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.
--Brian
------------------------
Brian T. Greuel, Ph.D.
Dept. of Biology
John Brown University
Box 3119
2000 W. University Street
Siloam Springs, AR 72761
(501) 542-7433
(501) 542-9548
EMAIL: bgreuel@acc.jbu.edu OR bgreuel@bstream.com