why do we die?

Keith Robison robison at mito.harvard.edu
Fri Oct 27 13:08:31 EST 1995

Erich Schwarz (schwarze.ccomail at starbase1.caltech.edu) wrote:
: TJD. Prior wrote:

: > As a physics student I was thinking and the question came to me Why do we
: > die, Why cant we just regenerate our selves forever. As nobody could give
: > me a satisfactory answer am asking you. If you could answer this simple!!
: > question in basic terms I would I would be most greatfull.

:     A *lot* of people would be grateful, not just you.   >:^)

:     Nobody knows, but, in the case of humans, it looks as if there
: are multiple things that go wrong: gradual cumulative damage to
: DNA, shutting down of cellular replication clocks, and death of
: irreplaceable neurons are the three problems that come most 
: obviously to mind.

:     Another thing that looks pretty clear is that we're not really
: designed to live a long time because, historically, most of us
: were dead at age 35 until very recent (Neolithic) times.  Ergo,
: there's been no evolutionary pressure for genes that make us live
: 1000 years, while at the same time there is probably some short-
: term advantage to having a body that isn't too solidly built.

Richard Dawkins has an article in the current Scientific American
which takes this sort of argument one step further -- that it is
selection hasn't been acting for the longevity of _any_ component,
and therefore they should _all_ be weak links.  

There is an anecdote in the article about Henry Ford.  
He supposedly sent engineers to junkyards to find out what parts 
of his cars had failed.  The engineers reported that they had found 
an example of every piece failing except one -- and so Ford ordered that 
one piece redesigned!

(a sort of counter-view of this general principle can be found in
 Henry Petroski's _To Engineer is Human_, an excellent book)

Dawkins argues that mutation & selection have the same effect on 
living systems.  If there is one component which is much stronger
than needed (compared to the other components in the same system),
then mutation will erode that excess strength.  Hence, getting humans
to live significantly longer might take _lots_ of changes.

Keith Robison
Harvard University
Department of Cellular and Developmental Biology
Department of Genetics / HHMI

robison at mito.harvard.edu 

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