Hi everybody! (I feel late and breathless, as usual.)
Here’s a bad analogy, but it might help: Say you had a computer programmed to run a self-replicating and cumulatively developing system. However, the computer only works if it’s plugged in. The computer would be DNA, the DNA code would be the program, the plugging into animating power would be the soul.
The reason this is such a bad analogy (it gets worse the more I think about it) is that, as the second post said, in CC theology the soul is non-material, but electricity is material.
DNA itself, in other words, is no more than another feature of a human body, in some respects like another organ. The anima or psuche or soul is the animating, life-giving principle directly infused by God at conception. DNA directs our development, but the soul gives life to the DNA components brought together at the oocyte and zygote levels.
Another way of putting it is that humans procreate, and God creates. The soul is created by God; it has nothing to do with DNA, in standard CC theology. DNA is part of the “matter” of the human body; the soul is the non-physical “form” of the body.
So which makes us human, our DNA or our soul? Surprisingly, it’s the soul. The DNA is “coded” for the development of Homo sapiens, but would not begin to develop into Homo sapiens without the divine infusion of the human soul at conception. There would be no human without a human soul.
Could something develop with human DNA into a human shape, but without a soul? No, according to the CC, because it’s the soul that makes the body live and begin to develop in the first place.
Aquinas, by the way, thought the initial development of the zygote was vegetable in nature, then animal, then finally human. But that’s just because he didn’t know about the DNA code (today he would correct his biological mistake, but retain the philosophy behind it). The philosophical principle still remains the same: if it’s living and developing, it has a soul.