Joe Gwinn said:
DNA is actually pretty stable, if properly packaged. They got DNA from
Ötzi the iceman, who had been in the glacier for 5,300 years:
<
http://en.wikipedia.org/wiki/Ötzi>
Not under constant use, of course
Biological systems are robustly error correcting on all levels. On the
highest level, evolution simply discards unsuccessful DNA: it dies.
On the lowest levels, DNA is patched, copied, bundled and moved by
numerous cellular proteins (all of which are, themselves, constantly being
smashed up, recycled and re-synthesized directly from the very DNA they
serve; as far as I know, *no* non-structural chemicals inside the cell are
permanent, they are constantly being remade!).
Suppose a DNA mistake occurs anyway. Structural errors simply throw a
wrench in the works; the cell sacrifices itself for the greater good
(apoptosis). If the result is a coding error, the associated proteins or
whatever will change; most of these changes (that don't already result in
destruction) are apparently fairly innocuous, as there are a lot of
positions in a lot of proteins which have little functional impact.
If one of those changes happens to relate to immune system codes, however,
the body's immune system comes in and snuffs it out. Cancer is constantly
developing in our bodies; almost all of it fades out on its own or is
attacked. The unlucky ones that sneak past those defenses, and find the
mutations that allow unlimited growth, are the only ones we have trouble
with today.
The most striking difference between cells and automatons, besides the
complexity (as far as I know, no one has yet engineered a computer
operating system where the code constantly rewrites itself, from a
parametric, self-modifying source, as it copies and executes that very
code), is the simple fact that we don't have a freaking clue how to do it
efficiently.
Consider the amount of raw materials and power required to operate a
machine shop, continuously, turning out parts not just for the robots
doing the work, but replacement parts for the machines making them. Then
consider the amount of power required to operate the foundry to melt and
recast the metal parts, off-cuts and waste. Finally, consider the amount
of power required to operate a complete chemical recycling plant, to
recover metal from the inevitable oxides generated in the foundry, machine
shop and from general corrosion, plus recycling and reformulating all the
lubricants, fuels, and other waste products produced in the process.
And now try running your self-replicating factory from a robust power
source like thermocouples!
The turnover of most cells apparently is on the order of 10 years,
http://www.timeshighereducation.co.uk/198208.article
but the most rapid are white cells (not mentioned in the article, but as I
recall, they're just a day or two) and intestinal lining (a few days),
while the oldest don't reproduce at all. So, of course, it would be quite
reasonable to build something like a solar Stirling engine, which wears
out frequently due to poor materials (suppose we're recycling the same
1020 mild steel for everything structural, no abrasion-resistant alloys,
no lightweight alloys, no bearing metal) and poor lubricants (which we're
recycling and reforming, so must be simple, something like mineral oil
let's say), but because there's a million of them each producing a little
bit of the power needed, and a thousand are constantly being rebuilt, who
cares? That's 99.9% uptime right there. Oh, and that's the other
biological advantage, strength in numbers...
Tim
