Well, auditory organs -- ranging from ears to skin that can sense the vibrations that make up sound -- have an evolutionary survival advantage even if other creature aren't intentionally trying to communicate with you; being able to sense sound means being able to sense approaching danger, for example.

There's been a lot of work done into scanning the wildly-incomplete fossil record for waystations on the emergence of the modern ear, including some recent findings: https://www.scientificamerican.com/article/now-hear-this-new-fossils-reveal-early-ear-bone-evolution/