Marine creatures known as moon jellyfish possess eyes with sophisticated lenses that can create clear images revealing intricate details. However, the positioning of the moon jellyfish's retinas prevents them from capturing a sharp image, resulting in only a vague representation of objects that highlights major characteristics but lacks fine detail. This scenario illustrates that the structure of eyes is tailored to the specific requirements of an animal rather than adhering to an idealized concept of an effective eye design. The argument relies on which of the following assumptions?