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Alu sequences and human evolution

RYBICKI, ED ED at molbiol.uct.ac.za
Wed Jul 20 03:54:38 EST 1994

> 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 
of your
> 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 
periodicities in
> 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 
presence of
> 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 
what sHe
> is fishing for.
>  Since the genetic code appears to be essentially universal I 
think that
> 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 
> required?

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)        |

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