[Mike Fieschko]

Aquinas did not have a microscope at his disposal.

Quite true. Yet the division between 'form' and 'matter' which he developed from Aristotle might have restricted his ability to identify the time when 'humanness' reaches existence. Did Aquinas ever discuss tadpoles? (Not meant in jest.)

[HowlinglyMind-BendingAbsurdity]

It would be impossible to discuss the "spark of life" gene discovery without some type of conceptual teleology vaguely reminiscent of Aristotelian and Thomistic philosophy.

[RobbyS]

I think that Aristotle, whose forte was biology, would not have adopted the doctrine of the quickening if he had had a microscope. If he could have seen a sperm penetrate the ovuum and witnessed the beginnings of the "motion" that indicates life he would have had a different opinion. His philosophy, after all, was based on his personal observations. Aquinas was simply following the master in his conclusions. As I recall, Duns Scotus believed in conception as the first moment of life because he supported the dogma of the Immaculate Conception. So brilliant were his arguments in favor of it that the Church accepted them and rejected the contrary views of Aquinas. So, theology finds the truth, some four hundred years before science verifies the process of epigenesis.