Richard Doerflinger was a representative of the U.S. Conference of Catholic Bishops.
His summary below is a easy to read version of the Vatican 1974 encyclical on abortion.

 

The following discussion is taken from the question and answer period following Session 7
of the April 25, 2002, meeting on the ethics of stem cell and cloning research
of the President's Council on Bioethics

  DR. GEORGE: Richard, since you're here, I thought I could get an answer to a question that frequently comes up, and it's this. Does the position of the Catholic Bishops Conference, or the Catholic Church generally, on the issue of the moral status of the embryo and what public policy ought to be on that depend on a view about the infusion of a spiritual soul in the early embryo?

  MR. DOERFLINGER: No. There have been a lot of speculations during the course of Catholic history about ensoulment. Even during times when people thought they were pretty sure based on the biology of Aristotle and the philosophy of Thomas Aquinas that the early embryo was not ensouled, it still rejected abortion as an act that shows disrespect for this developing life that has a human destiny, that God is at the very least forming to prepare for a soul.

  The current teaching is that abortion and destruction of embryos is wrong, first of all, because it destroys a living member of the human species, and that that's enough to deserve our respect.

  And, secondly, that since we cannot be sure that the early embryo is not -- does not have an immortal soul that when you are destroying that embryo you in addition risk the full gravity of killing a human person in the full sense. But ensoulment is not the factor that means the difference between moral right or wrong or even the difference between something that would be seen as an abortion as versus contraception.