One of the most politically significant Evangelical beliefs in modern America is that life begins at conception, and therefore abortion and creating embryonic stem cells for research are forms of murder. Whether or not this is biblical is a question with which I will not be concerning myself.
In particular, I will be making the case that for at least several days, the embryos have no soul (assuming there is such a thing). This will not directly lead to any conclusion about abortion, but it will lead to very definite conclusions about stem cell research and contraceptives that work after conception.
For the first several days after conception, the embryo is a growing mass of stem cells. Nature performs for us the otherwise morally questionable experiments needed to establish its non-humanity.
First, identical twins provide a challenge for the Evangelical view. For the first several days at least, the mass of stem cells can split in two and eventually result in two identical twins. Spiritually speaking, what just happened? Did God create two souls at conception that both inhabited the same cell and later split apart? Did God create one soul to begin with, and then a second soul due to the geographic change of half the mass splitting off from the other half? Pro-lifers rightly argue that if a seven-month old fetus was outside the womb it would be a constitutionally protected person. In other word, God clearly doesn't just create a soul for a baby due to geographic changes. It is equally ridiculous to believe God creates a soul when half of the cells change their geographic location.
But the much more severe problem is human chimeras. Not only can a mass of stem cell split apart, two different masses can fuse. This can result in an apparently normal individual, known as a chimera. Some things about chimeras are a bit odd, like different body parts having DNA that doesn't match, or a mix of different blood types. But someone could be a chimera and not know it. If a soul is created at conception, and two different embryos merge, what happened to the extra soul?
This is a continuum v. discrete problem. The question “is it human?” is yes or no. But the change from sub-human sperm/egg to a fully human baby is gradual. No matter where you choose to draw the line, looking very closely at the line will leave one wondering why the line is here and not there. Even if you say life begins at conception, this problem is only swept under the rug through not thinking about it. Suppose you take a microscope and record the process of conception, and then look at a series of photographs separated by nanoseconds. Can you look at one and honestly say “it's not human here, but in the next one, you can see that God has created its soul?” Even if you could, then take 100 pictures between these two frames and try again. I'm not just being difficult – the way this question is answered determines which forms of birth control are acceptable and which forms are murder. To use a tired analogy, it's like lining up a million shades of gray spanning the spectrum between white and black, and being forced to put them in two categories. Drawing the line is above all of our pay grades.
Ironically, one objection many Christians have to evolution is the way it blurs the line between man and beast. This difficulty is far less severe than reconciling a concept of the soul with embryonic development.
The only reconciliation I found requires the concession that whatever “in the image of God” or “possessing a soul” means, it's not a property of our physical body. Thus, God draws the line, and perhaps at different places for different people. But this accidentally surrenders every single pro-life argument I have heard and more. If “human” is something we cannot determine through physical properties, then why argue “medical fact: life begins at conception?” Why argue that abortion stops a beating heart? Why insist that American Indians have souls based on the fact that they no different? Playing the we-can't-know card in one place is a slippery slope to playing it in other places – quoting Acts 17:26 merely begs the question who is part of a “nation.” The fact is, every position is standing on a slippery slope to horrible atrocities – the safer positions are the ones that realize this and hence step carefully.
This posed an even greater challenge for my faith when I stepped back and looked at what was going on. I was scrounging for the slightest possibility that both reality and my beliefs were true and upon finding one, I was clinging to it for dear life. Nowhere in this line of reasoning had my beliefs been useful for understanding or accurately describing the world, and all throughout they had held me back. I was beginning to believe not because of evidence, not in the absence of evidence, but in the very teeth of evidence to the contrary.
If the way to learn about reality is to look at it, then it's clear that whatever is going on later, there is no soul immediately after conception. In India, sacred cows roam at will while people starve rather than violate the religion over there. In America, medical advancements go undiscovered because experiments with sacred blobs of stem cells violate the religion over here.