Path: utzoo!attcan!uunet!cs.utexas.edu!asuvax!noao!ncar!midway!quads.uchicago.edu!chi9
From: chi9@quads.uchicago.edu (Lucius Chiaraviglio)
Newsgroups: sci.bio
Subject: Re: Ageing
Summary: Causes
Keywords: ageing
Message-ID: <1990Oct28.235942.6175@midway.uchicago.edu>
Date: 28 Oct 90 23:59:42 GMT
References: <1990Oct28.115724.7345@newcastle.ac.uk>
Sender: news@midway.uchicago.edu (News Administrator)
Organization: Department of Biology at University of Chicago
Lines: 41

In article <1990Oct28.115724.7345@newcastle.ac.uk> W.P.Coyne@newcastle.ac.uk
writes:
>What are the current theories on the causes of ageing.
>Here are some I have heard of 
>1. Accumulation of damage to the body.

	This is not the major cause of aging, since even organisms living
under no stress age not much slower than ones living under stress (though the
latter may be killed off much earlier due to their declining ability to cope
with stress).  More important is the fact that the body's ability to repair
damage decreases with age.

>2. Caused by the slow increase or decrease of chemicals in the body.

	The same applies here as to 1.  However, the body has no ability to
remove some chemicals, such as heavy metals, and such things will be a time
bomb.  However, the body usually ages to death long before this occurs.

>3. Gene time bomb - evolution can remove genes which cause early death
>   in a population, because the carriers are less successful reproductively
>   but genes which cause late death are less likely to be removed.  And
>   genes which kill after the animal has ceased being able to reproduce 
>   will not be removed.

	Exactly.  Also, add the fact that genes which give an early advantage
but have later deleterious effects of similar magnitude will be selected for,
because the sub-population upon which they are acting early in life is a
greater fraction of the population.

>4. Accumulated damage to the DNA of the cells causes them to slowly go 
>   wrong.

	No.  If this were a cause of aging, babies would be born old.
Accumulated DNA damage can cause individual cells to go wrong, causing cancer
and an increased incidence of birth defects (when a gamete or one of the few
cells in the early embryo gets hit), but is not responsible for general
cellular aging, except in extreme cases.

|   Lucius Chiaraviglio    |    Internet:  chi9@midway.uchicago.edu
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|   Lucius Chiaraviglio    |    Internet:  chi9@midway.uchicago.edu