Re: changing rad levels over time (2)

["Harald Weiß, D-24147 Kiel" <weiss@ki.comcity.de>]

Andrew Karam wrote:

> The latest UNSCEAR report (1996) gives some information on radiation
> resistance of a variety of organisms.  One table in particular (I
> can't
> remember the number, and my copy of the report is at work) shows
> graphically the ranges of LD50 doses for differing classes of
> organisms.
> With the exception of molluscs (which may be explained by the
> shielding
> provided by their shells), these doses change according to the time at
>
> which the types of organisms first appeared on earth.  I can only
> speculate
> as to the reason for this because my academic background is in
> geology, not
> biology, but my co-author is a paleontologist and is starting to look
> into
> that a little more.  It is also intriguing to note that some of the
> more
> slowly-evoloving species (such as the horseshoe crab) have low
> potassium
> concentrations.  This is something else we have not had the time to
> look
> into, but hope to in the future.  Unfortunately, we have no way of
> knowing
> if ancient horseshoe crabs had similar K contents, so we can only
> speculate
> about this, too.  Sigh....

Dear Mr. Karam,

I agree with Mr. Frame, that using LD50 as a measure may be misleading,
but for another reason. LD50 may be of literally vital importance for an
individual, but only in extreme situations, which hardly ever occur. For
the welfare of a species the loss of one or a few individuals is
meaningless. More important for the adaption of a species to a mutagenic
and cancerogenic environment is the balance of harmful and beneficial
effects to least net damage at normal doses. While in cell damage and
cancer their harmful nature is as obvious as the beneficial effect of
hormesis, mutations seem bivalent to me. I suppose most mutations to be
harmful to the individual involved, and as any individual gives its
little share to the faith of its species, a population may be weakened
by a high rate of mutations. But at low rates mutagenese provides the
stuff, evolution is made from (See the horseshoe crab winking?).

I hope you don´t find these thoughts of a layman in this topic tiring.

Greetings, Harald


Standard disclaimer: The opinions I express here are mine, which only
means they don´t necessarily coincide with those of my employer or his
customers.                 B-{)
--
Harald Weiss                 weiss@ki.comcity.de
Preetzer Strasse 263         Tel  +49 431 7859659
D-24147 Kiel                Fax  +49 431 7859658
..