> In article <MAILQUEUE-101.940719103729.256 at molbiol.uct.ac.za>,
>ED at molbiol.uct.ac.za ("RYBICKI, ED") writes:
>> "..Read first, formulate theory later.."
>> Thank you Dr. Rybicki for your post response. I agree with some
> criticism but have a problem with your attitude unless you are
> to be humurous.
Wee--eeelll....flames are a bit easier to take sometimes when
couched in a semi-humorous vein.
> cataclysmic theories can explain rapid extinction, ... One thought
is that the same comets or
> asteroids that may have caused extinctions could have also carried
> "XNA" to earth which could explain the rapid appearances of new
> order" traits
But HOW...? How does the XNA get off the comet/meteor/whatever?
Atmospheric entry is a rather traumatic process (as Shoemaker-Levy 9
is dramatically demonstrating in Jupiter's atmosphere), so how does
sufficient XNA of sufficient LENGTH to do anything, survive long
enough to get INTO anything? Because transformation is a tricky
process at the best of times; XNA being licked off a cooling rock
fragment doesn't make it very high in the probability stakes for
getting into the germline, and as for VIRUSES coming off comets...!
I know Fred Hoyle likes the idea of influenza epidemics tying in
with meteor showers (he thinks they sift gently to earth), but there
are a number of HUGE holes in his theories, not the least is that we
KNOW where "new"'flu viruses come from: birds, and pigs, and Chinese
mixed farming techniques. The existence of virions presupposes that
there was something that they infected in the first place - and
given that the Oort Cloud (where most of our comets come from) is
not exactly a hospitable environment in terms of atmosphere,
nutrients and temperature, it is EXTREMELY unlikely that there is
anything there for viruses to have infected, in order to get made in
the first place, in sufficient quantities for them to do what you
want them to do. Also please realise that - lacking evidence to the
contrary - that cross-phylum viral infections on Terra are rare
enough, despite the fact that everything on this planet is probably
more closely related to each other than to anything off it, that the
possibility of anything from OFF-planet being able to infect
anything here is HUGELY unlikely. And there is the time-frame
question...there is no evidence that, even under ideal conditions,
viruses can survive the time span given in geological ages necessary
for any given comets to have any probability of getting near enough
to Terra to shed any virus on us.
You are right in pointing out that one postulate does not
> require the other, however, inorder to explain certain
> the punctuations of evolution I am tying the two ideas together.
> viral role in evolution connected to the "idea" that some viruses
> carried by comets).
Catastrophic population collapses and rapid selection from a small
population base could do it, whether caused by celestial accidents
or not - WITHOUT invoking viruses. And endogenous retroviruses can
be induced to pop out under stresses like increased radiation
> In regards to the second general idea I have read that :
> 1. Studies of the Murchinson meteorite from Australia have shown
> presence of amino acids and nucleotides.
> 2. Spectrophotometric studies of Halley's comet showed the
> organic molecules.
It is an ENORMOUS step from organic molecules - which in the case of
Halley's were SIMPLE organics - and even AAs and Nucs, to proteins
and oligonucleotides. Like a billion years or so of chemical
evolution, in an environment with far more highly concentrated
nutrients and of far higher temperature (=faster reaction rates)
than are to be found in interstellar space.
> I also would like to debate the your comment that PCR
> cannot be used on meteorite material because one would not know
> is fishing for.
> Since the genetic code appears to be essentially universal I
> using a shotgun approach with universally recognized sequences
> potentially amplify any XNA present in a properly prepared
> sample. The question is; what is the minimum oligonucleotide
Alas, some naivete concerning the undoubtedly wonderful technique of
PCR...yes, one can randomly amplify up DNA/RNA - it's done all the
time in the RAPD techniques. However, one needs the assurance of a
certain minimum target genome complexity AND length of nucleotide
sequence - like 200-500 bases or so. Viruses probably do not have a
necessary genome size - except for big chaps, like the T-even
phages, and pox- and herpesviruses - to guarantee that RAPD-type
primers would work on them, EVEN if (and it is a big if) their
genomes were miraculously unfragmented by whatever clestial process
deposited them on a rock on Terra.
So, in summary: I have no problem with viruses as an agent for
accelerated mutation/evolution; retroviruses and
retrotransposons/retroposons are demonstrably present in just about
every organism looked at from Archaea to people - but YOU DO NOT
NEED to postulate any other origin for viruses other than our own
little terrestrial biotic soup. Without a great deal more
convincing evidence (and Sir Fred don't make it as an authority
concerning viruses), you will simply be detracting from your central
thesis by dragging in comets and the like, which should already (as
pointed out elsewhere) have been shaved off by Occam's razor, in the
interests of parsimony of postulates.
Good luck, post workup when ready!
| Ed Rybicki, PhD | Well, I tip my hat |
| (ed at micro.uct.ac.za) | To the new constitution |
| Dept Microbiology | Take a bow for the new revolution... |
| University of Cape Town | Then I get on my knees and pray |
| Private Bag, Rondebosch | We don't get get fooled again... |
| 7700, South Africa | |
| fax: xx27-21-650 4023 | - Pete Townshend, 1972 |
| tel: xx27-21-650 3265 | (Won't get fooled again) |