Text 580, 71 rader
Skriven 2004-10-30 16:55:00 av Catherine Woodgold (1:278/230)
Ärende: First Mutation Was Biggis
=================================


Right at the very beginning of Life, there must have
been a sudden, substantially beneficial mutation.

Ever since then, evolution has progressed in steps
of a variety of sizes:  big, medium, small, tiny.
Mutations benefitting organisms by a fraction of a 
percent in probability of survival and reproduction
per generation gradually propagated through populations
and arguably made up, collectively, the bulk of
the progress of evolution.

But the very first Life had to face a hurdle none of
the rest of us has had to face since:  direct competition
from non-Life.

It's not that the act of replication on the 
primal Earth was necessarily all that difficult:
I wouldn't know -- I wasn't there.  But whether it
was easy or hard, likely or unlikely, the conditions
for replication came about, and replication happened.

The first molecule to replicate had to have been created by some
process other than replication.  Here I'll call all other processes
which create molecules "spontaneous generation" (SG).

But if one strand of RNA -- or whatever the first Life was made of --
spontaneously appeared, likely other such molecules were also being
spontaneously generated, and were competing with the first Life
for resources -- in this case, free RNA bases.

Suppose one replicand had, by good fortune, some characteristic
that made it one percent better at surviving and
replicating than the other, run-of-the-mill, 
spontaneously generated molecules.  Well, that one percent
wouldn't do it much good.  OK, it might happen to have
a dynasty of 4 molecules instead of 3.  Big deal.
It would still die out.

The trouble is:  the descendents of that first would-be Life
had only one way of being created:  by replication.  But
the rather similar molecules they were competing with had
two ways of being created:  replication, and spontaneous
generation.  A mere one percent advantage would be practically
nothing in the face of being outnumbered by the random
RNA strands continually being created.

If plenty of free RNA bases were available for replication,
it seems inevitable that some of them joined together to
spontaneously generate new strands.  SG must have
happened at least once, for the first ancestor of
life to appear.  If there was some mechanism preventing
SG from happening again, so that the descendents of that
first molecule had no competition from further spontaneous
generation, then I would call the appearance of that first
strand the major mutation I'm talking about.  It had to
be something that separated the wheat from the chaff, in
some way:  the appearance of a molecule which, while it
would inevitably face competition from copies of itself,
had some definite advantage over all spontaneously
generated molecules in the vicinity.
--
Cathy
---
ū RIMEGate(tm)/RGXPost V1.14 at BBSWORLD * Info@bbsworld.com

---
 * RIMEGate(tm)V10.2á˙* RelayNet(tm) NNTP Gateway * MoonDog BBS
 * RgateImp.MoonDog.BBS at 10/30/04 4:55:54 PM
 * Origin: MoonDog BBS, Brooklyn,NY, 718 692-2498, 1:278/230 (1:278/230)