The softer the face, the easier it is to move its features in small and subtle ways. Pliant facial features make it possible to perform a wider range of facial expressions that convey different emotions and ideas.
Modern-day humans look different from their prehistoric ancestors and relatives. They bear even less of a resemblance to bonobos and chimpanzees, their closest extant relatives.
Researchers from the University of York investigated the evolution of the human face. They started with ancient humans, progressed through later species and subspecies like the Neanderthals (Homo neanderthalensis), and finally reached modern humans.
Their study showed that social communication might have played a critical role in the way the facial features of humans evolved. In addition to social factors, the York researchers also identified biomechanical and physiological influences. (Related: Advanced communication? Spider monkeys adjust their “whinnies” to regain contact with their group.)
Human facial features grew softer to enable non-verbal communications
York researcher Paul O'Higgins and his teammates said that climate and diet were not the only factors in the evolution of facial features. Human faces also changed to make it easier to gesture and communicate through non-verbal means.
Early humans survived and flourished due in no small part to their propensity for forming communities. Gesturing and non-verbal communications are vital in large social networks.
“We can now use our faces to signal more than 20 different categories of emotion via the contraction or relaxation of muscles,” explained O'Higgins. “It's unlikely that our early human ancestors had the same facial dexterity as the overall shape of the face and the positions of the muscles were different.”
Ancient human species displayed a prominent brow ridge similar to those on gorillas and other great apes. Modern humans, on the other hand, have far smoother foreheads.
Modern humans also have visible eyebrows with lots of hair. Their flexible eyebrows have a broader range of movement.
Finally, the face of modern humans are slimmer in comparison to their ancestors. The combination of these various facial features make it easy for humans to show their emotions without making a sound, such as raising an eyebrow in surprise.
Communities and diets also influenced the evolution of the human face
“We know that other factors such as diet, respiratory physiology and climate have contributed to the shape of the modern human face, but to interpret its evolution solely in terms of these factors would be an oversimplification,” remarked O'Higgins in a statement.
His team noted that the mechanical requirements of eating affected the shape of the human face. Chewing tough food required strong facial muscles that took up lots of space, so early humans had broad faces.
As humans learned how to soften their meals by cooking and processing food, they didn't have to chew as hard and as often. Their facial muscles and faces grew smaller.
The York researchers said that the human face started shrinking faster after the appearance of agricultural communities. Humans exchanged the hunter-gatherer lifestyle for one focused on farming.
The growth of these communities into sprawling cities changed human lifestyles and diets even further. Today's heavily processed foods take little physical effort to consume.
O'Higgins said that there are hard limits on the ability of the human face to change itself. But within those limitations, facial features will keep adapting to the environment, cultures, and societies that humans encounter and live in.
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