I got this by e-mail, and it is worthy of wider reading:
De Abortu (1974), in footnote 19, says:
"This declaration expressly leaves aside the question of the moment when the spiritual soul is infused. There is not a unanimous tradition on this point and authors are as yet in disagreement. For some it dates from the first instant; for others it could not at least precede nidation. It is not within the competence of science to decide between these views, because the existence of an immortal soul is not a question in its field. It is a philosophical problem from which our moral affirmation remains independent for two reasons: (1) supposing a belated animation, there is still nothing less than a human life, preparing for and calling for a soul in which the nature received from parents is completed, (2) on the other hand, it suffices that this presence of the soul be probable (and one can never prove the contrary) in order that the taking of life involve accepting the risk of killing a man, not only waiting for, but already in possession of his soul."
In other words, in 1974 the CDF was explicitly not willing to say that the soul is infused at conception, while stating unequivocally that abortion is already wrong no matter what.
Evangelium Vitae 60 comes closer, but still doesn’t quite get to the point of saying for sure.
In light of that, I’m not sure exactly what the House Republicans were looking at, nor what weight it has, but it seems to me that the CDF and JP II would surely be aware if the question had been resolved 300 years ago. (Some also try to cite Ineffabilis Deus in support of this, but the same objection holds in my mind.)
None of that gets Ms. Pelosi off the hook, because both De Abortu and Evangelium Vitae (and the whole tradition of the Church) are quite clear that the question of ensoulment and whatever that might mean for the precise nature of the life taken in an early term abortion is a question that doesn’t make an ounce of difference either way in determining that abortion is always and everywhere wrong.