"John W Burgeson used the following statements to argue that "abortion
before
implantation is not proscribed":
1. A zygote may "split" along the way
2. Two zygotes may "fuse" along the way
I'm having trouble following the logic connecting these statements to the
above
argument about abortion. But first of all, let's make sure we can agree
on some
terminology.
Zygote = a fertilized egg. The only splitting it does is to cleave into
a
two-celled embryo. The cells of this two-celled embryo could
potentially
separate from one another to give rise to two separate embryos (identical
twins), but this happens extremely rarely. Most instances of identical
twinning
occur as a result of subdivision of the inner cell mass at the blastocyst
stage
of development.
Similarly, I doubt that fusion of two zygotes (fertilized eggs) occurs
very
often, if at all. The zona pellucida that surrounds the eggs would make
cell
fusion very difficult, if not impossible. It is more likely that fusion
would
occur in early cleavage stage embryos (perhaps those with a damaged zona
pellucida) or after the blastocyst "hatches" from its zona pellucida once
it
reaches the uterus. In any case, fusion of two separate embryos could
give rise
to a single chimeric embryo that actually consists of cells from two
genetically
distinct embryos.
Okay, so these events happen, albeit very rarely. But they happen
spontaneously
without any direct, purposive intervention by anyone, except perhaps God.
How
can you use these spontaneous events to argue in favor of a mechanical or
chemical intervention by human beings that hinders cleavage or prevents
implantation of the blastocyst in the uterus? I'm missing something
here."
OK, I think I see what you are saying. The problem seems to be with the
definition of "zygote." My Webster's unabridged does not help a lot; it
seems to imply the definitions I gave earlier -- that "zygote" refers to
the entity from point C (conception complete) to point D (implantation).
After that it is an embryo.
You are using the term "embryo" to refer to the entity between a point in
time (call it X) when the zygote has completed its first split into a
2-celled being on through implantation.
I am not beholden to my definitional setup -- it is second-hand from an
ethics class two years ago. So confirm my understanding (is my above
discussion correct?) and we can go from there. Here is how I understand
you:
A two entities, a male sperm and a female egg
time passes
B the process of conception begins
time passes (how long is typical? 2 hours?)
C the process of conception is complete
time passes (again, how long?) We call this the zygote
X The zygote completes a division into 2 cells
time passes. (how long?) The entity is called an embryo during this time.
D Implantation occurs
time passes (how long?). The entity is still called an embryo
E The time is now 8 weeks after point C
time passes (56 weeks). The entity is called a fetus during this time.
F Birth occurs.
I'll stop here and see if we are in definitional sync.
Burgy
Burgy
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