Benedict XVI:

"... With regard to the embryo in the womb, science itself highlights its autonomy capable of interaction with the mother, the coordination of biological processes, the continuity of development, the growing complexity of the organism. This is not an accumulation of biological material, but a new living being, dynamic and wonderfully ordered, a new unique human being. So was Jesus in Mary's womb, so it was for all of us in our mother’s womb…there is no reason not to consider him a person from conception."

(via Rorate Caeli)

The Feast of the Annunciation -- the Church's proof that the soul is infused at conception? Except this is not what the Holy Father seems to be saying here, just that contemporary embryology maintains that human life begins at conception. Nothing about the infusion of the rational soul.