MadSci Network: General Biology

Re: Is there any living being which does not die of 'natural death' ?

Date: Mon Oct 15 15:26:45 2001
Posted By: Aydin Orstan, Staff, Office of Food Additive Safety, Food and Drug Administration
Area of science: General Biology
ID: 999789781.Gb

Dear Hughes,
I don't think that is an answerable question. First of all, how would one 
figure out the "ideal conditions" for an organism that ordinarily has a 
long life span? Ideal conditions mean unnatural conditions. For example, 
animals kept in highly artificial conditions in zoos generally live longer 
than their wild counterparts. Those conditions were determined mostly by 
trial and error and not to extend the animals' life span, but primarily to 
maintain them healthy. To figure out the most suitable artificial 
conditions to extend the lifespan of a tree species that under natural 
conditions lives hundreds of years anyway, one would have to do 
experiments lasting hundreds of years!

Any organism that reproduces asexually (for example, by division or 
budding) may be considered immortal provided that its genome never 
changes. For example, a bacterium divides into two and then those two 
bacteria each divide into two, and so on. So it seems that the original 
bacterium never really dies. Actually, that is not quite true. The 
bacterial genomes tend to change quickly as a result of mutations or 
horizontal gene transfer. So, after a large number of divisions (which 
don't take very long), the descendents of one bacterium may be quite 
different genetically than their common ancestor. Therefore, none of those 
descendents would be the original bacterium anymore. 

Similar processes that raise similar issues take place in many 
multicellular organisms. The cattail plants that commonly grow in ponds 
produce rhizomes, which are roots from which new plants can grow. As a 
result, a cattail plant that has grown from one seed in a newly formed 
pond may eventually end up filling up the pond with cattails connected to 
each other by their roots and that could be considered one giant plant. 
Will that plant still be there if the pond is not disturbed for, say, 1000 
years? We would have to wait 1000 years to answer that question. If the 
plant is still there 1000 years from now, will it genetically be the same 
plant that is in the pond now? We would have to wait 1000 years to answer 
that question too, because there is no way to predict if a population of a 
species or a clone of an asexual organism will undergo genetic changes 
during a 1000-year period.

Aydin Orstan

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