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From: sa209@utb.shv.hb.se (Claes Andersson)
Subject: Re: "What is Life?"
Message-ID: <1995Feb6.133515.18880@gdunix.gd.chalmers.se>
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References: <3ghi64$osf@hptemp1.cc.umr.edu> <3gje3b$t4b@engnews2.Eng.Sun.COM> <1995Feb1.194004.17652@gdunix.gd.chalmers.se> <3gv2bf$5hm@engnews2.Eng.Sun.COM>
Date: Mon, 6 Feb 1995 19:53:51 GMT
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holtz@netcord.Eng.Sun.COM (Brian Holtz) wrote:
>In article <1995Feb1.194004.17652@gdunix.gd.chalmers.se>,
>Claes Andersson <sa209@utb.shv.hb.se> wrote:
>
>>>>: Life is the ability to reproduce and evolve.  A more involved
>>>>: definition is required if we want to be able to tell living things
>>>>: from inanimate, unborn, and dead things. An entity can be
>>>>: considered alive if and only if it 1) is of a kind that usually can
>>
>>Hmm.. I like this! What a rule! The word "usually" is generally somewhat
>>funny to find in a rule :-)
>
>So the Laws of Thermodynamics aren't "rules"?  ;-)

 They are, very well. I must admit that I wrote that a little fast. I see what you mean
but I still don't agree on it since I consider reproduction and selection as TOOLS
for obtaining life. They are the only known and reasonable tools but still they can't
be used as definitions.

>
>>>>: reproduce and evolve, and 2) has achieved independence of a parent's
>>
>>Parent's? Is that really something that should appear in a fundamental description
>>of life?
>
>Please read what you excerpt.  I defined two terms, "live" and
>"alive".  My definition of 'life' did not mention parents.
>
>>A definition of life must not require life, it will be a paradox!
>
>1. My definition of 'alive' (not 'life') has no such requirement.  I said
>   "a parent", not "the parent" or "all parents".  That is, you don't
>   have to have a parent to be alive.
>
>2. I never said that 'alive' is part of the definition of 'parent', so
>   there is no circularity whatsoever.
>

  Okej, I see. I read it but since I generally don't make any distinction
between alive and life myself I failed to noticed it somehow. Anyway,
the same as I've said: I consider aliveness to be a required feature of
a lifeform and that something that is alive is necessary a lifeform.


>>Of course, most life as we know it corresponds to these three points but
>>it is more like an observation of general features of life.
>
>Once again, these are three criteria for aliveness, not life (which is
>about reproduction and evolution).  Further, to refine these criteria,
>I'd be interested to hear about a living thing which is excluded by
>them, or an inanimate/unborn/dead thing which is included by them.

 Do you suggest that there are lifeforms that aren't alive? Or alive things
that aren't life? Not really... A virus should qualify as such a lifeform but
isn't that quite far out? Are you talking about viruses as lifeforms that lack
aliveness then? The two of them are the same, the things you refer to as
characteristics for life (reproduction and evolution) is firstly quite strange
since reproduction is a evolutionary operator, they are not separate. But I
do see what you mean and yes, evolution is probably the only way to
obtain life but just as the example with the car, they merely tools and inductive
rules. As soon as you find a lifeform that isn't evolved (not that I think there
are any, or at least inderectly evolved like robots which are constructed by
humans who have evolved) it will be falsified. A general simple rule like
that one I'm advocating is on the other hand not possible to falsify since it
would define aliveness which is required for something to be a lifeform.
Isn't it a reasonable way to categorise a life process?


Claes Andersson. University of Bors. Sweden
