The Washington Post is running a blog on the issue of whether contraception is essentially abortion. This question isn’t new. The issue is related to the issue of when does a human being become a human being, which for the religiously inclined becomes: when does the individual human soul come into existence.
In his writings, the revered theologian Thomas Aquinas was quite explicit that the complete soul was not infused at the point of fertilization but developed along with the ovum, becoming a complete only in the later stages of pregnancy. If you don't believe me, check out the Catholic Encyclopedia:
“St. Thomas's doctrine is briefly as follows:
"…[T]he rational soul is produced by special creation at the moment when the organism is sufficiently developed to receive it. In the first stage of embryonic development, the vital principle has merely vegetative powers; then a sensitive soul comes into being, educed from the evolving potencies of the organism -- later yet, this is replaced by the perfect rational soul, which is essentially immaterial and so postulates a special creative act. Many modern theologians have abandoned this last point of St. Thomas's teaching, and maintain that a fully rational soul is infused into the embryo at the first moment of its existence.”
Catholic Encyclopedia. http://www.newadvent.org/cathen/14153a.htm
What is remarkable about the synopsis of St. Thomas's teachings is how, it was in fact, a depiction of evolution written long before Darwin and his spiritual heir, Pierre Teilhard de Chardin.
Yes Virginia, the soul evolves in the embryo and it evolved in the evolution of the humanity, as everything evolved, from the first moment of the "Big Bang." But the "soul" at the time of fetilization is not a human soul but a vegative soul. Careful eating those carrots.
This is not a rejection of the concept of God, the soul or immortality. It is indeed, a recognition of the grandeur, and as of yet inexplicable, majesty of existence and its Creator. "In the beginning there was the light..."
Opposition to abortion theologically is based not so much on the killing of an innocent life before there is a human soul, but on the interference with the natural law - beginning with self-abuse and continuing through birth control and on to abortion.
But in the body politic as a whole, the natural law argument doesn't really fly. It's much easier to scream murderer. It’s just not theologically - or humanly - correct.