Different cells, Different mechanisms

Oliver Bogler obogler at ucsd.edu
Fri Aug 2 19:12:23 EST 1996

EdKrug at aol.com wrote:
> There seems to be a tacit assumption in the Aging research field that one
> mechanism or one small constellation of mechanisms must account for decline
> in function in all cells in all systems of any organism, the culminating
> effect of which is organism death.  I contend that looking at aging from the
> perspective of "Evolution of Longeviety"  offers some important insights into
> the task of increasing healthy lifespan.
> (more that was cut)

Dear Ed,
I found your post interesting and that it makes an excellent point: it is veyy 
common in biology to extrapolate from one system to others, and to assume that 
mechanisms apply very generally. Your point that different cells age in different 
ways is dead on, in my opinion. Clearly, some cells, such as the uninterrupted germ 
cell line never age.

I'd like to add my thoughts on your evolutionary argument:

1) I don't believe that there is *any* evolutionary pressure to extend life. Most 
populations of animals in the wild never reach their maximum age limit, which can 
be seen in captivity. This is because of predation and disease, as well as 
fluctuations in food supply etc. Evolution can't act on something that has no 
selective impact. Humans are no different - the recent leap in life-expectancy is 
due to removal of environmental life limiting influences.

2) In any case, I would turn the whole thing upside down, and say that ageing is an 
acquired strategy in terms of the evolution of life, and is beneficial to a 
sexually evloving species. The reason I say it is acquired is that primitive 
organisms, such as bacteria, do not age - they just divide again and again in an 
unending generational chain (under ideal circumstances - of course they can succumb 
to environmental damage). It is only eukaryotic cells that begin to show ageing, 
and even there some show much less than others. Of course, when you consider the 
germ line as a lineage of cells that exists in many different individuals you can 
see that it doesn't age either - the DNA in you is a copy from the first human, 
which has not been degraded by cosmic rays, or radicals etc. over the last few 
hundred thousand years. Why? Because when nature wants to stop/prevent ageing 
processes it can. It just wouldn't be good for evolution ie. species that don't age 
and turn over their generations quickly enough are not competitive in the big game 
of natural selection.

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