“They are presented as alternatives that exclude each other,” the pope said. “This clash is an absurdity because on one hand there is much scientific proof in favor of evolution, which appears as a reality that we must see and which enriches our understanding of life and being as such.” Pope Benedict had no problem with the scientific theory of evolution. According to the poster I was responding to, that must mean he was confused about his Christian faith.
HUMANI GENERIS has never been an endorsement of universal common descent, but a warning of these dangers:
1. Christian culture being attacked on all sides
2. men easily persuade themselves in such matters that what they do not wish to believe is false or at least doubtful
5.Some imprudently and indiscreetly hold that evolution, which has not been fully proved even in the domain of natural sciences, explains the origin of all things,
6. Such fictitious tenets of evolution which repudiate all that is absolute, firm and immutable, have paved the way for the new erroneous philosophy
7. There is also a certain historicism, which attributing value only to the events of man's life, overthrows the foundation of all truth and absolute law, both on the level of philosophical speculations and especially to Christian dogmas.
10. desirous of novelty, and fearing to be considered ignorant of recent scientific findings, try to withdraw themselves from the sacred Teaching Authority and are accordingly in danger of gradually departing from revealed truth and of drawing others along with them into error.
11. some questioned whether the traditional apologetics of the Church did not constitute an obstacle rather than a help to the winning of souls for Christ
12 the removal of which would bring about the union of all, but only to their destruction.
17. things (truths of the faith) may be replaced by conjectural notions and by some formless and unstable tenets of a new philosophy, tenets which, like the flowers of the field, are in existence today and die tomorrow;
22. For some go so far as to pervert the sense of the Vatican Council's definition that God is the author of Holy Scripture, and they put forward again the opinion, already often condemned, which asserts that immunity from error extends only to those parts of the Bible that treat of God or of moral and religious matters.
28. These and like errors, it is clear, have crept in among certain of Our sons who are deceived by imprudent zeal for souls or by false science. To them We are compelled with grief to repeat once again truths already well known, and to point out with solicitude clear errors and dangers of error.
In other words, Humani Generis is warning against the dangers of wholesale universal common descent. What the encyclical really says is that Catholics are at liberty to speculate about evolutionary scenarios. This is in no way shape or form a ringing endorsement of evolution as natural history. What was outright condemned as heresy is the belief that Adam and Eve represented a certain number of first parents. This is called polygenism.
37. When, however, there is question of another conjectural opinion, namely polygenism, the children of the Church by no means enjoy such liberty. For the faithful cannot embrace that opinion which maintains that either after Adam there existed on this earth true men who did not take their origin through natural generation from him as from the first parent of all, or that Adam represents a certain number of first parents. Now it is in no way apparent how such an opinion can be reconciled with that which the sources of revealed truth and the documents of the Teaching Authority of the Church propose with regard to original sin, which proceeds from a sin actually committed by an individual Adam and which, through generation, is passed on to all and is in everyone as his own. (Humani Generis 37)
There is a reason that Rome must affirm the historicity of Adam and original sin and it's not because of Moses, it's because of Paul. Original sin is a Pauline doctrine and Paul explicitly states that the reason that all sin is because when Adam ate of the forbidden fruit, we did not fast.
I have never seen any Christian argue that creation is not an essential doctrine.
Because they can't, the real question is what it includes.