Some people feel that because the Church has no definitive statement on when ensoulment takes place, it is okay to allow abortion and to use early embryos for research. What does the Church say about this?
The Declaration on Procured Abortion states the following:
In the course of history, the Fathers of the Church, her pastors, and her Doctors have taught the same doctrine—the various opinions on the infusion of the spiritual soul did not introduce any doubt about the illicitness of abortion. It is true that in the Middle Ages, when the opinion was generally held that the spiritual soul was not present until after the first few weeks, a distinction was made in the evaluation of the sin and the gravity of penal sanctions. Excellent authors allowed for this first period more lenient case solutions which they rejected for following periods. But it was never denied at that time that procured abortion, even during the first days, was objectively grave fault. This condemnation was in fact unanimous . . . Most recently, the Second Vatican Council, presided over by Paul VI, has most severely condemned abortion: "Life must be safeguarded with extreme care from conception; abortion and infanticide are abominable crimes." The same Paul VI, speaking on this subject on many occasions, has not been afraid to declare that this teaching of the Church "has not changed and is unchangeable." (7)
Concerning the issue of ensoulment and embryonic stem cell research, Evangelium Vitae teaches that
Even if the presence of a spiritual soul cannot be ascertained by empirical data, the results themselves of scientific research on the human embryo provide a valuable indication for discerning by the use of reason a personal presence at the moment of the first appearance of a human life: How could a human individual not be a human person? (EV 60)
Furthermore, what is at stake is so important that, from the standpoint of moral obligation, the mere probability that a human person is involved would suffice to justify an absolutely clear prohibition of any intervention aimed at killing a human embryo. Precisely for this reason, over and above all scientific debates and those philosophical affirmations to which the Magisterium has not expressly committed itself, the Church has always taught and continues to teach that the result of human procreation, from the first moment of its existence, must be guaranteed that unconditional respect which is morally due to the human being in his or her totality and unity as body and spirit:
The human being is to be respected and treated as a person from the moment of conception; and therefore from that same moment his rights as a person must be recognized, among which in the first place is the inviolable right of every innocent human being to life. (EV 60)