One of the most awesome characteristics of planet Earth is that it has an atmosphere. Thanks to it, we are able to communicate with each other verbally (sound requires a medium to propagate, which in this case is air). We evolved to develop ears only because there was air in the atmosphere.
Well, what if there was no air? How would we communicate? Most people would ask how we would survive without air in the first place. I am talking of a hypothetical situation where we would be able to survive without it. Who knows? Maybe there’s a planet out there with no air. Imagine a thunderstorm with no sound. Such a waste!
The first thing that comes to mind is sign language. I wonder how much further we would have advanced from simple signing. For example, with, sound, we began by making simple noises, then advanced to simple words, then sentences and so on. Now we have cell phones, voice recorders and Daft Punk. What if we had advanced the same way with something like sign language? I am guessing facial expressions would play a much greater role. The conveyance of feelings would be a thing? (anyone who watched The Arrival can relate). I can imagine a world full of professor Xs walking around in silence yet communicating with each other just fine.
The environment directly influences the way we evolve (perfect time to bring up environmental awareness but who gives a shit). What if there exists a planet with a completely different type of environment inhabited by completely different beings? How cool/nightmarish would that be?