defenition of life

suter at VAX.MPIZ-KOELN.MPG.d400.de suter at VAX.MPIZ-KOELN.MPG.d400.de
Thu Feb 24 04:31:18 EST 1994


i hope this discussion isn't getting to boring (it sparked off
several heated arguments here in the lab anyway). i think it is
still interesting ! a basic argumentation for my idea is at the bottom.

paul schlosser wrote:

(much trampled bit on extraterrestrial life deleted)

+>naturally we should keep our eyes open for the unexpected. i will be the
+>first one to admit that our definition is not broad enough, if e.g. 
+>intelligent signals from outerspace would manifest itself completely 
+>independent of nucleic acids (this excludes computers, hehehe). 

+But how can we keep our eyes open if our definition closes them?

your definition probably also excludes putative lifeforms, won't it ?
any definition excludes certain things we have not seen before....
perhaps you could tell us your definition of life ? besides that, if
you are looking for life, you are in fact looking for the unexpected.
the unexpected would have to change our or your (unknown) definition anyway.

+>but as long as
+>no one can show me a putative lifeform that does not adhere to the nucleic
+>acid definition, why should we broaden it ? 

+Because we want a hypothesis for properly designed experiments in the
+exploration of our universe.  If our hypothesis is "life does not exist
+outside of the earth" (the null hypothesis), then, in order to disprove the
+hypothesis, we must 1st define "life" in such a way that does not exclude
+other possible alternatives.

i think such a program should use the nullhypothesis "life, or lifelike 
phenomena do not exist outside of the earth". lifelike phenomena may have 
some of the characteristics created by nucleic acids. SETI is even
more stringent: it only looks for intelligence, of all things ! 

+>computer viruses, extra-
+>terrestrials and chain letters, ok, it is funny to think about, and to look 
+>at them as lifeform imitations, but perhaps you could come
+>up with some arguments WHY they are alive (i didn't follow the discussion
                                     ^^^^^
+>completely, i am sorry. perhaps a summary would be timely ?).

+But we cannot even begin a discussion about whether or not they are "alive"
+until we define what we mean by "alive".  And if the definition inculudes
+nucleic acids then you are by default already excluding these things - the
+argument becomes circular; e.g, you define "life" as incorporating nucleic
+acids, so any alternate definition must be untrue because it doesn't include
+them.

here you misunderstood me: i asked if you could give your definition of 
life ( or alive for that matter). you will see that your way of looking
for life in the universe is also prone to circular arguments !

+How about providing some arguments as to why computer viruses (those that
+can change there own structure/program to adapt) are *not* alive?  If you
+must use "they don't use nucleic acids" in your argument, then you have
+fallen into this circular trap, your eyes are closed to what we might discover
+in our solar system and beyond.

see above.

+You say that if you are shown a real example of something that is "alive",
+but does not use nucleic acids, then you would be willing to broaden the
+definition.  Well, how will you *know*, when shown this thing, whether or not
+it is truely "alive"?  What characteristics must it have, even if it doesn't
+have nucleic acids?  What I am asking of you is to provide the criteria by 
+which you will distinguish between that which is truely alive and that which
+only has the "appearance of life."

this is the core of the argument, which sparked off debate here in my group
also. basically, life has some characteristics: a physical presence (?),
self replicating, information is given on to the (more or less) identical 
generation 'into eternity' etc. 
i then take this description and look at all the lifeforms that i know. and 
what do i find ? hey, they all contain nucleic acids. so perhaps life is
defined by the presence of nucleic acids ? a workable definition, especially
since it seems to be correct in regard to all life that we know, it is short
and concise.

but then you guys come, and say: what about chain letters, computer-
viruses and extra terrestrial nucleic acid free lifeforms ? 
ok, the first two catagories are clearly man-made, and fall in the class 
of 'machines', and are thus completely depenedent on a true lifeform (nucleic
acid containing !) for their survival. especially a computer virus may
mimic life extremely well, but it still doesn't do more than that.
and extra-terrestrial life ? a completely hypothetical point. there is
no indication what so ever that life, or life like forms exist in the universe.
(like supernovas made out of vanilla icecream ! perhaps we should already
include these in our definition of supernovas also ?)

another point, which is rather detached from the above:
somebody also mentioned that this way of looking at life is religiously
based (which may be so....), and he then included computer viruses and
the like also into his spectrum.
but in my opinion, the interpretation of machines as
lifeforms (and vice-versa!) dates back to the rennaisance and following
times, and is not factual, but also highly spiritual (and thus religious).
this line of thought has ended with the cybernetic/organic philosophy, 
to which many scientists have fallen victim. it is especially dangerous,
if you believe that what you are saying has nothing to do with religion.....
 
cheers , clemens !
===============================================================================
Clemens Suter-Crazzolara, PhD
Max-Planck-Institut fuer Zuechtungsforschung
Abteilung Genetische Grundlagen der Zuechtungsforschung
Carl-von-Linne Weg 10,        D-50829 Koeln, Germany
Tel.xx49.221.5062-221    Fax.-213      e-mail: suter at vax.mpiz-koeln.mpg.d400.de
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