From: knapp@spot.Colorado.EDU (David Knapp)
Subject: Re: Shameless attack on pro-choicers in general!
Organization: University of Colorado, Boulder
Date: Fri, 14 Aug 1992 02:21:24 GMT

In article <1992Aug10.161448.6148@csus.edu> chaneysa@nextnet.csus.edu (Stephen A Chaney) writes:
>
>This is supposed to be a devastating attack? Okay, Mr. Perez, get out
>your pen and paper, class is in session: 
>
>1) Not one single cell in the human body has genetic codes for other
>organs except for that organ which the given cell is a part of.
>Stomach cells only have stomach cells, with no provision for brain
>cells or arm cells.
>The zygote cell does, in fact, have within it, departments WRT
>his/her genes, that handle arm, leg, and stomach growth.  
>FACT: Not one cell in your body differentiates. Only the zygote can do
>that. This fact contradicts your first point. 
>2) Twins: The presence of twins produces the question of whether we
>have one human individual, or two, within the same zygote. DEFINITELY
>NOT ZERO. Triplets means we have three individuals growing out of one
>zygote. Quadruplets? FOUR individuals. All of whom are sitting in that
>one zygote, and growing out. They couldn't grow out unless they were
>there in the first place, at fertilization. 
>This contradicts your second point.  
>

I thought you all might be interested to hear what a biology expert has
to say about Mr. Chaney's biological comments above.


Professor Purves' response to Mr Chaney's claims follows.

> 1) Not one single cell in the human body has genetic codes for other
> organs except for that organ which the given cell is a part of.
> Stomach cells only have stomach cells, with no provision for brain
> cells or arm cells.
> The zygote cell does, in fact, have within it, departments WRT
> his/her genes, that handle arm, leg, and stomach growth.  
> FACT: Not one cell in your body differentiates. Only the zygote can do
> that. This fact contradicts your first point. 

Just about every statement in this paragraph is false.  Especially
the "FACT."

> 2) Twins: The presence of twins produces the question of whether we
> have one human individual, or two, within the same zygote. DEFINITELY
> NOT ZERO. Triplets means we have three individuals growing out of one
> zygote. Quadruplets? FOUR individuals. All of whom are sitting in that
> one zygote, and growing out. They couldn't grow out unless they were
> there in the first place, at fertilization. 
> This contradicts your second point.  

This set of statements is hard to discuss, in that I cannot grasp
the concept of "individuals" "sitting in" a zygote and "growing out."
A person doesn't "grow out" of a zygote; the zygote DEVELOPS INTO a
person.  Biologically speaking, that is...

In the case of identical twins, the zygote (fertilized egg) divides;
the resulting two cells become separated; and each of those cells
DEVELOPS INTO a distinct person.  In a single birth, the products
of the first division of the zygote stay together and develop
(roughly speaking) into two halves of the resulting person.

> 1) "Sperm and ova do this with the right conditions..."
> Interesting that the condition required, is fertilization. Which
> points right back to where life begins... 

I don't find that either participant in this debate is getting
anywhere.  For what it's worth, it is possible in some cases to
raise plants from pollen that hasn't participated in fertilization.
Male ants, bees, and wasps are haploid and thus haven't resulted
from fertilization.  Females (the vast bulk of these hymenopteran
populations) are diploid and result from fertilization.

> 2) A zygote only needs nutrients and a non-hostile environment to 
> grow into a newborn baby. A newborn baby needs nutrients and a
> non-hostile environment to grow into an adult. 
> What is the difference? A zygote is proportionally inferior and far
> more vulnerable than a newborn, but a newborn is proportionally
> inferior and far more vulnerable than an adult. 

A (human) zygote needs lots more than nutrients and a "non-hostile
environment."  While plants can be raised from single cells in vitro,
this cannot be done with a mammalian zygote.  Thus far, we can't
get from zygote to baby without the maternal environment.

> 1) Ova and sperm are potential humans because they do not have the
> power to differentiate, until they fertilize. They aren't even growing
> or developing. The z/e/f does. A common person's view of what I'm
> saying, might be, "Feed all the chicken soup you want, to sperm, ova,
> skin cells, or warts, but they just won't differentiate." Can't say
> that about the z/e/f.

Eggs and sperm do develop, in a biologist's terms.  Otherwise, you
are okay with this statement.

> 2) The question of identical twins can also be approached by asking,
> "Do we have one individual human, or two?" 

Identical twins are obviously two individual humans.

I haven't commented on the other numbered items, because they are
political statements rather than biological ones.


Me (David Knapp) again... 

Below I ask Prof. Purves several pointed questions relating to Mr. Chaney's
assertions. My questions are denoted by >  His responses aren't denoted.


> Some direct questions are:
> 
> Do multiple births come from multiple eggs or from whacky things happening
> at early cell division stages.

Identical twins derive from a single egg.  If the daughter cells
produced by mitosis of a zygote separate, you get identical twins.
Fraternal twins derive from two eggs, fertilized by separate sperm.

> Is the same DNA in all cells?

To a first approximation, YES.  There are exceptions.  For example,
eggs and sperm are haploid and have only half the genetic information
found in somatic (body) cells.  Mammalian red blood cells lack
nuclei at maturity and hence have NO nuclear DNA.  Those white blood
cells that give rise to the immune system splice out part of their
DNA as part of their differentiation to become specific for a
given antibody or T-cell receptor.

However, "stomach" and "brain" cells have the same DNA except for
chance mutations in individual cells that are not related to their
position in the body.

> Does the DNA contain the 'code' for all body parts and functions? Is 
> the DNA in my brain cells different than the DNA in my stomach cells?

Yes (first question).  No (second question).

> When does a fetus get along enough to have brain activity begin? When 
> does myelination occur?

"Brain activity" is not a single, simple thing.  Some parts of the
brain, such as the cerebellum and thalamus (for example) don't
specialize until the middle of the second month.  At about this
time, some reflexes are operative, and the brain may be regulating
some of the organs.  For this to happen, myelination has to have
taken place.

The events just described aren't really fetal events, but early
embryonic.  The term 'fetus' usually applies to an embryo at least
two months along in its development.

> You can see where this is heading, but I need the facts, no hearsay.

My remarks derive from standard books of introductory biology and
developmental biology.  I am not well informed on the last two
questions (concerning neural development), but I looked the material
up in outstanding textbooks.

> Thanks for responding!

You're welcome.

(bill)

Professor Purves' credentials below.

B.S. Caltech 1956, Ph.D. Yale 1959.  Chaired biology departments at
UCSantaBarbara, UConn, and (now) Harvey Mudd.  Current textbook is
Purves, W.K. (Harvey Mudd College), Orians, G.H. (U. Washington),
and Heller, H.C. (Stanford).  LIFE: THE SCIENCE OF BIOLOGY, 3rd
edition.  Sinauer Associates and W. H. Freeman, Inc.  1992.  In
use at over 110* colleges and universities this fall term.  *(Includes
Harvard, Yale, MIT, Stanford, Michigan, Berkeley, UCLA...)

From his assertation of Chaney's claims, and other experts I have talked 
to around the world about Chaney's claims, I, and presumably you, would
have to conlude that Mr. Chaney doesn't show much knowledge of biology.

I would go so far as to say he is ignorant of some fundamental areas of 
biology which are quite important to understand if one is to make claims about
biological relations to abortion.

Chaney should either read up more on biology before making incorrect statements
or stop attempting to discuss human biology and fetal development.   

-- 
David Knapp                                      University of Colorado, Boulder
Highly Opinionated, Aging  and                      knapp@spot.colorado.edu
Perpetual Student of Chemistry and Physics.
            Write me for an argument on your favorite subject.
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