Unique Human Chin 人類獨有的下巴

A couple of days ago read an article claming humans the only mammals that have chins but evolution can not explain why. Another article stated the reason due to shrinkage of human face but didn't explain why. I believe two reasons. Human mouth no longer a weapon and main survival tool of the human body, its functions changed, therefore structure and shape changed over time accordingly. Walking upright constantly resulted in the shrinkage of the human face and its center of gravity shifts backward for better upright walking and weight redistribution. There are, of couse, maybe other minor factors, such as cooked food or intentional selection of looks different from "animals".