Most people think visual information is more important than aural information - like, what's this big deal about sound? And why should I bother to listen, rather than look? And here are the facts: there are blind species, in the backs of the caves, the bottoms of the oceans. It's not essential on planet Earth to be able to see, to be a species. But there are no deaf animal species. You have to be able to hear, or you won't get the information you need in order to survive.