knowing what it means to be alive! So I think the mechanistic
endeavor is structurally flawed.
That aside, I acknowledge the legitimacy of what I think you are
really asking : "Now that we know what it means to be a living thing,
what are the irreducible properties that all of these things share".
But I would be cautious about traversing that road backwards. Once
you have answered the question, I would not exclaim, "So this is the
essence of life!".