Ageing as an evolutionary force

Michiaki Masuda masuda at
Thu Apr 16 16:34:36 EST 1992

In article <1992Apr14.162049.14039 at> house at (Daniel J Housman) writes:
> [The first paragraph deleted.]
>	Ageing like flowering in angiosperms could be an evolutionary 
>advantage that promotes recombination and thereby promotes diversity 
>that allows survivability. People generally think that aging is a
>process which is necessary and a process that must occur merely because
>the world is too harsh for an organism to survive in it intact defeating 
>entropy for a prolonged period of time. This is not completely 
>sensible. It is possible to produce cell lines of cancer cells that 
>are essentially immortal. The machinery for immortality exists and were it
>to be evolutionarily advantageous to not age and live forever then the
>world would have evolved with organisms that were immortal. 

 Cancer cell lines such as HeLa cells are immortal as a "cell line." It is
least likely that there exist any cells that are immortal as a single cell.
(Well, something like plant seeds and spores can be revived even after
thousands of years, but they may not be worth calling a "living" creature.)
Therefore, it might be necessary to define the "machinery for immortality" in
two ways; the machinery that  guarantees cell devision before cell death, 
and the machinery that keeps individual cells as they are for ever.
 Immortal cell lines are the ones that obtained the first machinery. On the
other hand, when we talk about the immortality of a multicellular organism
we may have to consider the second mechanism, too. 

>	The reasons why the aging process is useful evolutionarily are as
>follows. If there were not a younger generation and an older generation there
>would be intermating between generations causing a lack of recombination
>that would normally be caused by the constant reshuffling of genes from one
>generation to the next.  

 Many species including Homo sapiens are potentially capable of intermating
between generations. I wonder if inter-generational mating has been such a 
strong selective pressure. If it is, some other mechanisms (e.g., genetic
homophobia?) might be more crucial to avoid it.

> [Some staff deleted.]
> There is no great advantage to staying
>alive longer since major injuries occur making the organism less fit such
>as the loss of limbs. 

 We could have been evolved without losing the ability to regenerate that 
some lower forms of life have.

> [Some staff deleted.]
>	What this would mean is that there are some inherent causes of aging 
>that ought to be conserved throughout the cells of all organisms and the 
>DNA must somehow code for this process. This process is probably one of
>the fundamental processes of biology and deserves some attention to its
>biochemistry. The research that would need to be done would be what factors
>be it flaws in the DNA or cellular clocks are causing aging and how can they
>be manipulated.
>Dan Housman
>95 MIT

 I completely agree. Some people (including myself) started to pay attention
to the inherent suicide function that is called programmed cell death
or apoptosiis. This apparently disadvantageous mechanism are supposed to
be essential for some developmental processes, such as morphogenesis and
immunological tolerance. I'm not sure if and how this suicide function could be
linked to aging or senescence, but it might be possible to imagine that 
aging is caused by a chronologically and spatially incorrect expression of
suicide genes. Senescence itself may not be advantageous for prosperity of
species, but the loss of function that could cause senescence might have been
disadvantageous. If that is the case, aging is the price that we are paying
for our fingers, toes, eyeballs, ......? 

Michiaki Masuda
Laboratory of Molecular Oncology
National Cancer Institute
Bldg. 469, Rm. 140
Frederick, MD 21702-1201
Phone: (301) 846-5740
F A X: (301) 846-6164

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