Unlike the nearest species to homo sapiens such as chimpanzees or erstwhile Neanderthals, only humans or homo homo-sapiens have chins and it was long believed that this was by virtue of our constant chewing or eating ability. But a new study shows that it was not due to mechanical forces but resulted from an evolutionary adaptation involving face size and shape.
The study says the link is possibly due to changes in hormone levels as humans became more social and their brains began to shrink in size. “Primates or the Neanderthals did not have chins. In some way, it seems trivial but a reason why chins are so interesting is we are the only ones who have them. It is unique to us,” said lead author Nathan Holton from the University of Iowa.
Studying advanced facial and cranial biomechanical analyses of about 40 people, the Iowa varsity team said mechanical forces like chewing is hardly capable of producing the resistance needed for new jaw bone that was absent in monkeys or chimpanzees, to be created in the lower mandible of only humans. Instead, they say, the chin’s emergence arose from simple geometry.
“As our faces became smaller in our evolution from archaic humans to today – in fact, our faces are roughly 15 percent shorter than the Neanderthals – the chin became a bony prominence, the adapted, pointy emblem at the bottom of our face,” Holton, who conducts research on biomechanics, said.
Human chin is the second-most important development owing to lifestyle change, starting about 80,000 years ago. If this theory is to be believed, new Internet age that makes humans less interactive physically or socially but more aggressive online with gadgets may lead to our progeny develop protruding eyes, say in 10,000 years from now.
Ever since humans tranformed from hunter-gatherer groups to modern social cooperative groups , males began to learn the need to live in tranquility or peace, instead of fighting over territory and other belongings, which resulted in less harmonal levels of testosterone, reducing the male craniofacial region, explain researchers.
When face became smaller, the retrenching effect or a physiological departure created a natural opportunity for the human chin to emerge. Even to this day, children have flat, imperceptible chins like in the Neanderthals but they grow their bony chin as they enter adulthood, say researchers.
“Our study suggests that chin prominence is unrelated to function and probably has more to do with spatial dynamics during development,” the authors said in their paper published in the Journal of Anatomy.
In a similar research done earlier, anthropologists Matthew Skinner and Tracy Kivell from University of Kent examined the internal spongy structure of bone called trabeculae of hand bones that differentiates humans from chimpanzees with a unique gripping ability between thumb and fingers.
The grip led humans to stand in posture unlike chimpanzees, who cannot adopt human-like postures. In fact, this unique human pattern helped make tools and led them to evolve faster than other species to develop brain’s cognizable features.
The results “provide skeletal evidence that our early ancestors used human-like hand postures much earlier and more frequently than previously considered,” the authors from University of London noted.