In Evangelium Vitae, St. John Paul II pointed to modern scientific research to support the beginning of human life in the womb.
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When defending the Catholic Church’s pro-life views, St. John Paul II turned to science to explain why the Church is against abortion.
He detailed the science behind the Church’s view in his encyclical Evangelium Vitae.
Some people try to justify abortion by claiming that the result of conception, at least up to a certain number of days, cannot yet be considered a personal human life. But in fact, “from the time that the ovum is fertilized, a life is begun which is neither that of the father nor the mother; it is rather the life of a new human being with his own growth. It would never be made human if it were not human already. This has always been clear, and … modern genetic science offers clear confirmation. It has demonstrated that from the first instant there is established the program of what this living being will be: a person, this individual person with his characteristic aspects already well determined. Right from fertilization the adventure of a human life begins, and each of its capacities requires time-a rather lengthy time-to find its place and to be in a position to act.”
St. John Paul II is referring to the reality that when fertilization occurs, something happens and a new living organism is created. This organism is different from the father or mother and is entirely new, containing all the instructions that will provide for its growth and maturation.
While some philosophers and scientists may disagree about the precise moment of the beginning of human life, St. John Paul II points out that even the possibility that human life begins at conception should make us pause and consider what we are doing with abortion.
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
If science is not settled on the precise beginning of human life, St. John Paul II urges us to use caution anyway and not rush to kill another human being.