An interesting article trying to answer why only humans have chins. But, apparently no one could give the explanation. There are several theories hat divide the researchers. The most heavily promoted explanation is that chins are adaptations for chewing—that they help to reduce the physical stresses acting upon a masticating jaw. But the chin would make things worse. The lower jaw consists of two halves that are joined in the middle; when we chew, we compress the bone on the outer face of this join (near the lips) and pull on the bone on the inner face (near the tongue). Since bone is much stronger when compressed than pulled, you'd ideally want to reinforce the inner face of the join and not the outer one. In other words, you'd want the opposite of a chin. 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. Some blame the sex. Men typically have bigger chins than women, and stronger chins are often equated with attractiveness. Perhaps the chin is a sexual ornament, the human equivalent of a stag's antlers or a peacock's tail, a way of attracting mates or perhaps even signaling one's health and quality. One century-old idea considers chins as adaptations for deflecting punches to the face. That is, they helped early humans to take one on the chin. But in reality, chins are terrible for deflecting blows, often resulting in broken jaws. Maybe chins aren't adaptations at all. More likely they may be spandrels—incidental features that have no benefits in themselves, but are byproducts of evolution acting upon something else. http://www.theatlantic.com/science/...imals-with-chins-and-no-one-knows-why/431625/ What do you think?