This then, was the point at which ancient science fixed the beginning of the individual human life. In making this determination, Aristotle was not saying anything about abortion, early or late. After all, he did not recognize the sacredness of human life.
For the longest time, Aristotle’s theory concerning the beginning of human life—known eventually as “mediate animation”—was the controlling view. It influenced St. Augustine and St. Thomas. It was the best science available—and Christian thinkers were very interested in using such science in the service of moral reasoning. As a consequence, the majority opinion was that abortion constituted actual homicide only after forty days. Earlier abortion, though still a sin, was classified either as contraception or as “anticipated homicide.”
Doing the best we can with the current best information is kinda a Catholic thing from the start. ‘Cus it’s human.