According to a recent statement by Catholic bishops, "The Church recognizes that the obligation to protect unborn human life rests on the answer to two questions, neither of which is private or specifically religious.The first is a biological question: When does a new human life begin? When is there a new living organism of the human species, distinct from mother and father and ready to develop and mature if given a nurturing environment? While ancient thinkers had little verifiable knowledge to help them answer this question, today embryology textbooks confirm that a new human life begins at conception... The Catholic Church does not teach this as a matter of faith; it acknowledges it as a matter of objective fact."
Now that is the most preposterous abuse of science that any of us are likely to see in a lifetime. Scientific knowledge is contextual. In the context of biochemistry, the embryo is indeed a separate organism: its DNA, and the peptides and proteins derived from that DNA, are distinct. But the physiology the fetus is, until birth, completely dependent for the requisites of life on the pregnant woman's organism. Physiologically the fetus is, until the moment of birth, part of the pregnant woman's body - part of a single functioning physiological system. Why does the Church take the perspective of biochemistry to be more "scientific," claiming that it ought to be imposed by the state, even on unbelievers, by force, as a matter of "natural law," and ignore the equally scientific - and much more directly relevant - perspective of physiology? Because the biochemistry fits the Church's prior doctrine, and physiology doesn't. Like the proverbial drunk with a lamp-post, the Church picks one bit of science, and ignores the rest, because it is using science for support - preferring this dishonest claim of support to objective illumination. This swindle - for that is what it is - is dishonest enough to disqualify the Church, even if one were to ignore its other crimes, from any claim to genuine moral authority. Either on abortion or on anything else.