Re: changing rad levels over time (2) -Reply

[FRAMEP@ORAU.GOV]

Andy:

Some quick thoughts/questions:  

The repair mechanisms you  talk about being retained are repair
mechanisms for genetic damage, not radiation induced genetic damage
per se.  There were lots of environmental factors 3 billion years ago, as
well as today, that produce genetic damage. Isn't the bulk of genetic
damage caused by agents other than radiation? How do you propose to
isolate the effect of ionizing radiation?

If other agents than radiation are causing genetic damage, genetic repair
mechanisms would seem to be advantageous - what would be the
evolutionary pressure to eliminate such a mechanism?

How do you know what radiation resistance organisms possessed 3
billion years ago?  That they survived higher radiation levels than we
have today, doesn't mean they were more resistant, in fact they might
have been less resistant than organisms today for all we know.   It
would seem that you are trying to build a scientific case against pure
speculation.

Are you trying to compare the radiation resistance of primitive organisms
with their modern counterparts -  or are you assuming that modern
bacteria (for example) are identical to their primitive counterparts and
comparing them with highly evolved organisms such as mammals? If so
how do we compare radiation resistance in , for example, protozoa and
mammals? Using the LD50 as a measure of radiation damage repair
mechanisms might be a bit misleading.  Isn't the LD50- in mammals due to
damage to the hematopoietic system? A system that you don't have in
bacteria and algae (nor is cancer an issue with bacteria and algae). It
always seemed to me that comparing LD50s between radically different
organisms was like comparing apples to oranges.

Regards

Paul Frame
Professional Training Programs
ORISE
framep@orau.gov