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From: mwd@cray.com (Mark Dalton)
Subject: Re: Reason for Short Life Spans?
Message-ID: <1994Dec28.123002.18094@walter.cray.com>
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Date: 28 Dec 94 12:30:02 CST


Here are a few thoughts.
	These are LARGE systems, one factor may influence all of the others
heavily.  A change in UV radiation/temperature may change the vegitation,
other species, preditors,O2 level, humidity, etc. etc.  This is not meant
to answer, just some ideas.

    Of a single organism:
	1. Changes in:
		- diet (changes because of any of the following).
			- Does it get all of the nutrients it needs.
		- enviroment (UV radiation, temperature, humidity, O2 level).
		- preditors
		- lack of food
	2. Gene pool, if the gene pool shrinks, the likelihood of a 'weakness'
	   is likely to show up.  (Recessive traits, or loss of a gene or a
	   addition of a gene through future generations).
	3. Stress or lethargy - The balance of the system.
	   Metabolism rate *MAY* have something to do with this or perhaps
	   hormone levels.  (The idea is that it may 'wear out' the system
	   like if you drive a car at high RPM's to long OR if you drive a
	   car at to low of RPM's it is always pushing).

    Difference Between Organisms:
	1. Stress to lethargy - It seems (without knowledge of the actual rates
	   of metabolism), that the organisms with lower metabolisms live
	   longer.  The hummingbird - I remember has a Very short life span,
	   The Whale and elephant have longer.   Also most fish have a long
	   life span (I was told that there is no known life span of a fish
	   meaning no age limit - to the ones in nature at least, by natural
	   causes - just preditors, ecosystem changes).
		- I am sure there are MANY exceptions, but perhaps there
		  is some pattern.
	2. There may also be a correlation with the gestation period?
		Or the period of time which a individual can/does reproduce
		before the next generation does.
	3. Changes in: ecosystem, preditors, enviroment (temp,light,UV).
	4. Ability to survive in changes:
		- Preditors, ecosystem changes, temperature, food source.
	5. Size of gene pool.  (inbreeding is not good).
		- Susceptability to disease/virus, ability to fight diseases.
	6. Food availability ( steady source, competition, balanced diet).
	7. The ability of the 'preditor' to change (or organism to change with):
		- New hunting techniques/learning patterns.
		- Virus or disease change to avoid organisms defense.

Via Genetics and cell biology:
	1. Gene pool.
	2. Mutation rate due to:
		a. UV light and other mutagens (chemicals,etc).
			- either the change or protection from the elements
			  (inner layers reproduce, outter coat protects,etc).
		b. DNA Error correction mechanisms.
		c. For multicellular organisms - cell replacement rate.
	3. Cell division limit and life span:
		a. Cells, I think, have a limited number of divisions.
			- I have not kept up in this area.
		b. Cells can have a limited life span.
		c. Ability of cells to dispose of harmful chemicals.
	4. Water and food supply.
	5. Disease exposure - and ability of disease/viral mutation.

Thanks!

Mark
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Mark Dalton       CH3-S-CH2 H H                    H      O       H
Cray Research,Inc.      |   | |                    |       \      |
Los Alamos,NM 87544     CH2-C-COO    //\ ---C--CH2-C-COO    C-CH2-C-COO
mwd@cray.com                | |     |  ||   ||     |       //     |
                            H NH2    \\/ \ / CH    NH3    O       NH3
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URL = http://lenti.med.umn.edu/~mwd/mwd.html

