una at phy.duke.edu (Una Smith) writes:
[quoted and other stuff deleted]
>>People all too often think of life in terms of a"top-down" approach: going from
>>things with legs or leaves to less complex forms, until they reach viruses and
>>say: "hey, these things are just molecules, anyway!"
>That's right, we're all just piles of molecules which exhibit a
>characteristic (but difficult to characterize) phenomena which we
>call "life" (unless we happen to be "dead"). I don't see what's
>wrong with such a train of thought.
Well, it is wrong because it's rather "descriptional" than essential, or
"fundamental" for life. And it's not characteristic in the highlight of
a "definition of life". Gosh, sometimes I have trouble citing from
my memory but the interested in the topic could probably look up at
"The OSMA Project. Proceedings of NASA" and more specifically at the
conference on the subject of life held in Baltimore, MD in 1968.
The criteria for a system to be considered "living"(on Earth) that the
working group has agreed on at the conference were as follows:
(sorry, not necessarily in the order presented)
1. Life is a characteristic of "individuums".(Unit of life)
2. Living systems are comprised exclusively from the "biogenic" elements
C, O, H, N, S, P
3. Living systems are capable of self-control and self-regulation.
4. Living systems have the ability of self-renovation.(turnover of bio-
5. Living systems are self-organizing.
6. Living systems are self-reproducible.
According to the cited criteria, viruses are indeed alive. (Don't be
fooled by criteria #5 and #6 because viruses are self-organizing and
self-reproducible in a given host(s), which is their "natural" environ-
>>"A material is living if, after isolation, it retains a specific configuration
>>that can be reintegrated into the cycle of genetic matter."
>>- Salvador Luria, 1953 (Virology, 1st Edn)
>>Prescient, wouldn't you say? And describes viruses as organisms as lifepp,
>>succinctly and aptly.
>Prescient of what? Salk had already shown by 1953, I believe, how
>viral cultures could be fractionated into proteins and DNA, and thus
>"killed", but when the components were recombined, the viruses were
>able to re-encapsulate themselves and become infectious again. Since
>you've got the virology textbooks at hand, Ed, perhaps you could fill
>in the facts here. Luria's definition, above, reads to me like a sly
>attempt to say "viruses are alive" without coming out and saying so.
>This definition, as presented here, does not fit most living organisms,
>since if you fractionate them, then recombine the mess you've made,
>the result will not "be reintegrated into the cycle of genetic matter".
>Therefore, Luria's definition may apply to viruses, but it is generally
>invalid and thus inadequate.
I don't think so, "Una". Thanks for the prescious information on
Salk's experiments but it is not on the subject at all. Luria talks
about isolation of "LIVING MATERIAL" and not about decomposing it to
proteins and nucleic acids. Independent of what you ISOLATE--a virus or
a mule, it can be still REINTEGRATED into the CYCLE OF GENETIC MATTER.
So, Luria's definition is GENERAL and thus ADEQUATE.
>>It is quite possible that many viruses evolved from cellular organisms (not
>>living orgs); it is equally possible that there are some viruses around now
>>which descend from bits of nucleic acid that may have been part of the very
>>first self-replicating (acellular) systems - some of the simpler (not
>>primitive) RNA viruses or parts thereof are very good candidates for direct
>>linear descendants of the ancestral RNA molorgs (molecular organisms).
>Is it? Are they? Let's just say we don't know what viruses evolved from,
>but it sure would be nice to find out.
In order to be *nice* and *find out* researchers begin with hypotheses
>[About my insistence on being addressed in the style that is usual and
>customary in this forum.]
>>Methinks the lady doth protest too much.
>We think differently. And, in any case, it's now old business.
It might be old but it's not forgotten.
arseny (an uneducated foreigner)