The problem of the origin of life has given rise in the last centuries to a debate between the Mechanicists and the Vitalists.
Although the problem was not confronted directly and explicitly by St. Thomas, he would have chosen the alternative of creation
by God, instead of merely chance, says Mondin.24 Therefore, St. Thomas would incline to say that God is involved
in the origin of life.
Although St. Thomas affirms the absolute primacy of God as the principle cause of everything produced by nature, does St.
Thomas affirm that God works through secondary causes too? In his argument against St. Augustine and Avicenna,25
St. Thomas asserts that not just God and spirits are efficient causes, but there are secondary causes in nature. St. Thomas
affirms there are secondary causes in nature.26 As proof of secondary causes, St. Thomas has three arguments (Aquinas
Summa Theologiae 1. 105. 5).27 First, without secondary causes there would be no connection for creatures
between their causation and the effect; creatures would be impotent and their powers in vain. Second, every being exists through
its operations, so that without secondary causality, creatures existence would be imperiled. Third, less perfect things are
ordered to more perfect: matter is ordered to form as the first act, and matter is ordered to operation as the second act,
in such a way that operation is the goal of created things. Therefore, St. Thomas confers upon secondary causes the full share
of being and efficacy to which they are due. In the real world, the nature of the effect is similar to the nature of the cause,
so that warmth does not chill, and humans generate humans. So the existence of natural laws suppose that God created beings
endowed with causality.28 How can the same effect be produced by two different causes (God and the natural agent)
at the same time? These causes are at the same time, but not under the same relation, e.g., a workman uses an axe to cut wood,
and both are causes. The analogy applies to God, but God’s influence on the secondary cause penetrates more deeply,
so that when God grants existence, God grants form, movement, and efficacy.29 Thus the existence of secondary causes
points to no lack of power in God, but to the immensity of God’s goodness (confer: Aquinas Summa Contra Gentiles
1. 13).30 Philosophically, secondary causality in creatures is an affirmation of the principle of causality
which is fundamental to classical metaphysics and especially to Thomistic metaphysics. The principle of causality regulates
the relationship between cause and effect according to the definition of Aristotle, which St. Thomas made his own, declaring,
"Everything that is moved is moved by another," or in another way, "Everything that happens presupposes a principle that produces