Twinning and ensoulment

A friend told me about the great Jimmy Akin's blog post on identical twinning and ensoulment. The Catholic doctrine is that for a normal, non-twin embryo, God creates the rational soul at the moment of conception. (Please note that this issue of ensoulment is only tangentially related to the issue of the humanity of the embryo from the moment of conception. Ensoulment is a matter of faith and possibly natural theology, while recognizing the humanity of the embryo requires no faith and is a matter of natural philosophy, i.e., science and not faith.)

Identical twins occur when the single fertilized egg (i.e., embryo) splits into two embryos. Akin lays out two possibilities in the blog post. Either the single soul (A) present at conception persists and another soul (B) is created in addition; or else the single soul (A) is destroyed and two new souls (B and C) are created to take her place. Neither of these scenarios are altogether satisfying. Is one soul subordinate to the other, or else are they equal and God has quickly killed the initial soul?

Let me lay out a third possibility: the single embryo splits into two embryos because there are two souls present. After, just because we don't see manifestations of two souls doesn't necessarily mean that two souls aren't present, especially as an embryo is such a slight entity.

One weakness of this position is that it doesn't seem to explain what happens when an embryo is split by an external agent, as for example, in a test tube by a technician. Regarding this situation, the first comment to the linked blog post (by Jim Scott 4th) says it well: "God knows the actual future with infallible certainty & thus logically can create two souls for a single zygot destined to become twins." In this situation, the duality of souls isn't a cause of twinning, but is just along for the ride, so to speak—an explanation no worse than Akin's non-causal descriptions. And heck, if you're going to invoke God for ensoulment, why not have him employ his powers?