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From: cphoenix@csli.Stanford.EDU (Chris Phoenix)
Newsgroups: sci.bio
Subject: Re: non-genetic evolution... not
Message-ID: <18844@csli.Stanford.EDU>
Date: 24 Apr 91 18:52:12 GMT
References: <79788@bu.edu.bu.edu> <47570@ut-emx.uucp> <79798@bu.edu.bu.edu>
Organization: Center for the Study of Language and Information, Stanford U.
Lines: 80

In article <79798@bu.edu.bu.edu> colby@bu-bio.UUCP (Chris Colby) writes:
>	You are confusing the process of evolution with simple
>change. If the gene pool of the wasps did not change (ie there
>are still the same frequency of male and female determining 
>genes), then the population did not evolve. This is true even
>if there are more females than males compared to some time in
>the past. 

This is getting away from my question, but what do you consider the
gene pool?  If the bacteria mutated and this caused some change in the
wasp, would you say the wasp had mutated?  If you say "no", I have
another question: would you say that we mutate if our mitochondria
mutate?  But the last theory I heard was that mitochondria used to be
bacteria that our cells took in, once upon a time.  (Bill, I wrote
this just before I got your mail.  I'll let it stand as a question to
others, if they're interested.)

Let me give an example to illustrate my point.
>	Humans have been growing larger and heavier in recent
>historical times. But this is not an evolutionary change; it
>is a result of better nutrition and medicine.

This is an extracellular change.  Obviously it is not a characteristic
of the individual cells (ie if you pulled a cell out of Plato and a
cell out of me and grew them in vitro you probably couldn't tell the
difference in their offspring.)  I am not interested in this kind of
change.  On the other hand, Discover did an article about the effects
of malnutrition in the womb, in wartime Poland I believe.  If the
first generation went hungry while the second generation was a
few-month-old fetus, then effects would be seen in the second *and*
third generation, even though the third had normal nutrition.

But I am interested in *intracellular* changes which do not involve
the cell's nucleic acid, and preferably do not involve any nucleic
acid.  Let me give you a hypothetical example that typefies what I am
looking for: Suppose a cell has a structure of tubules.  These tubules
serve as conveyors for various molecules, including some molecule
necessary to build the tubules.  So when the cell divides, the tubules
grow and then the structure splits.  If the structure were removed, it
would no longer be able to grow (and thus couldn't start growing)
since it was necessary for its own growth.  Assuming the cell was
still viable, its offspring would not have that structure.  (I've left
a lot of loose ends in this example, but I hope you see what I mean.)

>Populations phenotypes (expression of genes) can change
>without the gene pool changing. This can often be very interesting
>(as in the wasp case), but it is not evolution.

Should you distinguish between characteristics caused by expression of
the genes and characteristics caused by the environment?  Your human
size example is entirely dependent on the environment.  On a cellular
level, changes caused by hormones are part of the environment and not
part of the cell.  But if you take a cell and its descendent, wash
them carefully, and put them in petri dishes, and the offspring look
different, that is not caused by the environment but by a
transmissible change *inside the cell*.  If that change does not
involve nucleic acid, that is what I'm interested in.

Speaking of hormones, I've been following the discussion on hormonal
control of fetal growth with interest.  But I haven't seen anyone
address the question of where the hormones come from.  I think all of
them will be coded for by the DNA of the original fertilized egg.
Assume that if you take one dinosaur cell, and one chicken cell with
dinosaur DNA, and grow them in a dish, there is no difference in their
phenotype.  So a fertilized chicken-egg cell with dinosaur DNA will
begin by producing dinosaur hormones.  If these hormones spread
through the growing embryo in the same way (which is purely based on
the embryo's environment and physical structure) then the cells will
react to them just like dinosaur cells would.  So the embryo will keep
developing like a dinosaur, and will become a dinosaur.

Notice we've made several assumptions here.  1) The hybrid cells react
exactly like dinosaur cells to all stimuli.  2) The embryo starts the
same physically as a dinosaur embryo (eg. the original egg cell is the
same size).  3) The environment is the same (eg. the pH of dinosaur
yolk is the same as the pH of chicken yolk).  I am interested in case
1), in whether a two cells with the same DNA will have the same
phenotype--ie reaction to stimuli, internal structure, etc.

I hope this is still interesting for people...