From: sfm@manduca.neurobio.arizona.edu (Stephen Matheson)
Newsgroups: talk.abortion,alt.birthright
Subject: Re: When is a fetus not a person?
Date: 26 Jan 93 02:08:53 GMT
Distribution: usa
Organization: University of Arizona UNIX Users Group

From article <C1Fozz.Gzt@news.cso.uiuc.edu>,
by parker@ehsn17.cen.uiuc.edu (Robert S. Parker):

> sfm@manduca.neurobio.arizona.edu (Stephen Matheson) writes:

>>From article <1993Jan19.004526.25747@Princeton.EDU>,
>>by datepper@phoenix.Princeton.EDU (David Aaron Tepper):

>>> In article <1993Jan18.230432.20379@organpipe.uug.arizona.edu>,
>>> sfm@manduca.neurobio.arizona.edu (Stephen Matheson) writes:

>>>>From article <1993Jan17.085933.8172@Princeton.EDU>,
>>>>by datepper@phoenix.Princeton.EDU (David Aaron Tepper):

>>>>> I finally found the article I was looking for: _The_New_Republic_,
>>>>> Dec. 7, 1992 issue. There's a story about the use of RU-486 as a
>>>>> "morning-after" pill. It seems that the egg, up until 14 days or so
>>>>> after conception, has nothing that can confer even numerical
>>>>> identity on it. I'm butchering the article badly, of course, but
>>>>> do read the article.

> [discussion of humble admissions and punishments omitted]

>>> Okay, the gist of the article: Let's say there is an egg that splits
>>> into two, forming what will become two identical twins. The question
>>> is, what happened to the original egg?

>>> a) The egg is dead. If this were true, the mother should not only
>>> be rejoicing that she has two healthy children, but mourning the
>>> loss of the original egg. Nonsense.

>>Uh-huh.

> [Is that agreement?  I would *think* so...but he almost sounds sarcastic.]

Heh.  Six keystrokes later (seven if you count the .), I'm sounding
sarcastic.  My agreement with the conclusion that mourning for the
lost egg is nonsense was grunted with some gruffness to indicate my
skepticism that this would lead to anything any less nonsensical.

>>> b) One of the twins is the "real" original egg; the other twin is
>>> only a copy. Yet both twins have an equal claim to be that original
>>> egg. How can one differentiate which one is the original egg? Scrap
>>> this one.

>>Okay.

> Besides, if that were a reasonable way of thinking of it then only one of
> your cells would be the *real* you, and it would probably have died a long
> time ago.  Too bad.   ;)

>>> c) The egg is split up among the two new twins. While true as far as
>>> this goes, this means that at the two-cell stage, half of each twin
>>> is the original egg, and the other half is material gathered from
>>> "outside" the original. Which leads to saying that neither is the
>>> "real" egg.

> Actually, material is not "gathered from outside" the egg until
> implantation, which does not occur until after many many divisions
> (at which point twinning is not possible).  I'm sure you knew that.
> Each one is only *half* the "real" egg.  They are able to develop to
> full size because they can absorb material through the placenta.
> (I don't think non-mammals have twins comming from the
> same egg, which is because they only have the material in the egg
> itself.) If you *meant* gathered from the placenta, well that doesn't
> happen until implantation, and it accounts for essentially all of the
> mass of a newborn. (otherwise, we'd all be the size of a pinpoint)

>>> The article goes on to note that there is nothing in the genome that
>>> codes for identical twinning -- instead, it is caused by environmental
>>> factors, e.g. a temporary cutoff of oxygen. Since twinning can occur
>>> up until about 14 days after conception,

>>Really?!?  I can see a morula, or even a blastula, dividing into 2
>>identical halves, but at 14 days I'm guessing that the embryo is
>>awfully complex...  I'll look this up...

> I would doubt twinning at 14 days.  If someone has a reference that it is
> possible...ok.  I remember learning that cell differentiation is significant
> after 8 divisions (256 cells), which I'm pretty sure happens before
> implantation which is (I hope) sooner than 14 days.  After that point,
> separation would not lead to two well-developed twins.  There may be some
> other mechanism of twinning, but I don't know how it could occur.

See Mark Cochran's followup, where he describes the various twinning
scenarios and their probabilities of occurrence.

>>> until that point there is
>>> no reason to believe that the egg even has "numerical identity". (To
>>> tell the truth, I see where he is going, but it could still be argued
>>> that as long as only one copy of the egg exists, it certainly does
>>> have numerical identity. The logic here, now that I've gone over it,
>>> is admittedly fuzzy.)

> That piece of fuzz under your bed is also "unique".  I guess that would
> make it "bad" to vaccuum it up and destroy it's structure...  Kinda silly,
> huh?   ;)

Huh?  Were we talking about uniqueness?  Are you being silly, Rob, or
did you think there was something silly before your silliness?

>>My problem with all this is that IMO the egg ceased to exist the
>>moment it divided.  In developmental biology, we talk of symmetric
>>and asymmetric cell division.  The cleavages of the egg and of the
>>blastomeres are examples of symmetric division: one cell divides to
>>yield 2 daughters that are roughly equivalent.  In this case, it
>>becomes rather odd to consider the continued existence of the
>>original cell.

> I don't think that's a very good way of looking at it.  All of your cells
> will either die or divide symetrically within the next week.  (maybe less)

*NOT*!!!  Your neurons haven't divided since the day they differentiated
into neurons.  Most of your neurons were born before you were, and, 
outside of the olfactory system, we're pretty sure that none of them
has ever divided.

Many of the cell divisions that will occur in the next week will be
asymmetric, with the original cell continuing to exist for perhaps
years.

> Does that mean that you cease to exist a week from now?  Hopefully not.

Your point is well-taken, even if your premise is wrong.  Human existence
and personhood are (in my definition) properties that transcend the
existence of cells, and certainly don't reside within them.

> A better way to look at it might be that the egg is "developing" (but the
> same egg).  After all, a chicken egg does not become a different egg just
> because the chicken develops from a single cell to a pre-born chick.

But, Rob, if somehow the egg "developed" into 2 eggs (i.e., twinning
occurred), then which egg is "the same egg"?

>>                The repeated divisions of some neuroblasts are
>>examples of asymmetric division: one cell divides to yield a
>>daughter and another neuroblast identical to the first.  In this
>>case, the neuroblast is considered to be repeatedly dividing
>>asymmetrically to yield progeny; it is considered to "survive"
>>the divisions.

> But this doesn't happen early in the development where twinning is possible,
> does it?  (in humans)

I don't know the answer to this, but I can think of no reason that it
should not occur.

>>I don't claim to understand the spiritual implications of twinning,
>>given a definition of personhood or ensoulment beginning at
>>conception.  But I'm also not sure how useful this "numerical
>>identity" stuff can be.

--

Steve Matheson   Program in Neuroscience   University of Arizona
sfm@neurobio.arizona.edu
Newsgroups: talk.abortion