According to scientists, humans are the only animals, aside from elephants for some reason, to sport a bony protrusion at the end of the lower mandible. No other ape – not chimps nor gorillas nor orangutans – has one. Not even the Neanderthal, our nearest evolutionary relative, had a chin.

It was reported in the April 16 Science Notebook of the Christian Science Monitor, that some scientists have argued that the bony material on the chin grows as one develops into adulthood as a result of mechanical forces, buttressing the back of the jaw to help with chewing. But a new analysis tells a different story.

Led by Nathan Holton, an anthropologist in the Department of Orthodontics at the University of Iowa’s College of Dentistry, the research team analyzed data from the Iowa Facial Growth Study, which took periodic craniofacial measurements of male and female subjects ranging from toddlers – who generally don’t really have much of a chin to speak of – to twentysomethings, who usually do (even if it seems as though half of them are covered with beards). They found that the mechanical forces generated by chewing are not capable of producing the resistance that would create new bone at the tip of the jaw.

“In short, we do not find any evidence that chins are tied to mechanical function and in some cases we find that chins are worse at resisting mechanical forces as we grow,” said Holton in a UI news release. “Overall, this suggests that chins are unlikely related to the need to dissipate stresses and strains and that other explanations are more likely to be correct.”

The Christian Science Monitor reported that researchers’ findings show that beginning about 80,000 years ago, and accelerating about 20,000 years later following another wave of human migration out of Africa, human faces changed. The human brow ridges became less prominent, and most parts of human faces shrank, except for the chin, which then appeared more prominent.

And it all happened, researchers argue, because humans started developing wider social networks. This high level of social interaction, anthropologist Kim R. Hill and his colleagues propose, is what allows humans, unlike chimps, to accumulate improvements over time.