It was intended to address the issues arising from both the "higher criticism" and new scientific theories, and their relation with Scripture. Nothing specific concerning evolution was said, and initially both those in favour and against evolution found things to encourage them in the text; however a more conservative interpretation came to be dominant, and the influence of the conservative Jesuit Cardinal Camillo Mazzella (with whom Leo had argued over Mons. D'Hulst) detected. Leo stressed the unstable and changing nature of scientific theory, and criticised the "thirst for novelty and the unrestrained freedom of thought" of the age, but accepted that the apparent literal sense of the Bible might not always be correct. In biblical interpretation, Catholic scholars should not "depart from the literal and obvious sense, except only where reason makes it untenable or necessity requires". Leo stressed that both theologians and scientists should confine themselves to their own disciplines as much as possible. An earlier encyclical of Leo's on marriage, Arcanum Divinae Sapientiae (1880), had described in passing the Genesis account of the creation of Eve from Adam's side as "what is to all known, and cannot be doubted by any." The Pontifical Biblical Commission issued a decree ratified by Pope Pius X on June 30, 1909, that stated that the literal historical meaning of the first chapters of Genesis could not be doubted in regard to "the creation of all things by God at the beginning of time; the special creation of man; the formation of the first woman from the first man; the unity of the human race". As in 1860, "special creation" was only referred to in respect of the human species. Pope Pius XII Pope Pius XII's encyclical of 1950, Humani generis, was the first encyclical to specifically refer to evolution and took up a neutral position, again concentrating on human evolution: Pope Pius XII's teaching can be summarized as follows: The question of the origin of man's body from pre-existing and living matter is a legitimate matter of inquiry for natural science. Catholics are free to form their own opinions, but they should do so cautiously; they should not confuse fact with conjecture, and they should respect the Church's right to define matters touching on Revelation. Catholics must believe, however, that humans have souls created immediately by God. Since the soul is a spiritual substance it is not brought into being through transformation