A recent post by Eric MacDonald touches on the Catholic doctrine that human beings have very special souls, souls that represent an ontological leap vis-a-vis all other life on earth. (Of course, this belief is shared by many others, but it is the Catholic version we discuss here.)
One sees the naive attractiveness of this view. As we look around us, there certainly seems (as there seemed to Aristotle) to be an ontological gap between humans and other animals. For creationists, this gap is just a fact giving rise to no paradoxes. But Catholicism tries to pass itself off as a religion for thinking people, and so claims to have come to terms with evolution.
The obvious problem with this doctrine concerning souls is that it implies a binary choice – human soul or animal soul – and as a consequence, considering all hominids over time, there must exist a subset – call them the Progenitors – who were human but whose parents were not. (In fact Catholics are required specifically to believe that the Progenitors numbered exactly two – Adam and Eve.)
But can any sane person believe in the Progenitors? Consider language, one of the hallmarks of rationality. Did the Progenitors invent language for themselves? This is just not how it works. Language is acquired by human beings in infancy from their elders, not invented from scratch.
The ontological gap is (in some sense) a genuine feature of the world as we find it, but to assert that it necessitates an ontological leap that occurred at some definite time in the past is to assert something for which there is no evidence and that on the face of it is highly implausible.
So the Catholic claim to accept evolution is a misrepresentation. In fact they reject evolution at the point that has always been the most contentious: common descent as between humans and the rest of the animal world.