From: Robert J. Bradbury (bradbury@aeiveos.com)
Date: Thu May 09 2002 - 01:08:54 MDT
On Wed, 8 May 2002, Eliezer S. Yudkowsky responding to my comments wrote:
> One mass extinction every hundred million years may not be enough
> statistical regularity to produce adaptation. If there were zones of mild
> and increasing radiation, then sure, you'd get species evolving more
> radiation tolerance and gradually moving into more and more hazardous
> niches. One mass extinction every hundred million years seems more to me
> like survival of the stable than survival of the fittest, and survival of
> the stable doesn't produce complex functional adaptation.
I'd generally agree with this. The problem is that the 100 million year
figure is stellar/gas density dependent. Closer to the center of the
galaxy you are going to get toasted more frequently. It would only
take a few toastings over a few million years (seems statistially
probable) to bump you up into the radiation tolerant gene set.
Now there is a problem with this -- the radiation tolerant gene set
may be the non-evolving geneset. So there may be lots of life
on near galactic center planets -- its just very primitive.
One wild card is whether or not Deinococcus is a "typical" example.
You may get radiation tolerance as a side effect of dessication
tolerance. So individual planetary conditions might produce
gamma ray burst/hypernova tolerance. It also doesn't seem implausible
to have genome hyper-maintenance programs that can be invoked
"on demand" but are normally inactive [given the amount of junk
DNA present in most mammalian and plant species]. The SOS
response program in bacterial genomes (hyper-mutation in response
to poor survival conditions) would seem to be an example of
how one fits the rate of evolution to the environment.
The bacterial genomes we are most familiar with are those that
would tend to evolve fairly quickly (above ground, moderately
low radiation, "normal" environment or in-people/in-lab conditions).
We have very little knowledge of the genetic programs of bacteria
(or other organisms) that exist in those environments we haven't
managed to reproduce in the lab. The capabilities of organisms
that have evolved to live in/evolve on geological time scales
may be quite surprising to us.
Robert
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