Because most Christians would agree with what is called “micro evolution” or “environmental evolution” which is the creature adapting to its surroundings overtime. We can point to all sorts of examples of this -Antibiotic resistant bacteria -pesticide resistant insects -Darwin’s finches -Lactose tolerance in humans Denying evolution would be saying that science and faith are contradictory when they are in fact complimentary. The church holds that these things happen under the guidance of God. The church still holds to the story of creation in Genesis but realizes that overtime our bodies adapt to our surroundings and this is because of Gods divine guidance. We can even see this recently. We see humans in high carb diet areas who have more amylase gene, Tibetans who have adapted to higher climates to breathe better, the Bajau people have spleens that are 50% larger than average that are able to hold more red blood cells which helps them with deep diving, and also in Africa we see the sickle cell trait as a response by the body to malaria. For instance if Protestants hold that dinosaurs never existed (many do) yet science was to find a perfectly preserved body of a T-Rex then that would mean science has refuted God for the Protestant but for the Catholic it would be seen as an affirmation of Gods creation and divine order. Thus one must hold that science and faith are complimentary and not contradictory.