Newsgroups: comp.ai.philosophy,talk.religion.newage,alt.atheism,alt.pagan,alt.consciousness
Path: cantaloupe.srv.cs.cmu.edu!das-news2.harvard.edu!news2.near.net!bloom-beacon.mit.edu!news.media.mit.edu!minsky
From: minsky@media.mit.edu (Marvin Minsky)
Subject: Re: THE INCREASING HUMAN LIFE SPAN
Message-ID: <1994Dec24.160827.27957@news.media.mit.edu>
Sender: news@news.media.mit.edu (USENET News System)
Cc: minsky
Organization: MIT Media Laboratory
References: <3dgovo$pp8@tuba.cit.cornell.edu>
Date: Sat, 24 Dec 1994 16:08:27 GMT
Lines: 49

In article <3dgovo$pp8@tuba.cit.cornell.edu> ro11@crux4.cit.cornell.edu (Rohan Oberoi) writes:
>minsky@media.mit.edu (Marvin Minsky) writes:
>>hubey@pegasus.montclair.edu (H. M. Hubey) writes:
>
>>>This probably assumes that the present knowledge about the limit of
>>>cell division [cells seem preprogrammed to split about 50 times
>>>before they self-destruct] will always hold true and that we can
>>>never do anything about it.
>
>>No, I didn't assume that.  The "standard" theory is that the Hayflick
>>limit may have evolved to prevent accumulations of errors that
>>increase the chance of cancer.  I don't know if the evidence for this
>>is any good, though.
>
>First, this isn't my field, so I apologise if this seems off the wall.
>
>I take it the Hayflick limit reduces the chance of cancer, according
>to this theory, by ensuring that the cells in the body at any given time 
>are not all as old as the organism itself, and have not gone through as 
>many divisions (and hence accumulated as many errors) as they would have 
>had they been so.  This implies of itself that a mechanism for replacing
>cells that succumb to the Hayflick limit during the lifetime of the 
>organism is at work, at least until the onset of senescence, and that the
>new cells created by this process produce the suggested evolutionary
>advantage by being younger than the organism itself, and so having 
>fewer errors and being less prone to cancer.


There isn't any single  "onset" of senescence.  There appear to be a
variety of aging processes, including accumulated damage to various
intracellular systems.

As for the Hayflick limit, looks like you might have the wrong sign.
It is thought that cells become cancerous throughout life, but most of
them can't reproduce enough to kill you.  **Malignant cancer is when
the mechanism for the Hayflick limit itself gets damaged.** 

>...  This implies of itself that a mechanism for replacing
>cells that succumb to the Hayflick limit during the lifetime of the 
>organism is at work, at least until onset of senescence, and that the
>new cells created by this process produce the suggested evolutionary
>advantage by being younger than the organism itself (and so having 
>fewer errors and being less prone to cancer).

Many important cells are not replaced at all.  For example, neither muscle or
nerve cells are normally replaced after loss, although there are a few
exceptions.


