It is my understanding that the Church allows for the belief in the creation of the human body through theistic evolution but teaches that the soul is created immediately by God. In a recent debate, I ran into the following common argument:
Given evolution, there would have to be an instance in our ancestral past where God gives a human soul to some child, but not to his parents. This seems arbitrary and inelegant, since there would be little perceptible difference between the child and his parents, and hence no particular reason why the child should exist eternally while his parents do not. Thus, the inherent inelegance introduced makes accepting this doctrine ad hoc as opposed to the simpler solution of rejecting it.
One could suggest that the soul is a prerequisite for sentience and/or personhood, but that seems to open up another complicated can of worms. If nothing else, a debater would claim that evolution entails the gradual development of sentience.
I would just like to know if anyone has had thoughts about this or would like to share.