Found a link to this article on humans being the only animal with a chin. It goes into an evolutionary argument on why it developed. It seems obvious why, because how could we think on the throne without it. In my awareness exercise about differentiating the head and jaw I found that that I use the sublingual musculature differently on the left and right side of the midline. It feels to me the my left side musculature normal posture is more contracted to give the right more freedom and control. In fact in terms of felt initiated movement the left side did not exist but instead reacts subordinately to the right side initiated movement.
To generate melodious sound on the left it feels that I need to be able to allow the left side to vibrate or relax and contract rapidly. In playing with this area I have difficulty in getting the musculature to relax and lengthen. It affects the position of the mandible on the left as compared to the right. It is still developing but in lengthening of the left sublingual musculature the left mandible seems to extend more forward. The angle of the jaw on the left also relaxes and come forwards in response. This then seems to influence the left lateral and then the left posterior musculature of the neck. So in order to use the left sublingual musculature in a differentiated way I find there is a global change of use of the head.