> Take a look at this paragraph "Many researchers believe that cancer
> occurs in part when apoptosis fails and damaged cells do not
> self-destruct but become essentially immortal."
> Mortality is biologically necessairy as long as already existing cells
> cannot mutate in a way which will be marked on their genes. Since
> mutation occur only on replication, the only way to evolve is by
> replication.
I am feeling picky tonight so let me start by interjecting here. Mutations
can occur at any time. They can only be propagated upon replication.
Therefore mutations which increase the ability of a cell to replicate are
selected for by evolution (ie. survival of the fittest). Cells with
certain specific mutations (eg. p53 knockouts) are better able to
replicate becasue they have escaped one of the failsafe systems designed
to keep them in check (apoptosis) and thus can develop further mutations
which enable them to proliferate. The main theme here is that evolutionary
pressures are working at several different levels. At the organism level
the proliferation of cells is to be kept in check for optimal functioning.
However, the evolutionary pressures at the cellular level operate in
opposition to the organismal pressures. The cells that proliferate "win"
in evolutionary terms. Mortality is not biologically necessary but
controlled proliferation is necessary.
> Immortal cells use the resources needed for the survival of
> their off-springs, thereby killing them.
No, this is not the case. An immortal cell is a cell that is able to
proliferate without limit. It is quite possible and in many cases likely
that an immortal cell will give rise to a cell that is more "fit" in an
evolutionary sense and will outgrow its parent cell and all the other
offspring of the parent cell and limiting THEIR resources.
> Therefore are all mortal by
> heredity. I suppose that the actual mutation which caused mortalness
> first survived when somekind of a disaster or a temporary major change
> in conditions caused a massive death among the mortal cells.
I am assuming that where you wrote mortalness you actually meant
immortalization. It does not seem to make sense otherwise. Cancer which is
a disease of unchecked cell prolferation and immortal cells can be caused
by exposure to harsh conditions (eg a smoker's lung)
> This is the
> only opportunity for their off-springs to survive. Of course there's no
> way to know how much mortalness mutations evolved and perished before
> that certain disaster.
> As usual I'll relate it to memetics - are there any memes which don't
> change at all? don't have any variation or anything; or do they all die?
As in biological systems you could probably find memes that do not change
because they are not being subjected to selective pressures. The more
interesting ones would probably be those that did NOT change in response
to selective pressures.
Duane Hewitt
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http://www.lucifer.com/~duane/aging.html
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