The existence of evil in a world created by God raises very difficult questions to answer. Under the inspiration of Thomistic philosophy, in this article we face this problem first of all “from below”, trying to understand the meaning of physical evils in living nature, especially in animals (pain, aggressive interactions). Secondly, in thinking of the enormous amount of moral evil in the human world, we consider the biblical faith in original sin as illuminating. We examine some points of Thomas Aquinas in this regard, especially his thesis that the physical cosmos is not affected by original sin and that the loss of man’s primitive happy situation involves a contradiction between his spiritual aspirations and his mortal nature subject to limits and suffering. This situation is remedied by the help God gives man through his ordinary Providence, which includes a personal struggle against evil, and above all through his salvific plan which we know thanks to the biblical faith.