The Christian argument against abortion is based on such an ignorant understanding of human biology. For instance, when does ensoulment happen? If you think, "At conception." is a quick and easy answer, it really isn't given what Steve Pinker says in "The Blank Slate:"
A. There is no moment of conception.
"[R]esearch on human reproduction shows that the 'moment of conception' is not a moment at all. Sometimes several sperm penetrate the outer membrane of the egg, and it takes time for the egg to eject the extra chromosomes. What and where is the soul during this interval?"
B. What about twins?
"[A]s the embryo's cell being to divide, they can split into several embryos, which develop into identical twins, triplets, and so on. Do identical twins share a soul? . . . . Indeed, every cell in the growing embryo is capable, with the right manipulations, of becoming a new embryo that can grow into a child. Does a multicell embryo consist of one soul per cell, and if so, where do the other souls go when the cells lose that ability?"
C. What about chimeras?
"Occasionally two fertilized eggs, which ordinarily would go on to become fraternal twins, merge into a single embryo that develops into a person who is a genetic chimera; some of her cells have one genome, others have another genome. Does her body house two souls?"