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?
Interesting in this regard: Soon after the human skeleton allowed to close a good fist for punching, the facial skull began to develop stronger. It seems our ancestors were big fans of fist fights, and it was an advantage to be able to take punches to the face without getting harmed too much. Fits perfectly to the idea that a stronger chin was needed. With a broken jaw, one cannot eat properly, and this was likely a killer injury in those times. I put my bet on a mix: Females saw that males with stronger chins were more effective combat, "better protectors" and developed an inbuilt favorite for the chins (Women chosing mens with stronge chins had a slightly increased change that their offspring was protected well enough to make it to adulthood, and so over time, nature selected for this bias). Independently, the male parts of the genome evolved to give a stronger facial skull and chin, just for the increased direct survival - in addition to the higehr chance for mating, due to the selection in women. So there were probably two selections working in favor of the chin. My nephew had a badly broken jaw after a bicycle accident. This is a crippling thing. He was in hospital an got fed with nourishment fluids via some sort of pipe through his nose down to his stomach. In ancient times, he might have starved. A stronge chin could save lives, I'm pretty sure. And nature always selects for life-savers.
