Well, here's what this article says about speech: Others have suggested that the chin is an adaptation for chinwags: It resists the forces we create when speak

Well, here's what this article says about speech: Others have suggested that the chin is an adaptation for chinwags: It resists the forces we create when speaking. After all, speech is certainly a feature that separates us from other living animals. But there's no good evidence that the tongue exerts substantial enough forces to warrant a thick chunk of reinforcing bone. That's not my first thought at all. I think it has absolutely to do with speech, but not for that reason. I think it's to create more space for the tongue to move around and make different sounds. Just another SWAG, of course, but I'm surprised not to see this idea floated.