From: una@phy.duke.edu (Una Smith)
Newsgroups: bionet.molbio.evolution
Subject: Re: are viruses alive?
Summary: What is life anyway?
Keywords: evolution life organism virus
Date: 21 Jul 92 23:04:03 GMT
Organization: Duke University Physics Dept.; Durham, N.C.

Ed Rybicki <rybicki@uctvax.uct.ac.za> writes, first paraphrasing me:

>Viruses are alive because they EVOLVED from living organisms?  I think we need
>a definition of organism here:
>"An organism is the unit element of a continuous lineage with an individual
>evolutionary history."
>- Salvador Luria, JE Darnell Jr, David Baltimore & A Campbell; General
>Virology, 3rd Edn.

It would be helpful if you would include page numbers when quoting from
books.  I disagree, however, that a definition of organism is needed;  a
good definition of life certainly _is_ needed.  I tend to agree with
Harold Morowitz's definition of a living organism, and I'm looking 
forward to reading his new book, which I haven't had the priviledge of 
reading in manuscript.  


>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.


>"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.

>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.


[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.

	Una

-- 

Una Smith   una@phy.duke.edu    School of the Environment
                                Duke University
                                Durham, NC  27706