" The view of the Catholic Church on biological evolution has been cautious. In Humani Generis, Pius XII permitted discussion of evolution by competent thinkers, but warned against any presumption that evolution has been proved true, "as if there were nothing in the sources of Divine Revelation which demands the greatest moderation and caution in this question". Pius XII's caution was justified; since his death the theory has had some resounding problems. "

― , The Unicorn in the Sanctuary: The Impact of the New Age Movement on the Catholic Church