You bring up a valid point. Doctors do tend to implant multiple embryos (increasing the chance of success) and then often abort the "extras" to either prevent a risky multiple pregnancy or to select the number of children- much as a gardner might thin radishes or carrots. Not a morally good thing to do, if one believes the soul joins the body at conception.
But how do we know that God doesn't give each embryo only the seed of a soul? Just as a fertilized egg is only the potential for a child, perhaps it only has the potential for a soul as well.
Does the unfertilized egg my wife "loses" every month have half a soul? What about the millions of sperm that don't quite make it to the egg? Do they have half-souls?
I don't have the answers- I'm not a priest, philosopher or mystic.
And as I think about it, if a naturally fertilized egg (embryo) naturally fails to implant, the baby is lost also. So should couples not try?
And what if a woman has had a natural miscarriage or two? Should they stop trying because of all the lost children?
There is a solution to the problem of the "left over" embryos after a woman has been successfully impregnated- donate them. There are quite a number of infertile women who would love to carry and give birth to a child.
I appreciate the sincerity of this question, and I'll try to answer it as clearly as I can.
The "soul" means the principle of being a unified, living organism. Plants and animals have souls of a sort inasmuch as they are alive (vegetative and animative souls); but human beings have souls of a higher order, souls which are spirit, because we have capacities which go beyond the physical.
In any case, the identifying characteristic is life: if a given plant, animal or human, at any age or stage, is alive, a soul is by definition present; if it is dead, then a soul is not present.
The Bible sometimes uses the word "life" as a synonym for soul, and sometimes uses the word "self."
It is incorrect to say that a fertilized egg is only the potential for a child. Actually, every child was a fertilized egg at his or her earlist stage. You were once a fertilized egg; and whose child were you then? Your parents', of course. You were at day one of your life, and so you were at day one of being a child--- not a potential child, but a child WITH POTENTIAL!
A sperm, a speck of skin or a bit of brain may be both human and alive, but it is not a "person" because it is not a unified living organism, and so it does not possess a soul. The earliest embryo of only one cell has the capacity, under the normal circumstances, to develop its own cells, tissues, organs, and systems as an integrated living whole; that's why we know that an embrypo is ensouled and a sperm or a skin cell is not.
You asked, "Does the unfertilized egg my wife "loses" every month have half a soul?"
No.
"What about the millions of sperm that don't quite make it to the egg? Do they have half-souls? "
No. They lack the capacity to develop their own cells, tissues, and organs as a unified organism.
"If a naturally fertilized egg (embryo) naturally fails to implant, the baby is lost also. So should couples not try? And what if a woman has had a natural miscarriage or two? Should they stop trying because of all the lost children? "
Well, everybody dies. These naturally occurring deaths are sometimes unnoticed and unmourned (when they are very early) and sometimes very much mourned (I grieved terribly over my two miscarriages) but still they are human deaths like any other. The universal fact that all of us die after some period of life, long or short, does not mean that life is not worth living.
The meaning of anybody's life--- the miscarried child, the newborn who lives but a few days, the man who lives to be 90 --- is a mystery wrapped up in God. We shall know in eternity what was valuable and what was not valuable in our lives of 60, 70, or 80 years!
You wrote: "There is a solution to the problem of the "left over" embryos after a woman has been successfully impregnated- donate them. There are quite a number of infertile women who would love to carry and give birth to a child."
A hopeful thought: but the majority of the parents who "own" these embyronic children don't want them to be adopted by others. They'd rather see them dead. And that's the cold, brutal truth.
Excellent point. Some people are misinformed about IVF and how it works. It is absolutely untrue that embryos (babies!) are killed to make one baby. IVF can be done 100% with respect for every embryo. If 20 embryos are created, the couple can put 2 or 3 back in, and freeze the others. The frozen ones can be put back for another try or donated to a loving couple just dying to have a baby. There are so many on waiting lists right now.
The truth is that we are fearfully made. It takes a LOT to make a human. G-d doesn't just let every sperm meet any egg and poof. 70-80% of the time when a sperm meets an egg, that embryo does not make it.
If a young, fertile, married couple is having regular relations (and always during her fertile time), it could easily take a year to conceive. However, sperm was meeting egg those other cycles (10-14 times in each year). What happens is that even in young women, a great percentage of her eggs are aneuploid (chromosomes not normal or normal in number). These eggs sometimes do result in a conception. Very few might result in a child with a genetic disorder, but most aneuploid eggs and embryos cannot keep dividing to become a baby. They really do stay embryos and have no chance at sticking around.
It is very important to understand that, whatever you feel personally about IVF. If embryos dying naturally is abhorrent to you, then no fertile people should have marital relations. It happens nearly every month. That is why doctors put back 2 or 3 embryos. IVF is costly. They know that most embryos don't have what it takes, regardless of how sperm met egg. They want the desperate couple to achieve a pregnancy. And the success rate of IVF is around 30%. That's about the chances a young fertile couple have of conceiving and staying pregnant, in any given month.