Re: Ancient Radiation levels

[Harald Weiss <weiss@ki.comcity.de>]

Martin Fraser schrieb:
> 
> Actually, Harold, this is I believe a common misunderstanding of Darwinism.
>

Dear Martin, Andrew, Bruce, Brian, ...

please apologize first my late answer, I've been off for a while.

I guess I'll have to write a few more sentences to make myself
understood. 

In my opinion a certain level of cancerogenic attack (by any
cancerogenic agent, radiation being one of them) produces a evolutionary
pressure towards the development of a way to repair the damages or delay
the consequences until post reproduction age. (So the pressure is bigger
for long-lived species.) OTOH cancerogenic agents generally tend to be
mutagenic, too, and thus provide the variations evolution is based on. A
subsequent reduction in exposure level reduces the pressure but produces
no significant pressure in the opposite direction (towards cancelling
these properties). Along with this, the mutation rate declines, too,
conserving the 'status quo'. Both effects should work in that direction
that the development of protective mechanisms follows an increase in
exposure faster than the loss of this properties follows a decrease. So
I expect that the response of a species to a cancerogenic environment is
adequate rather to the high levels of exposure it experienced during its
evolution than to the low levels. 

As for Brian's argument (Why isn't a high protection level forwarded to
later derived species?), I have no real answer, just a thought maybe
someone else can verify or falsify. If the later derived higher
organized species needs a better protection mechanism for establishing
an adequate level of protection, a constant exposure level will produce
evolutionary pressure to develop such an improvement. Under a lower
exposure level the old mechanisms may offer enough protection,
improvement being needless.

Greetings and best wishes for the rest of x-mas and a good y2k,

Harald

Disclaimers as usual.
--
Harald Weiss
weiss@ki.comcity.de (Thanks for the hint, Melissa)
Preetzer Strasse 263
D-24147 Kiel (Germany)
..

************************************************************************
The RADSAFE Frequently Asked Questions list, archives and subscription
information can be accessed at http://www.ehs.uiuc.edu/~rad/radsafe.html