Researchers have discovered that the ear bones of mammals are homologous structures with parts of fish jaws. this suggests that fish do not require a sense of sound. fish and mammals have a distant common ancestor. selection pressures have promoted similar evolution in fish and mammals. selection pressures have acted over time on mammals but not fish.

The answer here is FISH AND MAMMALS HAVE A DISTANT COMMON ANCESTOR. Homology is the similarity in structure, physiology or development of different species of organisms based upon their descent from a common evolutionary ancestor, having common evolutionary ancestry. The ear ossicles of tetrapods (including extinct and living amphibians, reptiles and mammals) are homologous to bones in a fish jaw. The stapes, incus, and malleus of the mammalian ear are homologous of parts of the fish jaw and gill arches. As early fish evolved jaws, the gill arches closest to the mouth acted as jaw bones. The mandibular arch, became the upper and lower jaws. The hyoid arch extended from the quadrate bone to the angle of the jaw supports the jaw and later became the hyomandibular bone, which braces the quadrate bone in bony fish. As tetrapods evolve from one group of lobe-finned fish, quadrate bone fused with the skull giving it a stronger bite. This meant that the hyomandibular bone no longer function as the jaw support but since it is close to the ear, it seems that it transfers vibrations to the inner ear. To date, it is one of the most appealing stories of evolution: transition of ancestral fish jaw bones into the tiny middle ear bones which happens as it came out in the water and starting to hear in air. 

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