How evolution works

Cathy Woodgold woodgold at seismo.emr.ca
Thu Jun 9 09:46:15 EST 1994


Thank you for your apology!  Apology accepted.  I don't have the original
post, either.  The point I was trying to get across I'll make another attempt
at explaining.

I'm imagining an inividual who takes drugs to lengthen the telomeres in the
cells of his/her body so that he/she can live a long time.  My point is that
the individual will inevitably get cancer unless some powerfull way of
controlling it is found.  (Other people on this newsgroup have been making
this same point.)

I'm making an analogy between two lines of human cells.  A "line" of cells
is a set of cells such that at any time there is only one which is considered
an active member of the line, and the cells are all connected through time
with each other via cell reproductive events (mitosis, meiosis and fertilization).
Both lines I'm considering are 1000 years long.  One is a typical normal cell
line existing in a line of humans of normal lifespan.  Let's suppose it starts
with a sperm cell;  then it includes the fertilized egg that that sperm fertilizes;
it includes one, at any given time, of the cells of the developing fetus;
as the fetus develops ovaries or testicles, the cell line I'm interested in
includes one at any time of the cells of those ovaries or testicles
(if it were any other part of the fetus' body it wouldn't be a 100-year-
long cell line, would it?  It would be limited by the individual's lifespan.)
Then after that individual grows up, it includes an egg or sperm which 
is fertilized and becomes another individual, and so on.  Now, it's easy to
choose such a cell line in retrospect.  I can look at my arm under a microscope
and say "I'm talking about this one cell, and it's parent cell before
the last mitosis, and it's parent, and so on...  except that with fertilization
there are two parent cells, so I always choose the egg cell in that case.
So I'm talking about the parent or egg-parent cells, of this particular cell,
going back 1000 years."  It's much harder to predict beforehand which cell
of a small fetus will be the parent of an egg or sperm which will successfully
develop into another human, or which sperm will fertilize an egg and grow,
etc.

The other line of cells I'm talking about is an imaginary line of cells within
 the body of an individual who is living 1000 years because that individual
takes drugs to lengthen telomeres and takes other steps to live a long time.

The point is that the individual is likely to get cancer.  This doesn't mean
one shouldn't try to live longer;  just that one of the major means is
battling cancer.  The reason the individual is likely to get cancer is
as follows.  During the normal 1000-year cell line, a lot of natural selection
takes place.  Seriously defective eggs, sperm and other cells do not form
part of the cell line.  Fetuses who have seriously damaged genes (caused
by poor nutrition, xrays, or other causes) miscarry and don't form part of
the 1000-year cell line. Etc.  The natural selection favours normal human
development.

Within the individual who is living 1000 years, a lot of natural selection
also takes place.  However, most (at least) of this natural selection favours, not
normal human development of the body as a whole, but survival, reproduction
and success of individual cells and groups of cells.  Usually the success of
cells contributes to the success of the individual as a whole, and I suppose
the natural selection of cells within the body is a necessary part of healthy
human development.  But it does tend to lead to cancer, which is simply
some cells becoming extremely effective.

Here's another analogy:  J. Lovelock in The Ages of Gaia talks about life
on earth as one whole organism.  The mechanisms of evolution of Gaia are
somewhat different from the mechanisms of evolution of species, since there
is just one Gaia (no ongoing natural selection of planets).  However, often
the evolution by natural selection of species benefits Gaia as a whole in
ways which are not exactly coincidental.  For example, some organisms exert
a beneficial influence on local climate;  natural selection for these
has us ending up with a lot of species which therefore exert a beneficial
influence on the climate as a whole.  Evolution and natural selection are
very complex things.  I keep learning new things about them.  For example,
it just occurred to me that within our bodies there may be a certain amount
of natural selection of cells which prevents cancer;  for example, if a
precancerous cell tends to suck nutrients away from the cells around it,
perhaps it kills them and perhaps this tends to result in its own death,
or at least the death of some other precancerous cells, which are likely
to be near (because closely related to) the one cell I started talking about.
Anyway, the study of the evolution of Gaia may shed some light on the
long-term survival of individuals, and vice versa.

Cathy       TISSATAAFL 





More information about the Ageing mailing list