Path: utzoo!attcan!uunet!lll-winken!lll-lcc!ames!ncar!boulder!sunybcs!rutgers!iuvax!silver!chiaravi
From: chiaravi@silver.bacs.indiana.edu (Lucius Chiaraviglio)
Newsgroups: sci.bio,sci.med
Subject: Re: Mortality
Summary: sorry, but not much is known
Keywords: necrology?
Message-ID: <1894@silver.bacs.indiana.edu>
Date: 12 Jun 88 00:09:04 GMT
References: <36@feedme.UUCP>
Reply-To: chiaravi@silver.UUCP (Lucius Chiaraviglio)
Organization: Department of Molecular, Cellular, and Developmental Biology at Indiana University, Bloomington
Lines: 72
Xref: utzoo sci.bio:1231 sci.med:5729

In article <36@feedme.UUCP> doug@feedme.UUCP (Doug Salot) writes:
>In pondering good topics of conversation for dinner parties, I
>suddenly realized that I don't know what that branch of science
>is called in which aging and death are studied (I don't believe
>gerontology is considered a research discipline).

	Actually, I was under the impression that gerontology is supposed to
be considered a research discipline, but not many people seem to be doing
extensive (or any) work on it.

>                                                   Could someone
>enlighten me?  (I'm sure many of you could, but I mean specifically
>about the study of death.)

	I don't know about this one, but maybe thanatology would be the
appropriate term?

>Before I run out and subscribe to Death Today or Popular Dying,
>does anyone want to give a rundown of current theory on the
>subject?  What cellular organelles are depletable (assuming
>suitable nutrients are available from the environment)?  Have
>the mechanisms which determine whether (or how) a cell becomes
>specialized and stops dividing been elucidated?

	No, these mechanisms have not been determined, although it is definite
that aging occurs at the cellular level.  Many people have thought that aging
is the result of accumulated DNA damage, but this theory absolutely fails to
explain how accumulation of DNA damage can lead to aging of individuals yet
allow them to give rise to perfectly young offspring.  A modification of this
theory which has some experimental evidence for it (proposed by Robin
Holliday) states that aging is the result of loss of epigenetic information
about cell differentiation which is stored as methylation of cytosines in
cytosine-guanosine sequences in the DNA -- this information is reset to zero
in the germ line (which is "undifferentiated," or more properly at the
ground differentiated state).  Holliday believes that recombination in meiosis
is responsible for this; could be, but I don't see why recombination should be
required for this.  At any rate, when the epigenetic information about
differentiation is reset, damage to the epigenetic information would also be
reset.

	I propose that the reason for aging (whatever the specific mechanisms)
is that even in the absence of aging the ranks of any generation of most
organisms are quickly reduced (by predation, starvation, disease, accidents,
etc.) to numbers too small for selective pressures that affect them alone to
have a significant effect on the evolution of species as a whole.  Therefore,
mutations whose deleterious effect is considerably delayed (Huntington's
disease is a clinically-characterized example) will incur so little selective
disadvantage that they will appear in the population faster than they are
removed by negative selection.  (Eventually, this will reach an equilibrium so
that they are removed as fast as they appear.)  Taken together, the effects of
these delayed-effect deleterious mutations constitute aging.

>Oh, and while I'm at it, what is the standard definition of human
>death these days?  Is it flatline for some time span?  If so, what
>area of the brain is being monitored?  Are there estimates for the
>amount of cellular damage as function of CNS (or CV) inactivity time?

	I'm not sure if the legal definition of human death has been entirely
settled, although the trend has been to define it as corresponding to brain
death.  I'm not sure how long the EEG has to read flat for a patient to be
pronounced legally dead, but a few minutes without oxygen destroys all but the
most rudimentary functions of the human central nervous system; also, at least
most types of neurons seem to die off if they are not stimulated sufficiently,
but I don't know what the time frame is for this.

	-- Lucius Chiaraviglio
	   chiaravi@silver.bacs.indiana.edu
	   lucius@tardis.harvard.edu	(in case the first one doesn't work)
	"NO DYING ALLOWED." -- The Maytag coin-operated washing machine
		instruction poster.
	"This would be nice!" -- graffitti seen on the Maytag coin-operated
		washing machine instruction poster in the Daniels laundry
		room in Currier House at Harvard University.