From: ian@inf.ethz.ch (Ian)
Newsgroups: sci.nanotech
Subject: Re: Evolution and nanotech
Date: 29 Aug 92 06:24:04 GMT
Organization: Dept. Biochemistry, University of Bristol, UK

In article <Aug.27.22.06.10.1992.6790@planchet.rutgers.edu> tomk@netcom.com (Thomas H. Kunich) writes:
"In article <Aug.26.22.37.40.1992.1563@planchet.rutgers.edu" shearson!snark!pmetzger@uunet.uu.net (Perry E. Metzger) writes:
""
""Normal living systems are DESIGNED to easily evolve. The "blueprints",
""i.e., the DNA, is very flexible; mutations in DNA are rarely as fatal
""to the functioning of a living organism as a single displaced bit is
""in the instruction stream of the average computer program. Similarly,
""the error correcting mechanisms in living things are fairly poor.
"
"If my understanding is correct, this is _completely_ wrong. DNA is
"an exceptionally stable reproduction mechanism. Failures occur but
"on the order of 1-E6 percent. A single failure in the actual mechanism
"of the gene is as deadly as a misplaced bit in any program. Most of
"the gene's information is, apparently, noise. This would correspond
"to changing bit in the memory outsie of the operating portion of
"a program.

This last point depends entirely on the organism.  H.sapiens (us) has an
estimated signal:noise ratio of about 1:1000 which is quite typical of
multicelled organisms, bacteria, on the other hand are much more pressed for 
space inside the cell and have a ratio in the area of 1:2 to 1:10.  Viruses,
at the extreme end of the scale, have ratios sometimes approaching 1.5:1
because they're so streamlined that each piece of DNA has several functions.

(imagine trying to write a program that has one function when run forwards
 and another when run in reverse :-)

"Evolution doesn't work because mutation is easy, it works because
"there has been so much _time_ to work in. Given trillions of nanites
"and plenty of time, there is probably an equal chance of evolutionary
"changes in these programmed creations.

My point exactly, I'm not claiming that the nanites will suddenly become
sophisticated living systems capeable of putting up a good fight for
control of the planet.  Rather I can imagine certain applications being
almost imposible to implement because we can't reply on the replicators
to remain the same for long enough.

To which JoSH comments:
"[Define your terms more precisely.  DNA replication error rates are
" less than one per million BASE PAIRS copied.  This still means 
" a good chance of error for each molecule.
" The whole point of information theory, initially, was to show that
" any desired level of fidelity could be obtained even from a noisy
" channel.  The forthcoming Nanosystems book details techniques for
" achieving similar results in a manufacturing process.  There's no
" magic in it-- you should be able to work some of them out
" yourself from standard ECD methods.
" --JoSH]

I may be showing my ignorance (I usually do :-) but what's ECD ?

[Error Correction and Detection.  Many supercomputers, for example,
 will run so close to technological limits that their memories 
 would be almost certain of losing a bit before any significant 
 computation could be finished.  They might then use, e.g. SECDED
 (Single Error Correction, Double Error Detection) circuitry.
 More common is the single error detect represented by a parity bit.
 --JoSH]