Must an AGING PROCESS be universal?

[W.G.VAN.DOORN at ATO.AGRO.NL]

The discussion about the definition of aging between Patrick O'Neil, Oliver 
Bogler and Andy Groves prompted me to give a short thought. I wonder
whether immortal cells have been observed. Of course, there are cell lines
that keep on multiplying, hence can be considered, for all practical
purposes, to be immortal. But have the individual cells in these lines 
been followed? Did they go on dividing since the beginning or did they 
die after a number of replications? In bacterial colonies growing on agar
there are a high number of dead cells within a few days of growth. The
colony keeps growing, but the growth is due to young cells. Immortal cell
lines, therefore, should be compared to species: they will go on multiplying
until extinction.
     
There are plants (ferns and trees) that live for thousands of years. In
such plants, however, each dividing cell has a life which is probably 
much shorter, similar to the situation in the bacterial colony.
          
     Wouter van Doorn
     ATO-DLO, Wageningen, Holland